"This is exciting because it shows that proton therapy offers a way for us to reduce the serious side effects of chemo-radiation and improve patient health and wellbeing without sacrificing the effectiveness of the therapy," said the study's lead author Brian Baumann, MD, an adjunct assistant professor of Radiation Oncology at Penn and an assistant professor of Radiation Oncology at Washington University School of Medicine in St. Louis.
Proton therapy has a few key differences from traditional photon radiation. Photon radiation typically uses multiple x-ray beams to deliver radiation to the tumor target but unavoidably deposits radiation in the normal tissues beyond the target, potentially damaging those tissues as the beam exits the body. Proton therapy is an FDA-approved alternative radiation treatment that directs positively charged protons at the tumor. They deposit the bulk of the radiation dose to the target with almost no residual radiation delivered beyond the target, reducing damage to surrounding healthy tissue and potentially reducing side effects.
For this study, researchers evaluated side effects including pain or difficulty swallowing, difficulty breathing, nausea, or diarrhea, among others. Researchers focused on grade-three effects or higher, defined as side effects severe enough for patients to be hospitalized. They evaluated data on 1,483 cancer patients receiving radiation and chemotherapy at the same time. Of these, 391 patients received proton therapy, while 1,092 underwent photon treatment. All patients had non-metastatic cancer and were undergoing treatment intended to be curative. Patients with brain cancer, head and neck cancer, lung cancer, gastrointestinal cancer, and gynecologic cancer treated with concurrent chemo-radiation were included.
The primary outcome was whether or not patients experienced adverse side effects that were grade-three or higher within 90 days of treatment. In the proton group, only 11.5 percent of patients (45) did, compared to 27.6 percent of patients (301) in the photon group. A weighted analysis of both patient groups, which controlled for other factors that may have led to differences between the patient groups, found that the relative risk of a severe toxicity was two-thirds lower for proton patients compared to photon patients.