S. Arcangeli1, C. Chissotti1, F. Ferrario1, R. Lucchini1, M. Belmonte1, G. Purrello1, R. R. Colciago1, E. De Ponti2, V. Faccenda2, and D. Panizza2; 1University of Milan Bicocca - School of Medicine and Surgery, Milan, Italy, 2Fondazione IRCCS San Gerardo dei Tintori - Medical Physics Department, Monza, Italy
Purpose/Objective(s): To assess the incidence of both acute and late gastrointestinal (GI) and genitourinary (GU) side effects in patients with organ-confined unfavorable prostate cancer (PCa) treated with single-dose ablative radiotherapy (SDART). Materials/
Methods: Thirty patients enrolled in a single-arm prospective trial (NCT04831983) received 24 Gy SDART to the whole prostate with urethra-sparing and organ motion control. The treatment was delivered on a Linac platform using a 10MV FFF single partial arc. ADT was prescribed as per standard of care. Treatment-related GU and GI toxicities (CTCAE_v5 scale) and QoL outcomes (EORTC QLQ-PR25/C30, IPSS, IIEF 5) were assessed at different time points. Minimal Important Difference (MID) was established as a change of >0.5 pooled SD from baseline. The significance of the differences between QoL outcomes at baseline, 3-month, and last follow-up was tested through the analysis of variances. A logistic regression univariate and multivariate (MVA) analysis was performed to evaluate potential associations between specific patient-related, tumor-related, or treatment-related factors and clinical outcomes. Results: All patients completed the treatment according to the protocol’s schedule. The median follow-up was 18 months (range, 6-31), with no =G3 side effects observed. Within 3 months post-treatment, there was only one instance of G1 acute GI toxicity, while 2 patients had G2 acute urinary toxicity. G2 late GI and G2 late GU toxicities occurred in 1 and 2 patients, respectively. Late GI toxicity of any grade correlated with maximum rectal dose (P=0.021), while lower baseline QoL score (P=0.025), higher baseline IPSS score (P=0.049), acute GU toxicity (P=0.029), and acute urinary domain MID (P=0.045) predicted late GU toxicity of any grade. In MVA, only baseline QoL score (OR 0.95, P=0.031) and acute GU toxicity (OR 8.4, P=0.041) remained significant. Significant QoL change was observed only in the urinary domain (P=0.005), with a median increase from 8 to 17 in the questionnaire score. Late urinary MID correlated with acute urinary MID (P=0.003), acute QoL MID (P=0.029), acute GU toxicity (p=0.030), and lower baseline urinary score (P=0.033). In MVA, only acute urinary MID predicted late urinary MID (OR 9.7, P=0.035). All patients were found biochemically controlled at the time of analysis, with median PSA level decreased from 8.05 ng/ml (range, 3.41 – 18.27) at baseline to 0.10 ng/ml (range, 0.01 – 1.46) at the last follow-up. Conclusion: Our findings provide promising data on the feasibility and safety of 24 Gy SDART of the whole prostate with urethra-sparing and organ motion control associated with ADT in organ-confined unfavorable PCa. Long-term follow-up is needed to confirm these results.
