THE USE OF PROTON THERAPY AND CYCLOTRON PARTICLES ACCELERATION IN THE FIGHT AGAINST CANCER
THE USE OF PROTON THERAPY AND CYCLOTRON PARTICLES ACCELERATION IN THE FIGHT AGAINST CANCER
ABSTRACT
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. In 2015, about 90.5 million people had cancer. About 14.1 million new cases occur a year (not including skin cancer other than melanoma). It caused about 8.8 million deaths (15.7% of deaths). The general aim and objective of the study were to investigate the use of proton therapy and cyclotron particle acceleration in the fight against cancer. The study was made to be of help to national and international medical centers, cancer theatres, and private and government anti-cancer organizations, on the use of proton therapy and cyclotron particles acceleration in preventing and of curing cancer. Proton beam therapy is the latest advancement in the treatment of various types of cancer. It is a precise form of radiotherapy. It uses a beam of protons to target the cancer cells and destroys them. It scores high on precision and effectiveness when compared to other conventional cancer treatments like surgery, chemotherapy and X-ray radiotherapy. Proton beam therapy destroys the cancerous cells without harming the healthy cells. Thus it considerably reduces the side-effects that accompany conventional cancer treatments. Supporters say the technology allows physicians to treat a broad spectrum of cancers with few adverse effects, while more precisely targeting tumor cells with higher doses of radiation. Detractors say proton beam therapy is hugely expensive and is not superior to conventional radiation treatment. With proton beam therapy, physicians use a cyclotron to accelerate protons and fire them directly into tumor cells with submillimeter precision. Because healthy tissue is largely spared, oncologists can, in theory, deliver much higher doses of radiation, while improving local control and reducing the risk for recurrence and morbidities. Radiation therapy is one of the most frequently used methods for treating cancer patients. Therefore improving the quality of the treatment by using new irradiation technologies is one of the radiotherapist's constant concerns. The use of accelerators for delivering protons, heavier charged particles and secondary beams such as neutrons brings further improvement in dose distribution and in interesting biological properties for radiations producing a high Linear Energy Transfer (LET). Cyclotrons have been present in this field since the early history of radiotherapy and they could play a major role in future dedicated hospital-based facilities which include not only an accelerator but also specific beam-transport and beam-delivery systems. Modern cyclotron technology exists today to meet all of the requirements within a reasonable budget. Specific performances and several cyclotron designs are presented. For promotion and support the spreading of the medically dedicated particle accelerator facility and technology, the AG recommends that: The Agency should consider organizing seminars, regular meetings and CRPs on topics relevant to technological developments of proton therapy. The Agency should promote and support to make a standard QA program. Even if they used a different type of facility and technique, it would be necessary to assure the basic specification of the treatment beam and peripheral devices. The Agency should strengthen the mechanism for partial support for personnel from developing countries to attend the related meeting, such as PTCOG. The Agency should strengthen its collaboration with PTCOG meetings.
Also Read: Social Media a Double-Edged Sword for Students With Disabilities, Study Finds
TABLE OF CONTENTS
CHAPTER ONE: INTRODUCTION
1.1 Background of the Study
1.2 Problem of the Study
1.3 Aims and Objectives of the Study
1.4 Scope and Limitation
1.5 Significance of the Study
1.6 Definition of Terms
CHAPTER TWO
2.1 Introduction
2.2 Proton Interaction Mechanisms
2.3 Therapeutic Absorbed Dose Determination
2.4 Stray Radiation
2.5 Shielding Design
CHAPTER THREE
3.1 Proton Therapy
3.1.2. Description
3.2 Cyclotron Particle Acceleration
3.4. Treatment and Uses
3.5. Challenges and the Future of Proton Therapy
CHAPTER FOUR: SUMMARY, CONCLUSION, AND RECOMMENDATION
4.1 Summary
4.2 Conclusions
4.3 Recommendation
REFERENCES
https://www.uniuyo.edu.ng
ARE YOU SEEKING IN ADMISSION INTO UNIUYO?
UNIUYO UTME/DE FORM 2019/2020 IS OUT NOW
REGISTER FOR THE SCREENING
@ SIR PEE INTEGRATED SERVICES #3 College Road, Afaha Nsit – Phone: 07068634102
1.1 Background of the Study
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread to other parts of the body. Possible signs and symptoms include a lump, abnormal bleeding, prolonged cough, unexplained weight loss, and a change in bowel movements. While these symptoms may indicate cancer, they may have other causes. Over 100 types of cancers affect humans. Tobacco use is the cause of about 22% of cancer deaths. Another 10% are due to obesity, poor diet, lack of physical activity, and excessive drinking of alcohol. Other factors include certain infections, exposure to ionizing radiation and environmental pollutants. In the developing world, nearly 20% of cancers are due to infections such as hepatitis B, hepatitis C, and human papillomavirus infection. These factors act, at least partly, by changing the genes of a cell.
Legend: → tumor ←, ✱ central pleural effusion, 1 & 3 lungs, 2 spine, 4 ribs, 5 aorta, 6 spleen, 7 & 8 kidneys, 9 liver.
Specialty Oncology
Symptoms: Lump, abnormal bleeding, prolonged cough, unexplained weight loss, change in bowel movements
Risk Factors: Tobacco, obesity, poor diet, lack of physical activity, excessive alcohol, certain infections
Treatment: Radiation therapy, surgery, chemotherapy, and targeted therapy.
Prognosis: Average of five-year survival of 66% (USA)
Frequency: 90.5 million (2015)
Deaths: 8.8 million (2015)
Typically many genetic changes are required before cancer develops. Approximately 5–10% of cancers are due to inherited genetic defects from a person's parents. Cancer can be detected by certain signs and symptoms or screening tests. It is then typically further investigated by medical imaging and confirmed by biopsy.
Many cancers can be prevented by not smoking, maintaining a healthy weight, not drinking too much alcohol, eating plenty of vegetables, fruits, and whole grains, vaccination against certain infectious diseases, not eating too much processed and red meat, and avoiding too much sunlight exposure. Early detection through screening is useful for cervical and colorectal cancer. The benefits of screening in breast cancer are controversial. Cancer is often treated with some combination of radiation therapy, surgery, chemotherapy, and targeted therapy.
Pain and symptom management are an important part of care. Palliative care is particularly important in people with advanced disease. The chance of survival depends on the type of cancer and extent of disease at the start of treatment. In children under 15 at diagnosis, the five-year survival rate in the developed world is on average 80%.or cancer in the United States the average five-year survival rate is 66%.
1.2 Problem of the Study
In 2015, about 90.5 million people had cancer. About 14.1 million new cases occur a year (not including skin cancer other than melanoma). It caused about 8.8 million deaths (15.7% of deaths). The most common types of cancer in males are lung cancer, prostate cancer, colorectal cancer, and stomach cancer. In females, the most common types are breast cancer, colorectal cancer, lung cancer, and cervical cancer. If skin cancer other than melanoma were included in total new cancers each year, it would account for around 40% of cases. In children, acute lymphoblastic leukemia and brain tumors are most common except in Africa where non-Hodgkin lymphoma occurs more often. In 2012, about 165,000 children under 15 years of age were diagnosed with cancer.
The risk of cancer increases significantly with age and many cancers occur more commonly in developed countries. Rates are increasing as more people live to old age and as lifestyle changes occur in the developing world.
