CHIRP.

Top Line: Is there a difference in toxicity when treating the prostate and elective nodes with a conventional, sequential boost technique or a moderately hypofractionated, simultaneous integrated boost technique?

The Study: Recently, the POP-RT trial showed that the addition of elective pelvic nodal RT (50 Gy in 25 fractions) to moderately hypofractionated prostate RT (68 Gy in 25 fractions) improved 5-year biochemical failure-free survival and disease-free survival in men with (mostly) high risk prostate cancer. While moderately hypofractionated (HF) regimens lend themselves nicely to simultaneous elective nodal treatment, it’s unclear if this technique increases toxicity compared to sequential, conventional fractionation (CF). The single center, phase 2 CHIRP trial sought to compare late GI toxicity between conventional and moderately hypofractionated RT to the prostate and pelvic nodes. Over 100 patients with high risk disease being treated with RT and 18 months of ADT were randomized to CF or HF. The CF arm consisted of 46 Gy in 23 fractions to the pelvis followed by a cone-down boost to a total of 78 Gy in 39 fractions to prostate +/- SVs). The HF arm delivered 45 Gy to pelvic nodes and 68 Gy to the prostate +/- SVs in the same 25 fractions. There was no significant difference in the rate of acute grade 2+ GI toxicity (19% HF, 22% CF) or GU toxicity (30% HF, 31% CF). There was also no significant difference in the rate of late grade 2+ GI toxicity (16% HF, 10% CF) or GU toxicity (16% HF, 6% CF). In POP-RT, adding pelvic RT increased late GU toxicity (20% vs 9%) but not GI toxicity (8% vs 5%).

TBL: In this phase 2 trial, using a moderately hypofractionated, SIB technique to treat the prostate and pelvic nodes did not increase acute and late toxicity rates compared to conventional fractionation. | Wang, Pract Radiat Oncol 2021