What bowel dose constraints do you use when treating bladder cancer with moderate hypofractionation?

Two additional steps I take when using hypofractionation doses as noted above is to 1) ensure that the V55 Gy to small bowel is limited to less than 5 cc (based on some data in gynecological cancers) and 2) make sure the full thickness bowel loop is not in the PTV2 volume.

Good question. In the BC2001 trial reduced high-dose volume (RHDV) arm, PTV1 was outer bladder wall + 1.5 cm and PTV2 was the bladder tumor + 1.5 cm. Oncologic results were similar with RHDV treatment compared to whole bladder irradiation. The hypofractionation option prescription for PTV2 was 55 Gy in 20 fractions of 2.75 Gy. PTV1 dose was 80% of the PTV2 dose (minimum 75%) = 41.25-44 Gy in 20 fractions of 2.06-2.2 Gy to the whole bladder if using concomitant boost hypofractionated technique.

Presumably, most of the bowel dose will be from the larger PTV1 with smaller contribution from PTV2. The 2 Gy equivalent dose for the hypofractionated PTV1 prescription at 75-80% is 41.4-44.7 Gy (aB=10) to 41.4-45.8 Gy (aB=3), which is tolerable. In th...