Proton therapy maintains efficacy, reduces toxicity of radiotherapy for locally advanced cancer
CHICAGO — Proton chemoradiotherapy significantly reduced incidence of adverse events associated with unplanned hospitalizations compared with traditional photon chemoradiotherapy among adults with nonmetastatic cancers, according to results of a comparative effectiveness study presented at ASCO Annual Meeting.
Results also showed similar survival outcomes regardless of whether patients underwent proton or photon radiotherapy.
“In almost every case, proton therapy is able to deliver a lower dose to the normal tissues adjacent to the targeted tumor than conventional radiation,” Brian C. Baumann, MD, radiation oncologist at Washington University School of Medicine in St. Louis, told HemOnc Today. “We hypothesized that this dose reduction would be associated with a lower risk for complications. Protons were just as effective at preventing disease recurrence, so the reduction in toxicity did not come at the expense of reduced effectiveness.”
Concurrent chemotherapy and radiotherapy is standard-of-care curative treatment for a variety of cancers, but it can lead to substantial morbidity among patients.
Photon radiation uses multiple X-ray beams directed against a tumor, but can damage normal, healthy tissue as the beam exits the body. Conversely, proton therapy directs positively charged protons at the tumor, within minimal residual radiation to surrounding tissue.
Baumann and colleagues compared 1,483 adults with nonmetastatic cancer treated with curative-intent proton chemoradiotherapy (n = 391; median age, 66 years) vs. photon chemoradiotherapy (n = 1,092; median age, 61 years) from 2011 to 2016 at University of Pennsylvania for brain tumors, head and neck cancer, lung cancer, gastrointestinal cancer and gynecologic cancer.
“We investigated this question because we wanted to see if proton therapy could be just as effective as photon therapy but with reduced side effects,” Baumann said.
Not only were patients treated with proton therapy significantly older, but they had less favorable Charlson-Deyo comorbidity scores (median, 3 vs. 2) and lower integral radiation dose to tissues outside the target (P < .05 for all). However, the groups had similar baseline toxicity and performance status.
Ninety-day grade 3 or worse adverse events associated with unplanned hospitalizations served as the study’s primary endpoint. Secondary endpoints included decline in ECOG performance status during treatment, 90-day grade 2 or worse adverse events, DFS and OS.
Overall, 11.5% (95% CI, 8.3-14.7) of patients treated with proton therapy experienced a grade 3 or worse adverse event, compared with 27.6% (95% CI, 24.9-30.2) of the photon therapy group. Thus, patients treated with proton therapy were 69% less likely to experience a grade 3 adverse event by day 90 (RR = 0.31; 95% CI, 0.15-0.66).
Patients treated with proton therapy also were less likely to experience a grade 2 or worse adverse event by 90 days (RR = 0.78; 95% CI, 0.65-0.93) and a decline in performance status during treatment (RR = 0.51; 95% CI, 0.37-71).
DFS and OS appeared comparable between the groups.
“I think these results have the potential to change clinical practice,” Baumann told HemOnc Today. “More research is needed, particularly prospective clinical trials of proton vs. photon chemoradiation therapy, to confirm these findings.”
There are several other questions that additional research should explore, he added.
“By reducing side effects, proton therapy offers opportunities to further escalate therapy, either with higher radiation dose or more intensified chemotherapy,” he said. “It also offers opportunities for treating older, sicker patients with definitive chemoradiation therapy.” — by Alexandra Todak
Baumann BC, et al. Abstract 6521. Presented at: ASCO Annual Meeting; May 31-June 4, 2019; Chicago.
Disclosures: Baumann reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.