Proton Therapy: A Positive Subject
Katie N. Copeland
University of Alabama at Birmingham
Abstract
Radiation therapy is a very important part of treating most cancer patients. While conventional photon therapy is the mainstream form of radiation, researchers are expanding the field to include other forms of radiation, including protons, neutrons, and ions. Proton therapy specifically has the attention of many radiation oncology professionals. Protons are a key element in conventional and modern science. There are definite advantages to when protons are applied to radiation therapy. They have a near perfect dose distribution that leaves an absence of side effects, which is a very important factor with any cancer treatment. With the patient as the first priority, this would impact them and improve their treatment experience greatly. With these clear benefits, proton therapy is so little known because the facilities, treatments, and research are very expensive. As proton therapy proves itself and becomes more efficient and affordable, it may gradually make its way into cancer centers around the world with the ability to fight cancer in a more productive way than has ever been seen.
There are several serious diseases that plague the world and claim the lives of millions of people each year. In America, the top three conditions are cardiovascular disease, cancers, and diabetes.1 Specifically, cancer is a brutal disease that is all too common in today’s society. Everyone knows someone who has been diagnosed with this disease. Healingwithnutrition.com estimates that one in three Americans will get cancer in their lifetime.1 That is a discouraging number that makes you, the reader, at great odds of acquiring the disease. Focus is placed on reducing this number and eventually winning the battle against cancer.
Surgery, chemotherapy, and radiation therapy are the first line treatments of cancer. Lesser known options include hormone therapy, oxygen therapy, and alternative medicine. Radiation therapy is the fastest growing cancer treatment technology. It is always used when it is an option because unlike surgery, it provides a noninvasive form of treating the cancer cells. It often has less brutal side effects than chemotherapy because radiation is localized to the tumor location while chemotherapy affects the entire body. For these reasons, radiation therapy is often a favored form of treatment. When one thinks of radiation therapy, it is often generalized as using photon irradiation to treat the tumor. Photon irradiation uses x-ray radiation, which is no mass and has no charge, to interact with the nucleus of the cancer cells to disrupt their growth.2 This disruption can lead to death of the cell which leads to death of the cancer. X-rays are easy and cheap to produce, making this treatment economical and efficient. While this is the most widely used form of radiation therapy, focus and research is being shifted to particle therapy, which uses protons, neutrons, and heavy ions. Particle therapy works in a similar manner as x-rays, except since they are bigger and more powerful, they can destroy the DNA worse than x-rays, which often ruins the ability of the cell to repair itself.2 Proton therapy is one form of the most common forms of particle therapy and will likely be part of future generations of radiation therapy.
The proton has always been evident in the scientific world. Atoms are the building blocks of cells, and cells are the building blocks of human life. A proton is one of the main particles of an atom, along with the neutron and electron. Protons are made up of smaller particles called quarks. There are two “up” quarks and one “down” quark.3 They carry a positive charge and are large in mass, about two thousand times the size of an electron. They are located in the nucleus with neutrons, with the electrons orbiting outside the nucleus.3 Protons have had key uses in science and are now expanding their way to greater uses such as treating cancer. However, the idea of using protons in radiation oncology is not a new one.
For over a century, studies and experiments have taken place to explore radiation and the effects it can have. It all began in 1895 when Wilhelm Rontgen discovered x-rays.4 This discovery led to the identification of basic chemical elements throughout the early 1900’s. In 1935, Earnest and John Lawrence, along with the daughter of Marie Curie, discovered artificial radiation and worked to apply it to the treatment of cancer.4 Over the course of many decades, radiation therapy was brought to life. Photon therapy became abundant around the world while proton therapy was hindered and only offered at select places throughout the world: U.S., Sweden, and Europe. Through the 1990’s, many technological advancements were made, such as the CT’s, MRI’s, PET’s, and newer machines. From the 1990’s through the present, six proton therapy treatment facilities have opened and five more are under development as of 2009. The American proton therapy sites are available in the cancer centers of Loma Linda University Medical Center in California, Massachusetts General Hospital, Indiana University, University of Florida, M.D. Anderson in Houston, Texas, and ProCure in Oklahoma City.5 The future of proton therapy has the potential to be a bright one, but experts say that the next decade’s clinical research will largely decide the fate of proton therapy.6
Methods
Proton therapy was once called “the most precise radiation treatment available”, but it is still under investigation and is not used abundantly in clinic yet.4 The force behind proton therapy are the cyclotron or synchrotron, which creates protons, speeds them up, and delivers them to the patient via the linear accelerator, a machine common to all modern cancer centers.7 When the proton enters the patient, it interacts with the cell by pulling the oppositely charged electron out of its orbit, an event called ionization. This ionization manipulates the characteristics of the molecule, and the damaging effects to the nucleus may take place.8 Little healthy tissue is affected, however normal cells have the capability to repair themselves in most cases.
