Objective To assess the safety and effectiveness of stereotactic salvage radiotherapy (SSRT) in RT‐naïve patients affected by macroscopic prostate bed recurrence. Patients and methods Consecutive patients treated for prostate bed macroscopic recurrence in three different Italian institutes were reviewed. Patients were treated with SSRT, with a total dose of 30–40 Gy in five fractions, the mean pre‐SSRT PSA level was 2.3 ng/mL. Two different PSA thresholds were defined and biochemical recurrence‐free survival (BCRFS) was reported, in order to better express outcome: BCRFS1 (a PSA level increase of >10% compared to the pre‐SSRT value) and BCRFS2 (a PSA level increase of >0.2 ng/mL for patients with a PSA nadir of <0.2 ng/mL or two consecutive PSA level increases of >25% compared to nadir in patients with a PSA nadir of <0.2 ng/mL). Results In all, 90 patients were treated, with a mean (range) follow‐up of 21.2 (2–64) months, and 17 of these patients (19%) had concomitant androgen‐deprivation therapy (ADT) during SSRT. Complete biochemical response, defined as a PSA nadir of <0.2 ng/mL, was obtained in 39 of the 90 patients (43.3%). Considering BCRFS1, 25 patients (27.8%) had BCR, with an actuarial median BCRFS1 time of 36.4 months. For BCRFS2, BCR was reported in 32 patients (35.5%), with an actuarial median BCRFS2 time of 24.3 months. There was no Grade >2 toxicity. Conclusions SSRT was found to yield significant biochemical control and allowed ADT delay despite adverse features.

CTV coverage analysis provided an a-posteriori evaluation of the treatment geometric accuracy and allowed a quantitative verification of the adequacy of the PTV margins applied in CyberKnife LOT treatments offering guidance in the selection of CTV margins.

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