Daily IGRT in Prostate Cancer Reduces Risk of Recurrence, Increases Risk of Second Cancer

During a session at the 2018 Genitourinary Cancers Symposium, study results showed that daily image-guided radiotherapy (IGRT), when compared to weekly control, decreases the risk of recurrence and rectal toxicity, but is associated with an increased risk of second cancer.

“While there is a strong rational for prostate cancer IGRT, optimal frequency of the control is not clearly identified,” said Renaud de Crevoisier, MD, PhD, professor, University of Rennes, radiation-oncologist, Regional Cancer Center. “It may be possible to correct only for the systematic error by doing a control on day 1, 2, 3, and weekly, or it may be necessary to correct for systematic and random error by doing a daily control.”

The phase 3 randomized trial comprised of 2 steps: the first was a feasibility step for the first 5 patients. Then, 470 patients from 21 centers were randomized 1:1 between 2 arms: weekly control or daily control between June 2007 and November 2012.

According to Crevoisier, the hypothesis was to detect a minimum of a 12% difference in 5-year disease-free survival (DFS) between the groups. The patients were stratified between center, prognostic group, total dose, and androgen deprivation therapy. The median follow-up was 4.1 years. Secondary outcomes included overall survival (OS) and toxicity. Post-hoc analyses included biochemical progression-free interval, clinical progression-free interval and second cancer-free interval.

For toxicity, acute rectal bleeding greater than grade 1 decreased significantly in the daily control group (6% versus 11%). Rectal toxicity, BPFI, and clinical recurrence also decreased significantly in the daily control group.

Surprisingly, OS decreased in the daily control group, said Crevoisier. The risk of death increasedby a factor of 2. Looking at second cancer incidence in the post-hoc analysis, the risk of second incidence was also multiplied by 2 in the daily control group.

“Compared to weekly control, by improving targeting, daily control in prostate cancer IGRT significantly decreases the risks of recurrence and rectal toxicity but is associated with an increased risk of second cancer,” concluded Crevoisier. “Longer follow-up is however clearly needed to assess the rate of radiation-associated malignancies.”