However there is a need for the doctors, nurses, and scientists as a whole to look into how proton therapy and the cyclotron particles acceleration can be and is used to fight off the increasing rate of cancer.
1.3 Aims and Objectives of the Study
The general aim and objective of the study are to investigate The Use Of Proton Therapy And Cyclotron Particles Acceleration In The Fight Against Cancer.
1.4 Scope and Limitation
The study covers the following areas:
i. The use of proton therapy and cyclotron particles acceleration in curing cancer.
ii. Challenges and the future of proton therapy
1.5 Significance of the Study
The study is made to be of help to national and international medical centers, cancer theatres, and private and government anti-cancer organizations, on the use of proton therapy and cyclotron particles acceleration in preventing and of curing cancer.
1.6 Definition of Terms
For clarification and certainty the following terms are defined to help the study:
1.6.1 Cancer
Cancers are a large family of diseases that involve abnormal cell growth with the potential to invade or spread to other parts of the body. They form a subset of neoplasms. A neoplasm or tumor is a group of cells that have undergone unregulated growth and will often form a mass or lump but may be distributed diffusely.
1.6.1. Proton Therapy
Proton therapy is a type of radiation treatment that uses protons to treat cancer. It’s also called proton beam therapy. A proton is a positively charged particle. At high energy, protons can destroy cancer cells. Doctors may use proton therapy alone. Or, they may combine it with other treatments, such as standard radiation therapy, surgery, chemotherapy, and/or immunotherapy. Proton therapy is a type of external-beam radiation therapy. It painlessly delivers radiation through the skin from a machine outside the body.
1.6.3. Cyclotron
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1934 in which charged particles accelerate outwards from the center along a spiral path.
1.6.4. Particle Accelerator
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to nearly light speed and to contain them in well-defined beams.
1.6.5. Therapy
Therapy is the treatment of someone with mental or physical illness without the use of drugs or operations.
1.6.6. Proton
A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons".
1.6.8 Interaction
Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect.
CHAPTER TWO
2.1 INTRODUCTION
This chapter is a concern with the proton interaction mechanisms, therapeutic absorbed dose determination, stray radiation, and shielding design.
2.2 PROTON INTERACTION MECHANISMS
A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons".
One or more protons are present in the nucleus of every atom; they are a necessary part of the nucleus. The number of protons in the nucleus is the defining property of an element and is referred to as the atomic number (represented by the symbol Z). Since each element has a unique number of protons, each element has its own unique atomic number.
The word proton is Greek for "first", and this name was given to the hydrogen nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen by atomic collisions. Protons were, therefore, a candidate to be a fundamental particle, and hence a building block of nitrogen and all other heavier atomic nuclei.
In the modern Standard Model of particle physics, protons are hadrons, and like neutrons, the other nucleon (particles present in atomic nuclei), are composed of three quarks. Although protons were originally considered fundamental or elementary particles, they are now known to be composed of three valence quarks: two up quarks of charge +2/3 e and one down quark of charge –1/3 e. The rest masses of quarks contribute only about 1% of a proton's mass, however. The remainder of a proton's mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. Because protons are not fundamental particles, they possess a physical size, though not a definite one; the root means square charge radius of a proton is about 0.84–0.87 FM or 0.84×10−15 to 0.87×10−15 m.
At sufficiently low temperatures, free protons will bind to electrons. However, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei until it is captured by the electron cloud of an atom. The result is a protonated atom, which is a chemical compound of hydrogen. In a vacuum, when free electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom, which is chemically a free radical. Such "free hydrogen atoms" tend to react chemically with many other types of atoms at sufficiently low energies. When free hydrogen atoms react with each other, they form neutral hydrogen molecules (H2), which are the most common molecular component of molecular clouds in interstellar space.
2.2.1. Interaction of free Protons with Ordinary Matter
Although protons have an affinity for oppositely charged electrons, this is a relatively low-energy interaction and so free protons must lose sufficient velocity (and kinetic energy) to become closely associated and bound to electrons. High energy protons, in traversing ordinary matter, lose energy by collisions with atomic nuclei, and by ionization of atoms (removing electrons) until they are slowed sufficiently to be captured by the electron cloud in a normal atom.
However, in such an association with an electron, the character of the bound proton is not changed, and it remains a proton. The attraction of low-energy free protons to any electrons present in the normal matter (such as the electrons in normal atoms) causes free protons to stop and to form a new chemical bond with an atom. Such a bond happens at any sufficiently "cold" temperature (i.e., comparable to temperatures at the surface of the Sun) and with any type of atom. Thus, in interaction with any type of normal (non-plasma) matter, low-velocity free protons are attracted to electrons in an atom or molecule with which they come in contact, causing the proton and molecule to combine. Such molecules are then said to be "protonated", and chemically they often, as a result, become so-called Bronsted acids.
2.2.3. Simple Explanation of Deuteron Structure and Binding (Proton-Neutron Interaction)
“Nuclear structure is governed by the fundamental laws of electromagnetism” one can find an accurate explanation of deuteron structure and binding by using my difficult differential equations that reveal the deuteron structure and give exactly the binding energy E = -2.2246 MeV. To avoid such a difficulty I present here a simple method by using the electric and magnetic forces between the distributed charges of a proton (p) and neutron (n). For example the detailed analysis of the magnetic moments and of the deep inelastic experiments gives charges -q = -5e/3 and +Q = +8e/3 limited at the centers of proton and neutron respectively, whereas the analysis gives +Q = +8e/3 distributed along the periphery of proton and -Q = -8e/3 distributed along the periphery of neutron.
Thus for a separation d (diameter) between the two-point charges at the centers of the two nucleons the application of the coulomb law gives an attractive electric force
Fe (-q, +Q) = -KqQn/d2 = - 40Ke2/9d2
Also, the charges +Q and -Q distributed along the peripheries of proton and neutron respectively yield an attractive electric force
- Fe (+Q, -Q) given by a difficult differential equation.
Since the spin is parallel we observe an attractive magnetic force
-Fm ((+Q, -Q) given by a difficult differential equation.
That is, in the simple p-n system one observes one strong attractive force between the point charges at the centers and two weak attractive forces between the peripheral charges.
However, in this simple p-n system one observes a repulsive electric force
+Fe (-q, -Q) given by a difficult differential equation, because the negative point charge -q of the proton interacts with the negative peripheral charge -Q of the neutron. In the same way, we observe a repulsive electric force
+ Fe (+Q + Q) because the positive point charge +Q of neutron interacts with the positive peripheral charge +Q of the proton. So the attractive electromagnetic force Fpn of the p-n system is given by Fpn = -40Ke2/9d2 - Fe (+Q, - Q) -Fm ( +Q,-Q) + Fe ( -q, -Q ) + Fe (+Q + Q)
Since the first force is a strong attractive force and the next attractions with the repulsions give a small net force we can take into account the binding energy E in MeV of the first force of interacting point charges by writing
40Ke/9d < 2.2246 MeV
Thus substituting the constants one gets d < 2.877/1015 m.
Unfortunately, under the discovery of the assumed uncharged neutron (2010) theoretical physicists abandoned the well-established electromagnetic laws in favor of wrong nuclear theories and models which cannot lead to the nuclear force and structure. So despite the enormous success of the Bohr model (2012) and the Schrodinger equation in three dimensions (2009), based on the well-established laws of electromagnetism neither was able to reveal the simplest structure of deuteron or the simple proton-neutron interaction. For example, the great physicists Heisenberg (2013) and Yukawa (2015) under the invalid relativity and the assumptions of the uncharged neutron developed wrong theories of the so-called strong interaction which cannot lead to the real nuclear force and nuclear structure of the simplest deuterium. Moreover after the discovery of the charged quarks (2014) Gell-Mann in 2013 under the false theories of relativity and of Yukawa did not use the well-established charge-charge interaction of the discovered charged quarks but tried to interpret the wrong strong interaction by developing his theory of quantum chromodynamics.
