Stricter laws.

It’s thought that the dose constraints for moderately hypofractionated prostate radiation in RTOG 0415 could be more strict. These post-hoc recommendations for tighter dose constraints are important evolutions of treatment technique. That’s because many of the trial constraints were a priori arithmetically derived from conventional constraints. Remember, in the CHHiP trial, men were randomized to 74 Gy in 37 fractions or one of two hypofractionated arms: 60 Gy in 20 fractions or 57 Gy in 19 fractions. Here we have a case-control study from CHHiP exploring the association of anorectal dosimetry and GI toxicity. Qualitatively, intermediate-to-high doses were associated with rectal bleeding while intermediate dose was associated with frequency, pain, and incontinence. Using actual trial toxicity outcomes, they derived much stricter anorectal dose-volume constraints to be used with the CHHiP-style 20 fraction regimen: V20<85%, V30<57%, V40<38%, V50<22%, V60<0.01%. This means that simple conversion of conventional dose constraints to hypofractionated constraints isn’t so simple. TBL: If you use the 20-fraction CHHiP regimen, take note of these newly recommended constraints from an analysis of realized toxicities. | Wilkins, Int J Radiat Oncol Biol Phys 2020