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To evaluate tolerance and feasibility of an ultra-hypofractionated urethra-sparing SBRT schedule after radical prostatectomy

From April-2019/September-2021, 51p with median age of 68-yo (55-80) were prospectively included. Patients’ characteristics are detailed in table 1. Adjuvant radiotherapy (ART) in 16p (31%) and salvage radiotherapy (SRT) in 35p (69%); median time from surgery to ART 4.5 months (1-9) vs. 17 months (7-213) to SRT.

All patients underwent VMAT 36.25Gy in 5 fractions of 7.25Gy on every-other-day to surgical bed (RTOG guidelines). Urethra-sparing protocol reduced prescribed dose/fraction to urethra and surrounding zone from 7.25Gy to 6.5Gy; 13p (25.5%) underwent elective nodal pelvic irradiation with 26Gy in 5 fractions of 5.2Gy and 5p with macroscopical pelvic nodal disease received simultaneous integrated boost at a dose of 40Gy in 5 fractions of 8 Gy. Thirty-two (63%) were treated in a Novalis-Linac with daily ExacTrac-IGRT based upon prostate-bed gold-fiducial markers, whereas 19p (37%) were treated in a Versa-HD-Linac with Clarity-4D-Monitoring-IGRT-system. Daily immobilizationwith endorectal balloon filled-up with 80cc air to minimize rectal movements was used. All patients received alpha-1-receptor antagonists before, during and up to one month after completing SBRT; 13p (25.5%) received androgenic deprivation therapy (ADT) for a median time of 24 months (range 6-24).

We reported results of biochemical progression-free survival (bPFS) defined according to ARTISTC criteria (PSA ≥0.4 ng/mL and rising after completion postoperative SBRT); clinical progression-free survival (cPFS) defined as no evidence of local or metastatic progression excluding evidence of biochemical recurrence  and distant metastases free-survival (DMFS

After median follow-up 10months (1-27) all patients are alive; 6p (12%) developed biochemical progression at a median time of 12 months (9-22) with 1y and 2y bPFS of 81.6% and 66% respectively; 4p (8%) developed clinical progression (1p local+distant metastases, 1p nodal regional and 2p distant metastases solely) at a median time of 16 months (6-22) with 1y and 2y cPFS of 97.5% and 74.3% respectively; finally, 1y and 2y DMFS were 97.5% and 83.8% respectively (Fig. 1)

Acute toxicity: genitourinary G1 11p (22%), G2 4p (8%); gastrointestinal G1 9p (18%), G2 3p (6%). Late toxicity (follow-up >90 days):gastrointestinal G1 4p (8%), G2 1p (2%); genitourinary G1 5p (10%), G2 1p (2%); gastrointestinal G1 4pm (8%), G2 1p (2%)

Ultra-hypofractionated adjuvant/salvage SBRT seems to be feasible and safe after radical prostatectomy. Longer follow-up is necessary to confirm observed results.