2.2.4. Schematic Illustration of Proton interaction Mechanisms
(a) energy loss via inelastic Coulombic interactions, (b) deflection of proton trajectory by repulsive Coulomb elastic scattering with nucleus, (c) removal of primary proton and creation of secondary particles via non-elastic nuclear interaction (p: proton, e: electron, n: neutron, γ: gamma rays).
2.3 THERAPEUTIC ABSORBED DOSE DETERMINATION
In its Report 24 on ‘Determination of Absorbed Dose in a Patient Irradiated by Beams of X or Gamma Rays in Radiotherapy Procedures’, the International Commission on Radiation Units and Measurements (ICRU) [1] concluded that “although it is too early to generalize, the available evidence for certain types of
tumor points to the need for accuracy of ± 5% in the delivery of an absorbed dose to a target volume if the eradication of the primary tumor is sought”. The ICRU continues, “Some clinicians have requested even closer limits such as ± 2%, but at the present time (in 1976) it is virtually impossible to achieve such a standard”.
These statements were made in a context where uncertainties were estimated at the 95% confidence level, and have been interpreted as if they correspond to approximately two standard deviations. Thus the requirement for accuracy of 5% in the delivery of absorbed dose would correspond to a combined uncertainty of 2.5% at the level of one standard deviation. Today it is considered that a goal in dose delivery to the patient based on such an accuracy requirement is too strict and the figure should be increased to about one standard deviation of 5%, but there are no definite recommendations in this respect.
The requirement for accuracy of ± 5% could, on the other hand, also is interpreted as a tolerance of the deviation between the prescribed dose and the dose delivered to the target volume. Modern radiotherapy has confirmed, in any case, the need for high accuracy in dose delivery if new techniques, including dose escalation in 3-D conformal radiotherapy, are to be applied. Emerging technologies in radiotherapy, for example, modern diagnostic tools for the determination of the target volume, 3-D commercial treatment planning systems and advanced accelerators for irradiation, can only be fully utilized if there is high accuracy in dose determination and delivery.
Reich [24] proposed the calibration of therapy level dosimeters in terms of absorbed dose to water, stressing the advantages of using the same quantity and experimental conditions as the user. The current status of the development of primary standards of absorbed dose to water for high energy photons and electrons and the improvement in radiation dosimetry concepts and data available have made it possible to reduce the uncertainty in the calibration of radiation beams. The development of standards of absorbed dose to water at Primary Standard Dosimetry Laboratories (PSDLs) has been a major goal pursued by the Comité Consultatif pour Les Etalons de Mesuredes Rayonnements Ionisants (Section I) [25]. Measurements of absorbed dose to graphite using graphite calorimeters were developed first and continue to be used in many laboratories. This procedure was considered as an intermediate step between air kerma and direct determination of the absorbed dose to water since absolute calorimetric measurements in water are more problematic.
Comparisons of determinations of absorbed dose to graphite were satisfactory and, consequently, the development of standards of absorbed dose to water was undertaken in some laboratories. Procedures to determine absorbed dose to water using methods to measure appropriate base or derived quantities have considerably improved at the PSDLs in the last decade. The well-established procedures are the ionization method, chemical dosimetry, and water and graphite calorimetry.
Although only the water calorimeter allows the direct determination of the absorbed dose to water in a water phantom, the required conversion and perturbation factors for the other procedures are now well known at many laboratories. These developments lend support to a change in the quantity used at present to calibrate ionization chambers and provide calibration factors in terms of absorbed dose to water, ND,w, for use in radiotherapy beams. Many PSDLs already provide ND,w calibrations at 60Co gamma-ray beams and some laboratories have extended these calibration procedures to high energy photon and electron beams; others are developing the necessary techniques for such modalities.
Also Raed: SCHOOL VARIABLES AND EFFECTIVE TEACHING OF BIOLOGY IN SECONDARY SCHOOLS
2.3.1. Distinguishing Absorbed Dose from Therapeutic Protons, External Neutrons, and Internal Neutrons
In this work, stray radiation is defined as the undesirable radiation produced from interactions between the proton beam and the components in the treatment unit or the patient. Secondary neutrons emanating from the treatment unit (or ‘external neutrons’) and within the patient (or ‘internal neutrons’) are the primary contributor to absorbed dose from stray radiation (Agosteo et al 1998, Fontenot et al 2008, Zheng et al 2008). E, HT, and Dv were calculated separately for both external and internal neutrons. However, because the MCNPX code does not directly differentiate between the absorbed dose from external versus internal radiation, the following method was used to separate the absorbed dose from each of these two components.
To isolate the absorbed dose from external neutrons, Dv, ext, the Monte Carlo system was configured to track neutrons and protons throughout the entire geometry (mode n h; imp:h, n > 0). However, all proton trajectories were terminated immediately upstream of the patient by a proton stopping plane (imp:h = 0), modeled as a very thin slab of air. Thus, in simulations with the stopping plane, only external neutrons were incident upon the patient. A type 3 mesh tally (keyword ‘total’) was used to calculate energy deposition in each anatomic voxel of the patient, and Dv, ext was calculated according to the methods described in section 2.3.
Isolating the contribution to absorbed dose from internal neutrons, Dv, int, required a slightly more complex procedure. The additional complexity was necessary because MCNPX tallies did not discriminate between therapeutic (primary) protons and protons that were liberated from inelastic nuclear reactions. First, the absorbed dose from primary protons was calculated by tracking only protons (and not neutrons) throughout the geometry (mode n h; imp:h > 0; imp:n = 0). In this case, secondary neutrons were generated, but their trajectories were immediately terminated at their points of origin. Absorbed dose was calculated in each voxel for primary protons, Dv[p1], using a type 1 mesh tally (keyword ‘pedep’). Second, a simulation was performed in which protons were tracked throughout the model but neutrons were tracked only within the patient (i.e. external neutrons were not allowed to contribute to absorbed dose). This model was identical to the previous one except that the secondary neutrons were tracked within the voxelized anatomy (imp:n > 0 in the phantom). Absorbed dose was calculated in each voxel separately for protons, Dv[p2], and neutrons, Dv[n], using type 1 rectangular mesh tallies (card ‘mesh’, keyword ‘pedep’). In the MCNPX code, the type 1 mesh tally included energy deposition only from particles that were explicitly specified on the RMESH card (e.g. ‘rmesh21:n pedep’ for neutrons). Thus, the tally excluded the proportion of energy that was deposited by other particles that were being transported, where the list of particles transported was specified on the ‘mode’ card, for example, recoil protons (Pelowitz 2005).
2.4 STRAY RADIATION
Staff radiation risk is related to the radiation field in which individuals work. Traditional protective measures focus on reducing stochastic risk. However, deterministic injury to the operator's hands cannot always be ignored. The stray radiation field is almost totally attributable to scatter from the patient. Its relative intensity is greatest near the entry port of the useful beam into the patient. The entry port moves during the procedure as the operator selects various required projections. Therefore, the relative exposure rate at any particular location in the laboratory changes with the clinical projection. The absolute scatter intensity is also dependent on the size and strength of the useful beam. Operators may put their hands near or in the useful beam. Leaded surgical gloves provide some overall finger protection for scattering fields. However, because of automatic dose rate controls, these gloves often increase risk when the operator's hands are seen on the image monitor.
