3324 - Postoperative Hypofractionated Radiotherapy for Prostate Cancer: Late Toxicity and Clinical Outcomes

Purpose/Objective(s): Postoperative radiotherapy (RT) is recommended for patients with PSA recurrence as salvage RT and patients with high-risk pathologic features as adjuvant RT. Due to the low a/ß ratio of prostate cancer (PC), hypofractionated RT (HFRT) has the potential to realize the dose escalation without increasing treatment duration and toxicity. However, current data on postoperative HFRT have been limited, with the majority of studies constrained by short-term follow-up periods. Late genitourinary (GU) toxicities are the primary safety concern, and few investigations have systematically characterized the incidence and related factors of these late GU toxicities. The aim of this study is to evaluate the clinical outcome, late toxicity of a large retrospective cohort with a relatively long follow-up period, and we also identify the factors affecting late GU toxicities.

Materials/Methods: We conducted a retrospective analysis of all PC patients who received postoperative HFRT from 2017 to 2020 at our institution. The inclusion criteria were as follows: (1) RP and histologically confirmed PC; (2) the dose of prostatic bed CTV was 62.75 Gy in 25 fractions; (3) no distant metastases before RT. Daily image-guided intensity modulated RT was performed in all patients. Acute and late GU and gastrointestinal (GI) toxicity were graded using CTCAE, v5.0. Endpoints of the analysis were outcome in terms of overall survival (OS), disease specific survival (DSS), biochemical progression free survival (bPFS) and event free survival (EFS). Univariate and multivariate Cox regression analyses were performed to test the association.

Results: A total of 326 patients were included in the analysis. The median age was 66 years (range: 48-84) and median follow-up was 51 months (range: 13-76). At baseline, patients with =pT3a, positive margin, Gleason score 8-10 and PSA_max =20 ng/mL took 73.3%, 61.0%, 51.8% and 38.6%, respectively. The 5-year OS, DSS, bPFS and EFS rate were 94.6%, 98.5%, 90.7% and 74.7%, respectively. 6.1% and 2.5% patients reported acute G2 GI and G2 GU toxicity. 1.5%, 28.8% and 9.2% patients reported late G2 GI, G2 GU and G3 GU toxicity. The most frequent late =G2 GU events were incontinence worsening and hematuria. Univariate analysis identified bladder V60Gy (%) as a predictor of late =G2 hematuria. For late =G2 incontinence worsening, univariate analysis revealed three associations: preRT G2-3 incontinence, bladder V60Gy (%), and bladder V50Gy (%). Multivariate analysis confirmed preRT G2-3 incontinence as an independent predictor of late =G2 incontinence worsening. Patients receiving cystoscopy exhibited a significant higher rate of =G2 incontinence worsening than did those who did not undergo (p<0.001).

Conclusion: The clinical control in this HFRT series appears promising, and longer follow-up may be needed to collect more late toxicity data, especially GU toxicity. Limiting bladder V60 Gy may reduce RT-related hematuria. The benefit and risk should be balanced when performing cystoscopy.