By Martha Kerr, BSN
BOSTON -- September 26, 2008 -- Use of protons instead of conventional photon radiation results in an almost 3-fold reduction in the risk of cancer recurrence in patients with malignancies, researchers reported here at the American Society for Therapeutic Radiology and Oncology (ASTRO) 50th Annual Meeting.
The findings were from an analysis of data from a retrospective cohort study of 503 patients treated with proton therapy from 1974 to 2001 at the Harvard Cyclotron in Cambridge, Massachusetts, with 1,591 patients from the Surveillance, Epidemiology, and End Results cancer registry treated with conventional photon radiation.
Patients in the 2 groups were matched by age at radiation treatment, year of treatment, cancer histology, and site of treatment. The analysis was restricted to patients with 1 or more years of follow-up. The primary endpoint was the risk of a second malignancy in any site after radiation therapy.
Investigator Nancy Tarbell, MD, Pediatric Radiation Oncology Unit, Massachusetts General Hospital, and Department of Radiation Oncology, Harvard Medical School, Boston, Massachusetts, presented the results on September 24.
At treatment, patients in the proton cohort a median of 56 years old and the photon cohort was a median of 59 years old.
Results show that 6.4% of patients treated with proton therapy and 12.8% of those treated with photon radiation developed a second malignancy.
Median duration of follow-up was 7.7 years in the proton cohort and 6.1 years in the photon cohort.
After adjusting for gender and age at treatment, photon therapy was strongly associated with an increased risk of a second malignancy (P < .0001, adjusted hazard ratio = 2.73; 95% confidence interval, 1.87-3.98).
Dr. Tarbell speculated that the reason for the significant reduction in second cancers is because proton radiation is focused more precisely on the target area. A lower dose of radiation is required and less is delivered to surrounding tissues.
The findings contradict the theory that proton radiation might increase rather than decrease the incidence of secondary cancers because of scatter radiation.
"This study could have a substantial impact on the care of patients," Dr. Tarbell said.
"Since cancer patients are surviving for longer periods of time, side effects of therapy are becoming increasingly important for physicians to consider when developing treatment plans," she said.
"Since this is a retrospective study, however, we will need additional studies to further prove this hypothesis," the research team noted.
[Presentation title: Comparative Analysis of Second Malignancy Risk in Patients Treated With Proton Therapy Versus Conventional Photon Therapy. Abstract 17]
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