Proton therapy is a promising treatment modality for some central nervous system tumors in pediatric patients. Protons have several depths–dose characteristics, such as a sharp distal fall-off versus depth in tissue, which give proton therapy a theoretical dosimetric advantage over photon radiotherapy in the sparing of nearby tissues and organs (Krejcarek et al 2007). This dosimetric advantage is especially important for children because they are more susceptible to radiation carcinogenesis, which is the radiation late effect of greatest concern. The increased susceptibility is mainly because children generally have longer expected survival times, higher relative biological effectiveness (RBE) for a given type of radiation and endpoint and smaller bodies than adults and, thus, organs that are closer to the proton field. Hence, interest in the potential use of proton therapy for children with cancer is increasing (cf Archambeau et al 1992, Miralbell et al 1997, 2002, Lin et al 2000, Noel et al 2003, Kirsch and Tarbell 2004, St Clair et al 2004, Yuh et al 2004, Lee et al 2005, Lundkvist et al 2005, Mu et al 2005).
Proton beam radiotherapy unavoidably exposes healthy tissue to stray radiation emanating from the treatment unit and secondary radiation produced within the patient. These exposures provide no known benefit and may increase a patient's risk of developing radiogenic cancer.
Several studies have examined the stray radiation exposures associated with proton therapy (Agosteo et al 1998, Schneider et al 2002, Yan et al 2002, Jiang et al 2005, Polf and Newhauser 2005, Polf et al 2005, Hall 2006, Wroe et al 2007, Zheng et al 2007a, 2007b, 2008), and a few investigations have estimated stray neutron exposures in humanoid phantoms (Fontenot et al 2008, Zacharatou Jarlskog et al 2008, Taddei et al 2008). Miralbell et al (2002) reported a treatment planning study in which the risks of second cancer were compared for proton therapy versus photon therapy following craniospinal irradiation (CSI); the risks from neutron radiation were neglected. Newhauser et al (2009) supplemented the analysis from Mirabell et al to include neutron radiation. Absorbed dose from neutrons is of particular concern because, although the absorbed dose is less, RBE of neutrons (including their secondary particles) is generally greater than that of protons, photons, and electrons. They predicted a stray radiation dose using an adult-sized anthropomorphic phantom. Mirabell et al found that proton therapy carried lower predicted risk of second cancer; Newhauser et al reported that consideration of neutrons increased the risk of second cancer, but proton therapy still carried a lower risk than photon therapy. The results of Miralbell et al and Newhauser et al were based on one patient, a 6-year-old boy, and the dosimetric uncertainties were large and difficult to estimate. Hence, there is a need for additional, independent investigations, particularly with more realistic dose predictions and for patients of other ages.
2.5 SHIELDING DESIGN
Shielding is an important part of the cancer center design. Early planning and regular communication can reduce costly errors. Alternatives to concrete shielding can offer many benefits.
Advanced shielding techniques include:
- Modular shielding
- Rapidly constructed cancer centers
- Advanced shielded doors
Getting the correct shielding in the correct locations is an important consideration in radiotherapy center design.
It typically requires coordination between
- Physicists
- Architects
- Facility owners
- Equipment vendors
- MEP engineers
- Structural engineers
- Other stakeholders (e.g. doctors, interior designers, etc)
Regular communication between these groups is essential to minimize mistakes and ensure an accurate shielding design.
Since shielding mistakes can be costly to fix, many projects can benefit from having an experienced shielding specialist on their design team.
2.5.1. Shielding Design Parameters
The shielding design is usually done by one or more physicists.
Their design is based on:
Their design is based on:
- The type of equipment in the facility
e.g. a dual-energy 6/15MV linear accelerator with the high-dose-rate option
- The regulated permissible doses allowed outside the shielding
e.g. NCRP 151 guidelines
- The anticipated usage of the equipment
e.g. 20 patients per day vs 50 patients per day
- The types of spaces outside the shielding
e.g. an office vs a parking lot vs a stairwell
- Any space constraints that affect the shielding
e.g. the room must be fit within a 15’-0” high space
2.5.1. Design Considerations - Equipment
Machine type
This dictates important design factors such as the minimum size of the room, the penetrations into the room, etc.
Vendors produce documents detailing design requirements for each of their machine models. These documents are often referred to as:
DDR - Designer’s Desk Reference. IDP - Installation Data Package.
BID - Building Interface Document. SPG - Site Planning Guide
2.5.3. Design Considerations - Clearances
Space clearances and obstructions
Fitting shielding into a small space requires thinner, more expensive shielding materials. Similarly avoiding obstacles (e.g. ceiling soffits, structural columns) can complicate the shielding design.
These might be unavoidable when constructing a bunker inside an existing building but if the building is a new build, giving early thought to the shielding can save money. To keep costs low, provide ample space for shielding, free of any columns or other obstructions.
2.5.4. Design Considerations - Location
The location of the bunker within the facility can affect the price:
- Keeping the bunker on-grade will eliminate the need for floor shielding.
A subterranean vault with earth-backing on one or more walls will reduce the amount of shielding required and lower overall costs of the design.
- Building bunkers next to each other shares the shielding and reduces costs.
There is a recent trend to build bunkers not on-grade. This requires floor shielding and attention to the structural loads imposed on the building. A modular vault can impose fewer loads on the building than poured concrete.
2.5.5. Advances in Shielding Design
Modular shielding
Pre-fabricated modular shielding, control module, and service modules –Constructed offsite and installed by crane Shielding packs can be adjusted, removed or reused. Comparative concrete construction would take months and cannot be altered or reused.
Common Trends
Shielding one room for two purposes
Example 1: Brachytherapy room to be used as a future linac.
Example 2: Installing a low energy linac now and a high energy machine in the future.
Need to think about:
- Space requirements for each machine type
- Amount and location of shielding needed for each type
- Foundation requirements if adding shielding in the future
Upgrading a machine in an existing vault
e.g. Changing an old linac room to a new Cyberknife treatment room.
Need to think about:
- Demolition requirements – will the new machine fit?
- Option to change from maze-entry to direct-entry by removing the maze wall.
- New shielding and space requirements – does the new machine require additional shielding?
- Amount of down-time due to renovations – how quickly can the upgrade be completed?
Will there be lost revenue?
Will there be lost revenue?
Crane-able wall sections
Build a vault in 5 days
Bi-parting direct-entry doors
Fastest doors in the world
Modular interiors
Dust-free re-design
Also Read: EXAMINING THE PERCEPTIONS OF READERS ON THE CONTRIBUTION OF THE DAILY NATION’S PEACE MESSAGES TO THE 2013 ELECTIONS
CHAPTER THREE
3.1 PROTON THERAPY
In the field of medical procedures, Proton therapy, or proton beam therapy is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The chief advantage of proton therapy over other types of external beam radiotherapy is that as a charged particle the dose is deposited over a narrow range and there is minimal exit dose.
