Beyond the verge.

Top Line: Are long-term outcomes for anal cancer treated with IMRT comparable to conventional techniques.

The Study: At this point, we sure hope so. RTOG 0529 established dose-painted IMRT (DP-IMRT) as a standard technique when treating anal cancer by reducing acute GI and skin toxicity compared to the historical control of the 5FU/MMC arm of RTOG 9811. But while the IMRT technique improved acute toxicity, some want to see long-term outcomes to be sure it’s just as good as conventional techniques. As a reminder, the 0529 DP-IMRT technique delivered up to 3 simultaneous target doses ranging from 1.5-1.8 Gy per fraction over 28-30 fractions. There were two main long-term questions regarding the use of IMRT for anal cancer: 1) would IMRT result in more marginal misses and higher locoregional failure and 2) would the 1.5 Gy per fraction elective nodal dose adequately control microscopic disease? At 5-years and 8-years the cumulative rate of LRF was 16% and 16% compared to 20% and 22% in 9811. In addition, most of those LRF events (5 out of 8) were persistent disease at 12 weeks after treatment. Three of those 5 with persistent disease were felt to be marginal failures as one involved node and two primary tumors weren’t adequately covered by the high dose PTV. Male gender and nodal involvement were associated with a higher risk of LRF. There were no isolated nodal failures within the elective nodal volumes. Disease-free and overall survival at 8 years were 62% and 68%, respectively (57% and 69% in 9811). Late grade 2 and grade 3 GI/GU toxicity were 29.4% and 5.9%, respectively.

TBL: IMRT for anal cancer reduces acute toxicity while maintaining locoregional control and survival outcomes comparable to conventional treatment techniques. | Kachnic, Int J Radiat Oncol Biol Phys 2021