“Proton therapy may very well offer reduced late toxicities. Reflecting back on past reirradiation studies both within and outside of the cooperative groups, it seems that the late toxicities in this retrospective study were somewhat similar,” said David Raben, MD, Professor of Radiation Oncology at the University of Colorado Cancer Center in Aurora, Colorado.

David Raben, MD

“In regard to response and outcomes, one needs to take into account the intervals between the initial treatment and subsequent reirradiation—in this study, the median interval was ~34 months, and we know patients at least 2 years out from initial treatment do better. In addition, the results can be skewed based on how many patients entered into single-institution studies are in fact HPV [human papillomarvirus]-positive vs HPV-negative, as we know the former group typically does better in the recurrent setting,” he noted.

“Past RTOG trials incorporated older radiation techniques, and it would be interesting to compare stereotactic body radioablation using photons vs protons to get a better sense of whether protons truly provide improved response and reduced late toxicity,” Dr. Raben added. “Potentially more exciting would be to utilize very sophisticated radiation delivery models to enhance response to targeted drugs and immunotherapy agents such as checkpoint inhibitors to improve outcomes and maybe change our overall view of how we use radiation therapy.” ■

Disclosure: Dr. Raben is on sabbatical and consulting for AstraZeneca.