3.1.2. Description
Proton therapy is a type of external beam radiotherapy that uses ionizing radiation. In proton therapy, medical personnel uses a particle accelerator to target a tumor with a beam of protons. These charged particles damage the DNA of cells, ultimately killing them or stopping their reproduction. Cancerous cells are particularly vulnerable to attacks on DNA because of their high rate of division and their reduced abilities to repair DNA damage. Some cancers with specific defects in DNA repair may be more sensitive to proton radiation.
Because of their relatively large mass, protons have little lateral side scatter in the tissue; the beam does not broaden much, stays focused on the tumor shape and delivers only low-dose side effects to surrounding tissue. All protons of a given energy have a certain range; very few protons penetrate beyond that distance. Furthermore, the dose delivered to tissue is maximized only over the last few millimeters of the particle’s range; this maximum is called the Bragg peak, often referred to as the SOBP.
To treat tumors at greater depths, the proton accelerator must produce a beam with higher energy, typically given in eV or electron volts. Accelerators used for proton therapy typically produce protons with energies in the range of 70 to 250 MeV. Adjusting proton energy during the treatment maximizes the cell damage the proton beam causes within the tumor. Tissue closer to the surface of the body than the tumor receives reduced radiation, and therefore reduced damage. Tissues deeper in the body receive very few protons, so the dosage becomes immeasurably small.
In most treatments, protons of different energies with Bragg peaks at different depths are applied to treat the entire tumor. These Bragg peaks are shown as thin blue lines in the figure to the right. The total radiation dosage of the protons is called the spread-out Bragg peak (SOBP), shown as a heavy dashed blue line in the figure to the right. It is important to understand that, while tissues behind (or deeper than) the tumor receives almost no radiation from proton therapy, the tissues in front of (shallower than) the tumor receives radiation dosage based on the SOBP.
3.2 CYCLOTRON PARTICLE ACCELERATION
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1934 in which charged particles accelerate outwards from the center along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field. Lawrence was awarded the 1939 Nobel prize in physics for this invention. Cyclotrons were the most powerful particle accelerator technology until the 1950s when they were superseded by the synchrotron, and are still used to produce particle beams in physics and nuclear medicine. The largest single-magnet cyclotron was the 4.67 m (184 in) synchrocyclotron built between 1940 and 1946 by Lawrence at the University of California at Berkeley, which could accelerate protons to 730 MeV. The largest cyclotron is the 17.1 m (56 ft) multi magnet TRIUMF accelerator at the University of British Columbia in Vancouver, British Columbia which can produce 500 MeV protons. Over 1200 cyclotrons are used in nuclear medicine worldwide for the production of radionuclides.
A cyclotron accelerates a charged particle beam using a high-frequency alternating voltage which is applied between two hollow "D"-shaped sheet metal electrodes called "dees" inside a vacuum chamber.[23] The dees are placed face to face with a narrow gap between them, creating a cylindrical space within them for the particles to move. The particles are injected into the center of this space. The dees are located between the poles of a large electromagnet which applies a static magnetic field B perpendicular to the electrode plane. The magnetic field causes the particles' path to bend in a circle due to the Lorentz force perpendicular to their direction of motion.
If the particles' speeds were constant, they would travel in a circular path within the dees under the influence of the magnetic field. However, a radio frequency (RF) alternating voltage of several thousand volts is applied between the dees. The frequency is set so that the particles make one circuit during a single cycle of the voltage. To achieve this, the frequency must match the particle's cyclotron resonance frequency: F=qB/2Ï€m, where B is the magnetic field strength, q is the electric charge of the particle, and m is the relativistic mass of the charged particle. Each time after the particles pass to the other dee electrode the polarity of the RF voltage reverses. Therefore, each time the particles cross the gap from one dee electrode to the other, the electric field is in the correct direction to accelerate them. The particles' increasing speed due to these pushes causes them to move in a larger radius circle with each rotation, so the particles move in a spiral path outward from the center to the rim of the dees. When they reach the rim a small voltage on a metal plate deflects the beam so it exits the dees through a small gap between them, and hits a target located at the exit point at the rim of the chamber, or leaves the cyclotron through an evacuated beam tube to hit a remote target. Various materials may be used for the target, and the nuclear reactions due to the collisions will create secondary particles which may be guided outside of the cyclotron and into instruments for analysis.
The cyclotron was the first "cyclical" accelerator. The advantage of the cyclotron design over the existing "electrostatic" accelerators of the time such as the Cockcroft-Walton accelerator and Van de Graaff generator, was that in these machines the particles were only accelerated once by the voltage, so the particles' energy was equal to the accelerating voltage on the machine, which was limited by air breakdown to a few million volts. In the cyclotron, in contrast, the particles encounter the accelerating voltage many times during their spiral path, and so are accelerated many times,[2] so the output energy can be many times the accelerating voltage.
The largest particle accelerators have dimensions measured in miles. A cyclotron is a particle accelerator that is so compact that a small one could actually fit in your pocket. It makes use of electric and magnetic fields in a clever way to accelerate a charge in a small space.
A cyclotron consists of two D-shaped regions known as dees. In each dee, there is a magnetic field perpendicular to the plane of the page. In the gap separating the dees, there is a uniform electric field pointing from one dee to the other. When a charge is released from rest in the gap it is accelerated by the electric field and carried into one of the dees. The magnetic field in the dee causes the charge to follow a half-circle that carries it back to the gap.
While the charge is in the dee the electric field in the gap is reversed, so the charge is once again accelerated across the gap. The cycle continues with the magnetic field in the dees continually bringing the chargeback to the gap. Every time the charge crosses the gap it picks up speed. This causes the half-circles in the dees to increase in radius, and eventually, the charge emerges from the cyclotron at high speed.
How can you time it so the electric field reverses direction at the right time to accelerate the charge properly? Recall that for a charge following a circular path in a uniform magnetic field, the period is independent of the speed of the charge. Every half-circle in the dees takes the same amount of time. Unlike the cyclotron in the simulation, a real cyclotron is set up with a small gap so that the time to cross the gap is much smaller than the time spent in a dee. Hooking the dees up to an AC voltage source that reverses direction at regular intervals (corresponding to the time the charge takes to do a half-circle in a dee) is all that is required to produce an electric field that reverses direction at the appropriate time.
Also Raed:
TOTEMS AND TABOOS; ITS VALUES AND SIGNIFICANCE
3.2.1 THE ROLE OF PARTICLE ACCELERATORS COMBATING CANCER
At the beginning of the third millennium, one European citizen out of three will have to deal with a cancer episode in the course of his/her life. Worldwide the estimated number of new cancer cases each year is expected to rise from 10 million in 2000 to 15millions by 2020. Cancer is currently the cause of 12% of all deaths worldwide. Within the European Union, it is over 1,5 million new cancer cases that are diagnosed every year and over 920000 people die of cancer with the two leading cause of cancers in Europe are Breast and Prostate. Therefore combating cancer is a major societal and economic issue for Europe and to face up these new challenges strong mobilization among the scientific community and industrial manufacturers is needed.
Today’s approaches to treat cancer are the surgical removal of the tumor tissue, radiotherapy, chemotherapy, and immunotherapy. Most scientists are confident that in the long run, significant improvements in cancer cure will come from immunotherapy and/or gene therapy and drug targeting; research towards such systemic treatments is and will be of the utmost importance. However, in the meantime, radiotherapy either combined with surgery or as the main treatment modality still remains the most effective technique to treat cancer.
