What urethral dose constraints would you use off-trial for reirradiating the prostate using SBRT? Do you exclude the urethra (or urethra+3mm) from the PTV?  

With the increasing volume of these cases that we are treating outside of clinical trials, it would be useful to learn what urethral constraints are used. The PTV dose ranges from 30 to 36Gy , commonly 34Gy.  I use a combination derived from retrospective series: Urethra +3mm V31.5Gy<50%; V24Gy<30%; V36Gy<1cc. This is close to the  ongoing French trial, GETUG-AGU 31 (NCT03438552)  salvage stereotactic radiation in patients with intraprostatic tumour recurrence after external radiation therapy-study protocol: Urethra +3mm  V24 Gy <30%; Dmax (35mm3 )<39Gy, V36 Gy <1 cc. But quite different to the NIH Protocol #:17-C-0153 NCT03253744, Dose Escalated Prostate SBRT for Locally Recurrent Prostate Cancer after Prior Radiotherapy to doses 40Gy,  42.5Gy, and 45Gy and urethral constraint of < 105% PTV tumor dose i.e. 42Gy, 44.6Gy and 47.25 for the 3 respective dose levels.