Proton therapy may decrease risk for secondary cancers

ASTRO 50th Annual Meeting

The results of a 26-year retrospective study suggest that patients who received proton radiation therapy may cut the risk for secondary malignancies by more than 50% compared with patients treated with standard photon radiation.

Nancy Tarbell, MD, C.C. Wang professor of radiation oncology and dean of academic and clinical affairs at Harvard Medical School, presented the results at the American Society for Therapeutic Radiology and Oncology’s 50th Annual Meeting in Boston.

Researchers at Harvard and Massachusetts General Hospital examined the records of 1,450 patients treated with proton radiation at the Harvard Cyclotron between 1974 and 2001, and compared 503 of those patients with 1,591 patients in the SEER registry who were treated with photons therapy.

The researchers found that 6.4% of the patients treated with protons developed secondary cancers compared with 13.1% of the patients who received photon radiation.

“It’s one more reason to justify protons,” Tarbell told HemOnc Today. “We didn’t expect it to be this significant.”

Tarbell said patients in the study primarily had brain, head and neck cancers, epithelial tumors, sarcomas and prostate cancers. Median follow-up in the proton group was 7.7 years and 6.1 years in the photon group.

After adjusting for gender and age at treatment, the researchers concluded that photon radiation therapy was strongly associated with an increased risk for secondary cancers (HR=2.73; P<.0001).

“In the pediatric cohort, we’re very interested,” Tarbell said. “If this finding is true in adults, it has to be even more important for young patients where second malignant tumors are such a big issue.” – by Jason Harris

This is a helpful but still inconclusive study. It looked at patients treated at Massachusetts General Hospital with protons in the 1990s who had sufficient follow up. The researchers looked for second cancers in those patients by reviewing their charts, and then compared them with matched patients from a national database. They were, to some degree, comparing apples to oranges as it is possible that one method may capture the incidence of second cancers better than another. Though this study does not prove that protons reduce the risk of second cancers there had been a fear that protons could even increase that risk by generating particles called neutrons. I think we can now say that proton therapy doesn’t do this but it’s going to take more definitive studies and longer follow-up.

– Anthony L. Zietman, MD

Professor of Radiation Oncology at Harvard Medical School

For more information:

Chung CS, Keating N, Yock T, Tarbell N. Comparative analysis of second malignancy risk in patients treated with proton therapy vs. conventional photon therapy. Presented at: the American Society for Therapeutic Radiology and Oncology’s 50th Annual Meeting; Sept. 21-25, 2008; Boston.