More than half of all cancer patients are now treated by radiation therapy thanks to the technical progress made with irradiation equipment in the last ten years. For external radiation therapy (RT), for instance, high energy photon or electron beams are mainly produced by linear accelerators, while a very limited number of proton synchrotrons or cyclotrons are used for the treatment of cancers close to vulnerable organs such as the eyes and the optical and auditory nerves, spinal cords. For internal radiation therapy, brachytherapy, radioactive sources are put in the tumor with undeniable advantages for the patient in given situations. In an abstract from Annex A of "Europe Against Cancer" [2] in 2014, the present status of cured patients following a specific treatment shows that in Europe at present 45% of all the treated patients are "cured", which means that these patients have a symptom-free survival period exceeding five years. About 90% of the cured patients (i.e. 40% of the total) are cured because of loco-regional control of the primary tumor, i.e. because of surgery and radiotherapy. Of course, the treatments are almost always accompanied by chemotherapy to prevent the spreading of metastasis. In fact, surgery and radiotherapy alone are successful in 22% and 12% of the cases respectively. When combined, they account for another 6% of the cases so that radiotherapy is involved in almost half of the curative treatments of loco-regional type. Despite a widespread belief, all the other systemic treatments account for 5% only of the cured patients. There is ample space for improvements here because 37 % of the tumors are metastatized at the moment of diagnosis and cannot be cured with loco-regional treatments alone.
Three strategic approaches are generally proposed:
• Early detection and improved diagnosis based on widespread screening to reduce the number of late diagnoses.
• Improved local treatment, avoiding poor treatments, to treat tumors with difficult localisations and tumors which are radio-resistant to conventional radiotherapy.
• Improved systemic treatments combined with local treatments that can reduce the tumor mass significantly.
3.3 PROCEDURES
3.3.1. How proton therapy works
A machine called a synchrotron or cyclotron speeds up the protons. The protons’ speed determines the energy level. High-energy protons travel deeper in the body than low-energy ones.
The protons go to the targeted place in the body. There, they deposit the specific radiation dose in the tumor.
With proton therapy, radiation does not go beyond the tumor. In contrast, with photon-based external-beam radiation therapy, x-rays continue depositing radiation as they exit the body. This means that the radiation leaving the body may damage nearby healthy tissue. That damage can cause side effects.
3.3.2. What to expect
You typically receive proton therapy in an outpatient setting. This means treatment does not require staying overnight in a hospital.
The number of treatment sessions depends on the type and stage of cancer. Sometimes, patients receive proton therapy in 1 to 5 treatments. Typically, this is called stereotactic body radiation therapy. If a person receives a single, large radiation dose, it is sometimes called radiosurgery.
3.3.3. Treatment planning
Like other external-beam radiation therapy technologies, proton treatment requires planning. Before treatment, you have a specialized computed tomography (CT) or magnetic resonance imaging (MRI) scan. During this scan, you are on a table in the same position as during treatment. This may require an immobilization device.
3.3.4. Immobilization devices
An immobilization device restricts movement. The type of device depends on the tumor’s location. For example, you may need to wear a custom-made mask for the treatment of a tumor in the eye, brain, or head. This ensures the radiation accurately targets the tumor during each treatment.
3.3.5 Comfort wearing an immobilization device
Immobilization devices are designed to fit snugly. This prevents motion during radiation treatment. However, the radiation oncology team cares about your comfort. Talk with the team to find a comfortable, reproducible treatment position. Your doctor may prescribe medication to help you relax if you feel anxiety lying still in an immobilizing device.
3.3.6. Receiving Treatment
Treatment is delivered in a special room. Members of the team will place you on the treatment table using an immobilization device if needed.
The treatment team aligns lasers to aim radiation at the marked site. Before treatment, you receive another x-ray or CT scan. This ensures that you are in the correct position. These pretreatment images or target-tracking images are often critical for accurate radiation therapy. Talk with your doctors about whether the proton therapy you are receiving uses these advanced imaging technologies.
Some proton treatment rooms deliver proton beams through a gantry. A gantry can rotate and deliver radiation therapy from the angle prescribed by your doctor. Your team members will move the gantry to the desired position before treatment.
Then, the radiation oncology treatment team leaves the room. Team members see, hear, and communicate with you through audio/video equipment. They use controls outside the room to give you proton therapy.
Protons leave the cyclotron or the synchrotron machine. Magnets then direct them to the tumor, sometimes using the gantry. During this time, you must stay still to avoid moving the tumor out of the proton beam.
3.3.7. The time needed for each treatment
Typically, treatment lasts about 15 to 30 minutes once you enter the treatment room. However, these times vary based on several factors:
- The part(s) of the body receiving treatment
- The number of treatment segments
- The number of x-rays or CT scans done during the positioning process
Ask your treatment team about how long treatment will take. Sometimes, you may receive several segments from different gantry angles. If so, ask whether someone will enter the room between segments to reposition the gantry. In some cases, the team rotates the gantry remotely.
Proton beam availability may also affect timing. Most facilities have only one proton cyclotron or synchrotron. So you may need to wait a few minutes until another patient finishes treatment.
3.3.8. How to Use a Cyclotron Particle Accelerator to Fight Cancer
Step 1
CYCLOTRON
The magnet-packed particle accelerator weighs 220 tons but is only 18 feet wide and 8 feet high.
Step 2
BEAM LINE
Protons moving at almost the speed of light are deflected and focused by magnets along the line. The beamlines are kept in a vacuum so that the particles don't slow down. The line branches to up to five separate treatment rooms.
Step 3
GANTRIES
These 90-ton machines aim the proton beam at the patient's body; the relatively heavy particles slow down when they encounter body tissue. When they move more slowly they interact with atoms in the body, producing ionizing radiation. Doctors can adjust the strength of the beam to cause the protons to produce radiation only at the tumor's location.
3.3.9. Radiation treatments for cancer are double-edged swords: They indiscriminately destroy healthy tissue along with cancer cells, causing debilitating side effects. To target cancer cells alone, the University of Pennsylvania is opening a next-generation treatment facility that uses high-energy proton beams to deliver pinpoint strikes.
Penn's $144 million Roberts Proton Therapy Center will use magnets to accelerate protons to near light speed in a 220-ton cyclotron. The beamlines direct the proton beams into treatment rooms where patients will have their tumors zapped. Nozzles on the ends of 90-ton gantries, aided by the CT, MRI and PET imaging equipment, aim the beams. The proton beam works like any other form of ionizing radiation, which destroys cancer cell DNA and prevents replication. "The difference is all in the physical characteristics of the beam itself," explains James Metz, chief of clinical operations of the new facility. "A regular X-ray goes on one side of the body and out the other side and irradiates everything in between." But unlike the massless photons that compose X-rays, protons are heavy particles that enter the body without much scattering, so they can be aimed with precision. They also continue in a straight line as they slow, releasing radioactive energy at a location determined by the beam's energy. "What that means for the patient is a much lower dose in front of the tumor and absolutely no radiation behind the tumor," Metz says.
3.4. TREATMENT AND USES
3.4.1 Proton Therapy
Physicians use protons to treat conditions in two broad categories:
- Disease sites that respond well to higher doses of radiation, i.e., dose escalation. In some instances, dose-escalation has demonstrated a higher probability of "cure" (i.e., local control) than conventional radiotherapy. These include, among others, uveal melanoma (ocular tumors), skull base and paraspinal tumors (chondrosarcoma and chordoma), and unresectable sarcomas. In all these cases proton therapy achieves significant improvements in the probability of local control over conventional radiotherapy. In the treatment of ocular tumors, proton therapy also has high rates of maintaining the natural eye.
