Session Item

To report oncological outcomes and toxicities of a series of clinically localized prostate cancer (PCa) patients treated with SBRT using two RT schedules.

We analysed a prospective database on clinically localized PCa patients treated with SBRT consisting of 42 Gy/7 fx or 36,25 Gy/5 fx on alternate days from January 2013 and September 2020. The inclusion criteria were histologically verified adenocarcinoma, cT1c-T3bN0M0, WHO PS 0-2. No patients received any ADT. SBRT was delivered with volumetric-modulated arc therapy (V-MAT). Daily cone beam CT and fiducial markers image-guidance was used. Biochemical recurrence was defined according to Phoenix criteria (nadir +2 ng/mL). Survival analysis was performed using the Kaplan-Meier method and the log rank test was applied to compare the effect of the individual variables (age, ISUP, initial PSA, TNM, NCCN risk classification) on different outcomes. Patients treated with 7 fx and 5fx were matched via propensity score. The following variables were included in the model: age, PSA at diagnosis, ISUP and clinical tumor stage. Acute and late genitourinary (GU) and gastrointestinal (GI) toxicities were graded using the Common Terminology Criteria for Adverse Events,version 5.0.

Median follow-up was 50 months (IQR, 30,3-69,6). Twenty-five (16%), 48 (30,8%), 43 (27,6%), 31 (19,8%) 8 (5,1%) and 1 (0,7%) patient were classified as very low-risk (VLR), low-risk (LR), favourable-intermediate-risk (FIR), unfavourable-intermediate-risk (UIR), high-risk (HR) and very high-risk group according to the NCCN risk classification. After PS matching 130 patients were identified (65 cases treated with 7 fx and 65 with 5 fx). The 5-year OS was 97,4%. Eight (13.5,1%) patients developed biochemical recurrence after a median time of 34 months (range 15–94). Median bPFS was not reached. 5- year bPFS was 97,3%. RT schedule did not influence bPFS before and after PS matching (p 0.34 and p 0.20). Median MFS was not reached. 5- year MFS was 98,6%. RT schedules were not related to LC and MFS before PS (p 0,97 and 0,66) and after (p 0,99 and 0,16). Age, PSA pre-RT, ISUP, T stage and NCCN risk group did not influence OS, CSS, bPFS, LC and MFS before and after PS matching. No acute nor late G ≥3 toxicities were reported. Forty-one (26,3%) and 45 (28,8%) patients had G1 and G2 acute GU toxicity. Eleven (7%) and two (1,3%) patients had G1 and G2 acute rectal toxicity. PTV>95cc (p 0,036, OR 2,25, 95% CI 1,05-4,81), PTV Dmedian%> 103,3% (p 0,006, OR 2,71, 95% CI 1,33-5,52), bladder D1ccEQD2>75,5 Gy (p 0,032, OR 1,07, 95% CI 1,10-1,14) were related to G2 GU acute toxicities. Multivariate analysis confirmed PTVcc >95cc (p 0,045, OR 2,25, 95% CI 1,02-4,98) and PTV Dmedian > 103,3% (p 0,02, OR 2,47, 95% CI 1,15-5,23). SBRT schedule was not related to G2 acute GU toxicity (p 0,161).

SBRT delivered in 5-7 fx represents an effective and safe treatment for clinically localized PCa. No significant difference between 5 and 7 fx was observed.