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2019 ASCO: Study Finds Proton Therapy Reduces Adverse Events, Results in Similar Survival vs Photon Therapy

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Key Points

  • A total of 45 patients (11.5%) treated with proton therapy experienced a grade 3 or higher side effect. In the photon therapy group, 301 patients (27.6%) experienced a grade 3 or higher side effect.
  • A weighted analysis of both patient groups found that the relative risk of a severe toxicity was two-thirds lower for patients treated with proton therapy vs those treated with photon therapy.
  • Overall survival and disease-free survival were similar between the two groups.

In a trial presented by Baumann et al at the 2019 ASCO Annual Meeting (Abstract 6521), patients with locally advanced cancer treated with proton chemoradiotherapy instead of traditional photon chemoradiotherapy were at a lower risk of experiencing side effects. However, cure rates were almost identical between the two groups.

“We looked at grade 3 side effects, including pain or difficulty swallowing, difficulty breathing, nausea, or diarrhea, among others, [which were] often severe enough for patients to be hospitalized,” said the study’s lead author Brian Baumann, MD, Adjunct Assistant Professor of Radiation Oncology in the Perelman School of Medicine at the University of Pennsylvania and Assistant Professor of Radiation Oncology at Washington University School of Medicine in St. Louis. “Our clinical experience is that [patients treated with] concurrent chemoradiation therapy [and] treated with protons rather than photons tend to have fewer side effects. While there is some literature supporting that finding for several disease sites, we did not expect the magnitude of the benefit to be this large.”

Study Methods

For this study, researchers evaluated data on 1,483 patients, 391 of whom received proton therapy and 1,092 who underwent photon treatment. All patients had nonmetastatic cancer and were undergoing chemotherapy and radiation intended to be curative. Patients with brain cancer, head and neck cancer, lung cancer, gastrointestinal cancer, and gynecologic cancer treated with concurrent chemoradiation were included. The primary endpoint was 90-day adverse events associated with unplanned hospitalizations (Common Terminology Criteria for Adverse Events, version 4.0, grade ≥ 3). 

Findings

Data showed 11.5% (45) of patients treated with proton therapy experienced a grade 3 or higher side effect. In the photon therapy group, 27.6% of patients (301) experienced a grade 3 or higher side effect. 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 patients treated with proton therapy vs patients treated with photon therapy. Overall survival and disease-free survival were similar between the two groups. 

“There are several trials underway, but they are all dealing with a variety of barriers, so it will be years before we have that data. That’s why the information we do have is so critical, and our findings here point to a real benefit for our patients,” said senior study author James Metz, MD, Chair of Radiation Oncology, leader of the Roberts Proton Therapy Center at the University of Pennsylvania, and a member of the Abramson Cancer Center.

Disclosure: For full disclosures of the study authors, visit coi.asco.org

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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