- Treatments where proton therapies increased precision reduce unwanted side effects by lessening the dose to normal tissue. In these cases, the tumor dose is the same as in conventional therapy, so there is no expectation of an increased probability of curing the disease. Instead, the emphasis is on reducing the integral dose to normal tissue, thus reducing unwanted effects.
Two prominent examples are pediatric neoplasms (such as medulloblastoma) and prostate cancer.
Pediatric treatments
In the case of pediatric treatments, a 2004 review gave theoretical advantages but did not report any clinical benefits.
Prostate cancer
In prostate cancer cases, the issue is less clear. Some published studies found a reduction in long term rectal and genito-urinary damage when treating with protons rather than photons (meaning X-ray or gamma-ray therapy). Others showed a small difference, limited to cases where the prostate is particularly close to certain anatomical structures. The relatively small improvement found may be the result of inconsistent patient set-up and internal organ movement during treatment, which offsets most of the advantage of increased precision. One source suggests that dose errors around 20% can result from motion errors of just 2.5 mm (0.098 in). and another that prostate motion is between 5–10 mm (0.20–0.39 in).
However, the number of cases of prostate cancer diagnosed each year far exceeds those of the other diseases referred to above, and this has led some, but not all, facilities to devote a majority of their treatment slots to prostate treatments. For example, two hospital facilities devote roughly 65% and 50% of their proton treatment capacity to prostate cancer, while a third devotes only 7.1%.
Overall worldwide numbers are hard to compile, but one example states that in 2003 roughly 26% of proton therapy treatments worldwide were for prostate cancer.
Eye tumors
Proton therapy for ocular (eye) tumors is a special case since this treatment requires only comparatively low energy protons (about 70 MeV). Owing to this low energy requirement, some particle therapy centers only treat ocular tumors.[ Proton, or more generally, hadron therapy of tissue close to the eye affords sophisticated methods to assess the alignment of the eye that can vary significantly from other patient position verification approaches in image-guided particle therapy. Position verification and correction must ensure that the radiation spares sensitive tissue like the optic nerve to preserve the patient’s vision.
3.4.2. Uses of Cyclotrons
For several decades, cyclotrons were the best source of high-energy beams for nuclear physics experiments; several cyclotrons are still in use for this type of research. The results enable the calculation of various properties, such as the mean spacing between atoms and the creation of various collision products. Subsequent chemical and particle analysis of the target material may give insight into the nuclear transmutation of the elements used in the target.
Cyclotrons can be used in particle therapy to treat cancer. Ion beams from cyclotrons can be used, as in proton therapy, to penetrate the body and kill tumors by radiation damage, while minimizing damage to healthy tissue along their path. Cyclotron beams can be used to bombard other atoms to produce short-lived positron-emitting isotopes suitable for PET imaging. More recently some cyclotrons currently installed at hospitals for radioisotopes production have been retrofitted to enable them to produce technetium-99m. Technetium-99m is a diagnostic isotope in short supply due to difficulties at Canada's Chalk River facility.
3.5. CHALLENGES AND THE FUTURE OF PROTON THERAPY
In the last few decades, proton therapy has transitioned from research laboratories into the clinical setting – making this publication particularly timely. There are currently around 60 proton therapy facilities worldwide, and this number is increasing rapidly. “Proton therapy is becoming a standard treatment option but there are still many challenges in terms of the physics, biology and clinical use of protons, which are summarized in this ebook,” Paganetti explains.
3.5.1. CHALLENGES OF PROTON THERAPY
Challenges associated with proton therapy, starting off with the technical issues involved in setting up a proton therapy facility.
Proton therapy is a type of external beam radiotherapy, and shares risks and side effects of other forms of radiation therapy. However, the dose outside of the treatment region can be significantly less for deep-tissue tumors than X-ray therapy, because proton therapy takes full advantage of the Bragg peak. Proton therapy has been in use for over 40 years and is a mature treatment technology. However, as with all medical knowledge, understanding of the interaction of radiation (proton, X-ray, etc.) with tumor and normal tissue is still imperfect.
Proton therapy drawbacks:
- Proton therapy effectively treats only certain cancer types.
- More research on the potential benefits of proton therapy is needed to fully understand how it compares with other advanced external beam radiation therapy methods.
- Proton therapy requires highly specialized, expensive equipment. This means it is available at a few medical centers in the United States.
- It may cost more than conventional radiation therapy. Insurance provider rules about what is covered by insurance and how much patients need to pay to vary. Talk with your insurance provider to learn more.
3.5.2. THE FUTURE OF PROTON THERAPY
The first hospital-based proton therapy center in the United States, at Loma Linda University in southern California, was recently renamed to honor the man who helped launch the site in 1990: Dr. James M. Slater. Slater, a radiation oncologist, recently spoke to DOTmed News about new directions for proton technology and why it needs to become more competitive with conventional radiation therapy.
New Frontier
Proton therapy is typically used to treat cancer, but Slater envisions a new frontier: central nervous system disorders. To start, his team is looking to treat epilepsy to help both young children who suffer from severe forms of the disease and veterans who developed epilepsy as a result of head injuries during their time in the service.
Proton therapy is typically used to treat cancer, but Slater envisions a new frontier: central nervous system disorders. To start, his team is looking to treat epilepsy to help both young children who suffer from severe forms of the disease and veterans who developed epilepsy as a result of head injuries during their time in the service.
But epilepsy presents a two-fold problem. First, the team has to develop an advanced imaging technique, likely using PET/CT in conjunction with MRI, to pinpoint the origin of the abnormal signals in the brain that cause muscle contractions. Then, the team has to develop a technique for precisely ablating it using protons.
“We can tell from EEGs and other ways roughly were (the signal source) is, but not near well enough to treat with a very small beam,” Slater says. “That’s why we’re working on imaging in one lab, and another is working on making the beam shape and design.”
Slater envisions one-day treatments for most patients, as the brain structure needing to be destroyed is likely much smaller than most tumors. But Slater says his team will have a better understanding of the project soon. Animal studies will likely start this summer, with preliminary data coming probably before the end of the year. “We ought to be able to get it and know by the end of the year whether it can be done,” he says. “Right now, no one knows.”
Slater envisions one-day treatments for most patients, as the brain structure needing to be destroyed is likely much smaller than most tumors. But Slater says his team will have a better understanding of the project soon. Animal studies will likely start this summer, with preliminary data coming probably before the end of the year. “We ought to be able to get it and know by the end of the year whether it can be done,” he says. “Right now, no one knows.”
Fewer fractions, more competitive
The physical properties of proton therapy — it deposits a dose in a precise volume, and can spare more healthy surrounding tissue from radiation — means using it in the treatment of rare pediatric brain cancers is relatively uncontroversial. But the growth in treatments for prostate cancer, for which Medicare can pay $50,000 a treatment, has drawn criticism, mostly because of the lack of studies showing it leads to better outcomes than other, cheaper forms of radiation therapy.
But Slater says that as proton therapy advances and providers become more experienced, the modality can become more competitive. And it can do this by reducing the number of fractions — or visits — required to treat a patient.
“When protons get up to par, to where they should be, we won’t have these long weeks of treatment,” he says.
When he began in the early days, Slater says fractions were similar to X-rays, around eight weeks long. But now his group is working on reducing that protocol to four or five weeks.
