CHHiP off the old margin.

Top Line: The CHHiP trial was the UK’s randomized trial of prostate radiation demonstrating the non-inferiority of 60 Gy in 20 fractions (but not 57 Gy in 19 fractions) compared to 74 Gy in 37 fractions.

The Study: Embedded within the trial was a randomized phase 2 study of image guidance (IGRT) and reduced target margins. You may recall, there have been several studies suggesting that smaller margins and more sophisticated imaging do nothing to reduce toxicity while possibly even increasing the risk of failure. Of the over 3000 patients in CHHiP, 293 were also enrolled in the IGRT sub-study where they were randomized (again) to standard margins with no IGRT, standard margins with daily IGRT, or reduced margins with daily IGRT. Remember, CHHiP used confusing, multiple simultaneous-integrated boost volumes with various margins. To recap, the prostate and seminal vesicles with a 10 mm (5mm posterior) margin received 80% of prescription; the prostate with a 10 mm (5mm posterior) margin received 96% of prescription; and the prostate with a 5 mm (0 mm posterior) margin received 100% of prescription. Wait, they did this without IGRT? Anyway, in the reduced-margin arm, the 10 mm and 5 mm margins above were reduced to 6 mm and 3 mm. Acute grade 2+ toxicity rates were 24-28% for GI and 44-53% for GU. Late grade 2+ toxicity was 2% across the board for GU and 6-8% for GI.

TBL: Though it improved dosimetry, the use of daily IGRT and reduced target margins did not appear to dramatically reduce toxicity during prostate radiation on the CHHiP trial. | Murray, Radiother Oncol 2019