The proton’s distribution is better than photon therapy. Photons start out strongly and release the dose as it travels through tissue, which results in healthy tissue receiving a significant dose of radiation, resulting in unwanted damage and side effects. On the other hand, protons travel in a stable pattern through the tissue, delivering little to no energy until it reaches the end of their path with the Bragg’s peak, an increase in deposited energy. If the plan is calculated and delivered correctly, this Bragg peak will be delivered to the tumor.4 The tumor receives nearly all of the radiation, something that photon therapy cannot achieve. Protons are also much bigger than photons, so they move slower and are able to interact with more electrons, which causes more ionization.8 This results in the tumor getting the most useful portion of the dose while treating less normal tissue giving a better chance of killing the tumor. Since the normal tissue is getting less radiation, the prescribed dose to the tumor can be increased, providing a better chance to eliminate the cancer.7 Along with these benefits, when the healthy tissue is not affected, there are even less side effects involved. These avoided side effects are linked with a better quality of life during and after the battle with cancer. Proton therapy patients are known to continue with their life as it was before cancer by exercising, working , and even vacationing during the duration treatment, something photon therapy and chemotherapy do not generally allow.8
The benefits of proton therapy are similar to those of IMRT: treating the tumor more powerfully, treating less normal tissue, and decreasing side effects. Since proton therapy is an ideal treatment, why not make it the new standard radiation therapy? While it is a new and emerging technology, it is held back by technology, efficacy, insurance, cost, and project planning.9 Just as the first linear accelerators were hard to afford and acquire, so are the proton therapy modalities. After proton therapy proves itself, these complex machines will probably become more abundant and sought-after. Another factor that may push this modality forward is the current implication of 4D proton therapy. This is a process that uses 4D information, treatment planning, and dose calculation, making the treatment more precise.10 It is often associated with intensity-modulated radiation therapy (IMRT).10 Proton therapy is under examination to make it a more feasible and routine procedure.
Proton therapy is presently being used to treat primary cancers of the brain, eye, head and neck, lung, spine, and prostate.7 It is also considered the best choice for pediatric patients because it generously spares the healthy tissue and avoids stunted growths, which is the biggest issue in treating children. Proton therapy works best in cancers that are localized, that is, with no metastases, and it can be paired with other forms of treatment.8 It is also currently under investigation and experimentation for the treatment of breast cancer. The treatment can take anywhere from one day to seven weeks, based on the prescription strength of the dose.8 It is worthy to note that the cure rates in the cancers treated with proton therapy have increased dramatically.4 This explains the desire and urgency to bring proton therapy into modern treatment options.
Discussion
Proton therapy is an up-and-coming technology, but is making ground in the field of oncology. While treatment facilities are hard to access at this point in time, professionals may expect to see more proton therapy centers and machines in the future because steady pros and malleable cons. If more cancer cases can be cured, this pandemic outbreak of cancer can finally be under control and more lives could be saved.
The staff of Mississippi Baptist Health Systems’ Cancer Center of Jackson, Mississippi was asked their opinions about proton therapy. The rulings were quite diverse. The lead radiation therapist was asked first, and he saw a few key problems with the technology. He thought it would be too expensive to take off and that reimbursement for the proton treatments will not be adequate (McNeil S. Oral communication. Mississippi Baptist Health Systems. November 2009). The radiation oncologist seemed to agree. While he did see a few positive aspects of the treatments, such as pediatric malignancies and palliation, he questions the research and efficacy behind the treatments. He also doubted the monetary and political reasoning behind proton therapy, claiming that the money should go to more useful and global causes such as immunizations (Friedman R. Oral communication. MBHS. November 2009). On the flip side of the argument, the men in the physics department seemed to disagree, having a more positive response. A staff dosimetrist stated simply that it will become more common as it becomes more affordable. The Director of the Physics stated that the dose distribution of a proton is pleasing, and he believes that proton therapy is in fact getting cheaper and will continue to rise in radiation therapy departments in the future (Jordan D. Garrett J. Oral communication. MBHS. November 2009.).
While the United States has a handful of proton centers, other countries and areas of the world a completely lacking. An inspiring testimony of proton therapy comes from the Barnes family from the UK. Alex Barnes, a 5 year old boy, was diagnosed with an aggressive brain tumor. The family was given little hope and few treatment options. With the family reaching for the last resorts, they decided to come to Jacksonville, Florida to try the greatly praised proton therapy.5 Alex was under risk for a number of mental and physical disabilities due to the large tumor. After traveling to Jacksonville, Florida from England and undergoing 33 proton therapy treatments, Alex is cured of his tumor with no residing side effects.5 Alex’s results are amazing and miraculous, and is a prime example of the perfect treatments proton therapy can offer. His results would generally not be possible with photon therapy. The entire UK is impressed by this case, and as a result is under discussion and development for their first proton therapy center. Proton therapy is proving itself to be efficient and an untouchable treatment and is beginning to spread around the world.5
While the costs are holding back production, one must remember that all technology is expensive when it is new. Addressing the argument of reimbursement, it has been reported that more insurance companies and even government policies are beginning to cover proton therapy, making it more affordable and therefore more attainable.4 This way, no matter the number of proton therapy candidates, the option would be available, and those qualifying patients would have the best chance of survival. All patients deserve that chance.
Conclusion
As the problem of cancer continues to grow, the field of radiation oncology will also grow. Technology will forever be changing, which means new and emerging modalities. The field is evolving from photon therapy to more modern forms of particle therapy, the most pronounced being proton therapy. Proton therapy offers distinct benefits for treatment, but it does have cons as well. While having a near perfect radiation dose distribution, the efficiency and cost of the treatment are debated. These issues can only be worked out in time. Proton therapy requires much more research and support before it will become widely available, but it has potential to be a great addition to the field of radiation oncology.
References
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