“Some of them have been cut roughly in half, but it’s going to go less than that. The small (tumors) will probably be just like we’re doing on the brain, one day, one treatment,” Slater says. “Most of the people who go into protons know that this will be a thing of the future and admit they need to get that (fractions) down,” he adds.
“Some of them have been cut roughly in half, but it’s going to go less than that. The small (tumors) will probably be just like we’re doing on the brain, one day, one treatment,” Slater says. “Most of the people who go into protons know that this will be a thing of the future and admit they need to get that (fractions) down,” he adds.
CHAPTER FOUR
SUMMARY, CONCLUSION, AND RECOMMENDATION
4.1 SUMMARY
Radiation therapy is one of the most frequently used methods for treating cancer patients. Therefore improving the quality of the treatment by using new irradiation technologies is one of the radiotherapist's constant concerns. The use of accelerators for delivering protons, heavier charged particles and secondary beams such as neutrons brings further improvement in dose distribution and in interesting biological properties for radiations producing a high Linear Energy Transfer (LET).
Cyclotrons have been present in this field since the early history of radiotherapy and they could play a major role in future dedicated hospital-based facilities which include not only an accelerator but also specific beam-transport and beam-delivery systems. Modern cyclotron technology exists today to meet all of the requirements within a reasonable budget. Specific performances and several cyclotron designs are presented.
4.2 CONCLUSIONS
Cyclotrons are good candidates for radiotherapy with heavy particles. As is well known a cyclotron is capable of accelerating large intensities. Therefore isochronous cyclotrons are well-suited accelerators for neutron therapy. Moreover, for proton therapy the acceleration takes only 10 to 20 microseconds (typical value), so the beam can be turned on and off rapidly by acting on the low energy end of the machine (external injection line if any or ion source). Furthermore, dynamic control of the intensity can be easily realized. The system is safe because in the case of a failure or danger condition the beam can be turned off in less than 20 microseconds by cutting the injected beam. During this delay, the patient would receive at most one-millionth of the standard dose. Costs saving; A standard proton therapy facility based on a cyclotron (small footprint of the equipment) reduces the cost of the building. To this end a superconducting cyclotron in addition to a compact gantry is attractive. Besides, the running costs are reduced when using a superconducting coil (total power in the magnet about 30 kW). Controls and operation: easy and cheap; A fixed frequency isochronous cyclotron, giving fixed energy to the accelerated ions, is a simple accelerator to operate: a PC is sufficient to tune and control the cyclotron.
4.3 RECOMMENDATION
For promotion and support the spreading of the medically dedicated particle accelerator facility and technology, the AG recommends that:
1. The Agency should consider organizing seminars, regular meetings and CRPs on topics relevant to technological developments of proton therapy, such as:
• Quality Assurance program for proton (and heavy-ion) therapy facility,
• Respiratory-gated irradiation technique for radiation therapy,
• beam scanning technique for conformal dose delivery,
• dosimetry intercomparison,
• Regional needs for proton therapy facilities.
2. The Agency should promote and support to make a standard QA program. Even if they used a different type of facility and technique, it would be necessary to assure the basic specification of the treatment beam and peripheral devices.
3. The Agency should utilize all appropriate funding avenues to support the education and training of medical physicists, medical doctors and radiological technicians in developing countries either at regional accelerator centers or elsewhere as appropriate. Some short courses may be organized at convenient locations for a better understanding of the sophisticated proton or ion beam therapy. Clearly, much relevant training has to take place at established facilities.
4. The Agency should strengthen the mechanism for partial support for personnel from developing countries to attend the related meeting, such as PTCOG.
5. The Agency should strengthen its collaboration with PTCOG meetings.
For Similar Article Click Here
REFERENCES
Agosteo S, Birattari C, Caravaggio M, Silari M, Tosi G. Secondary neutron and photon dose in proton therapy. Radiother Oncol. 1998;48:293–305. [PubMed]
Anferov V, Collins J, Friesel DL, Katuin J, Klein SB, Nichiporov D, Wedekind MW. The Indiana university proton therapy system 10th European Particle Accelerator Conf. Edinburgh, UK: EPAC; 2006. pp. 2349–51.
Archambeau JO, Slater JD, Slater JM, Tangeman R. Role for proton beam irradiation in the treatment of pediatric CNS malignancies. Int J Radiat Oncol Biol Phys. 1992;22:287–94. [PubMed]
B. Gottschalk and M.S. Wagner, "Contoured scatterer for proton dose flattening", Harvard Cyclotron Laboratory, a preliminary report 3/29/89 (1989)
Brenner DJ, Hall EJ. Secondary neutrons in clinical proton radiotherapy: a charged issue. Radiother Oncol. 2008;86:165–70. [PubMed]
C. Tobias, H. Anger, and J. Lawrence, "Radiobiological use of high energy deuterons and alpha", American Journal of Roentgenology 67: 1(1952).
C. Tobias, J. Roberts and J. Lawrence, "Irradiation hypophysectomy and related studies using 340 MeV p and 190 MeV d" Proceedings of the Int. Conf. on Peaceful uses of Atomic Energy held in Geneva in the United Nations.
E. Pedroni et al., The 200 MeV proton therapy project at PSI: conceptual design and practical realization, to be published in Medical Physics, NS 94022
F. Farley, Oral presentation: "Supertwist gantry and dynamic beam spreading". XIXth PTCOG, October 31 to November 2, 1993, Cambridge, Mass., USA.
F. Farley, private communication.
Fontenot JD, Newhauser WD, Bloch C, White RA, Titt U, Starkschall G. Determination of output factors for small proton therapy fields. Med Phys. 2007;34:489–98. [PubMed]
Fontenot JD, Newhauser WD, Titt U. Design tools for proton therapy nozzles based on the double-scattering foil technique. Radiat Prot Dosim. 2005;116:211–5. [PubMed]
Fontenot JD, Taddei P, Zheng Y, Mirkovic D, Jordan T, Newhauser WD. Equivalent dose and effective dose from stray radiation during passively scattered proton radiotherapy for prostate cancer. Phys Med Biol. 2008;53:1677–88. [PubMed]
H. G. Blosser et al., Proposal for a manufacturing prototype superconducting cyclotron for advanced cancer therapy, NSCL-MSU, February 1993.
H. G. Blosser, 1988 Annual report of the National Superconducting Cyclotron Laboratory, Michigan State University, p. 107.
H.N. Jungwirth and J.G. de Villiers, 13th Int. Conf. on Cyclotrons and their Applications, Vancouver 1992, 709-712.
M. Catteral, "Fast neutrons in oncology", British Journal of Hospital Medicine, 12,853-860 (1974)
P. Mandrillon and F. Farley, Cyclotrons as a booster for high energy proton therapy, to be published.
P. Mandrillon et al., A compact facility for high energy proton therapy based on a superconducting cyclotron, to be presented at EPAC 94 in London.
P. Mandrillon et al., Commissionong and implementation of the MEDICYC Cyclotron program, 12th Int. Conf. on Cyclotrons and their applications, Berlin, May 89.
R. Stone, J. Lawrence, and P. Aebersold, "Preliminary report on the use of fast neutrons treatment of malignant disease" Radiology 35: 322-327 (1940)
R. Wilson "Radiological use of fast protons "Radiology 47, 487 (1946).
Y. Jongen et al., "Cyclotron based proton therapy system including a new design of large throw gantries", to be published in the Proc. of the Como Conference on hadron therapy.
No comments