Proton therapy, or proton beam therapy (PBT), is a type of radiation therapy used to treat prostate cancer or to alleviate its symptoms. Proton therapy is a type of external beam radiation therapy (also called EBRT or EBT) which involves destroying tumors or cancer cells using targeted beams of high-energy particles. Conventional methods of EBRT involve the use of X-rays, whereas proton therapy utilizes protons. Protons are small, positively charged particles that are found in the nucleus of an atom. Beams of protons can be created and energized using large, expensive machines called cyclotrons or synchrotrons. These beams, and the protons within them, can be targeted at the body and into a tumor where they will give off radiation to hopefully destroy the tumor.1,2
The benefits of proton therapy
Unlike radiation that uses X-rays, protons eventually stop within the body. This means, that while X-rays travel through the entire body while they are being targeted at a tumor, protons will settle within the body when their momentum is slowed to a halt as they pass through the skin, muscles, and other organs. Using detailed and specific calculations, the protons can be energized in just the right amount to cause them to come to a halt at a precise location within the body. Once they settle at this location, they will continue to give off their radiation, potentially destroying tumor cells. Conversely, X-rays will give off radiation throughout their entire journey into, and out of, the body.
Treatment with radiation from X-rays may cause more damage to the organs and tissues around the targeted tumor than treatment with proton therapy, since proton therapy doesn’t travel through the entire body at the site of radiation. Being able to spare critical structures from radiation may help reduce treatment-related side-effects, such as bowel or bladder dysfunction. Additionally, the more targeted nature of proton therapy may allow for higher doses of radiation to be given at a time, thus, decreasing overall treatment times. Further, using the newest method of proton beam delivery, called pencil beam scanning, protons can be delivered to the correct location within the body with high-level accuracy.1-4
The drawbacks of proton therapy
Proton therapy is more expensive than traditional radiation therapies as the machinery required to perform proton therapy is costly. It may cost hundreds of millions of dollars to build a facility capable of performing proton therapy, and there are currently fewer than 30 sites across the United States that are capable of performing this treatment option. Additionally, since proton therapy is a relatively new treatment option, and its efficacy is not well known, many insurance companies do not cover it at this time.1,4
What does the research say?
Research into proton therapy for prostate cancer is limited, especially research that directly compares proton therapy to the leading kinds of EBRT, such as intensity modulated radiation therapy (IMRT) which uses varying intensities of X-rays to target tumors. The research that does exist on proton therapy suggests that it may provide a similar benefit post-treatment as IMRT, but with a higher price tag. Additionally, some research indicates that although proton therapy may decrease the risk of developing bowel or bladder-related complications post-treatment, it may lead to a higher risk in developing gastrointestinal-related complications when compared to other forms of EBRT. It’s important to note, however, that these findings are only based on a small number of studies, and more research is needed to determine the efficacy of proton therapy as well as its potential benefits over other radiation therapies.1,4,5
Wisenbaugh ES, Andrews PE, et al. Proton beam therapy for localized prostate cancer 101: Basics, controversies, and facts. Reviews in Urology. 2014; 16(2), 67-75. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4080851/. Accessed July 2, 2018.
Proton Beam Therapy Program: About Proton Therapy. Mayo Clinic. https://www.mayoclinic.org/departments-centers/proton-beam-therapy-program/sections/about-proton-beam-therapy/gnc-20186184. Published November 22, 2017. Accessed July 2, 2018.
Prostate Cancer. Loma Linda University Cancer Center. https://protons.com/proton-treatments/prostate-cancer. Accessed July 2, 2018.
Does Proton Beam Therapy for Prostate Cancer Live Up to its Promise. https://www.healthandwellnessalerts.berkeley.edu/alerts/prostate_disorders/Does-Proton-Beam-Therapy-for-Prostate-Cancer-Live-Up-to-Its-Promise_7833-1.html. Published November 15, 2017. Accessed July 2, 2018.
Odei BCL, Boothe D, et al. A 20-year analysis of clinical trials involving proton beam therapy. International Journal of Particle Therapy. 2016; 3(3), 398-406. Available from: http://theijpt.org/doi/pdf/10.14338/IJPT-D-16-00030.1?code=ptcg-site. Accessed July 2, 2018.