Are Protons Better Than Photons for Prostate Radiation Treatment?

English: Depth dose of electrons, x rays or pr...
English: Depth dose of electrons, x rays or protons entering human tissue for the purpose of cancer treatment (Photo credit: Wikipedia)

Massachusetts General Hospital, University of Pennsylvania (USA), and several other proton centers are participating in a clinical trial that may help to settle a long-running debate: Is proton beam therapy (PBT) ore effective and safe than intensity-modulated radiation therapy (IMRT) for prostate cancer?

The Trial: Prostate Advanced Radiation Technologies Investigating Quality of Life (PARTIQoL) is the first large Phase III randomized clinical trial to directly compare PBT against IMRT. It is a 5 year trial that opened in July 2012, and is still accruing patients.

The Modalities: PBT and IMRT are advanced technologies capable of delivering higher doses of radiation more directly to the prostate, as compared to older technologies. These higher doses can lead to higher cancer control rates. By reducing the dose to surrounding normal structures (such as the bladder, rectum, and small intestines), side effects may be reduced as well. Unlike IMRT, Proton Beam Therapy delivers radiation using a more focused beam to the target, with less of a low-dose bath in the pelvis and (theoretically) no exit dose beyond the tumor. In theory, PBT may cause fewer side effects than does IMRT.

What Do We Know Now? The few studies comparing protons with IMRT are few in number, and have been retrospective (or backward looking, potentially introducing significant bias). A 2012 study in the Journal of the American Medical Association (JAMA) found that patients treated with PBT had improved unitary function in the short-term. But the study is flawed: It relied on physician billing codes, rather than patient reports. Earlier this year, Dr. Efstathiou and colleagues described patient-reported outcomes following PBT, IMRT, or 3-D conformal radiation therapy. PBT caused fewer gastrointestinal side effects and urinary problems, but by 2 years, outcomes were similar to IMRT.

Costs? According to the 2012 JNCI study, median Medicare reimbursement for PBT is $32.428, compared with $18,575 for IMRT.

My Take: Proton Beam Therapy has an established role for pediatric malignancies (and uveal melanomas). Hopefully, we will learn whether it has an advantage over IMRT with this important clinical trial. For now, either IMRT or PBT are appropriate radiotherapeutic approaches for localized prostate cancer. You may be a candidate for surgery, active surveillance, or radioactive seed implant, depending on your cancer risk, medical condition, age, life expectancy, and personal preferences. I’m Dr. Michael Hunter.

The small print: The material presented herein is informational only, and is not designed to provide specific guidance for an individual. Please check with a valued health care provider with any questions or concerns. As for me, I am a Harvard- , Yale- and UPenn-educated radiation oncologist, and I practice in the Seattle, WA (USA) area. I feel genuinely privileged to be able to share with you. If you enjoyed today’s offering, please consider clicking the follow button at the bottom of this page.

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References: http://clinicaltrials.gov/ct2/show/NCT01617161; Efstathiou JA et al. British Journal of Cancer 108 (6) 1225-1230; Sheets NC et al. JAMA 2012; 307(15):1611-1620; Journal of the National Cancer Institute 2013 Jan 2; 105(1):25-32.

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