Session Item

While prostate cancer treatment is increasingly effective its toxicities remain a great concern. In this study, we report on the adverse events (AE) of post-prostatectomy irradiation based on our institutional experience, review the reproducibility of organs-at-risk (OAR) contouring, and finally investigate the association of various dose-volume parameters with treatment sequelae.

We included 167 consecutive patients who had received post-prostatectomy radiotherapy (either adjuvant or salvage) to the prostatic bed with or without pelvic node irradiation. The medical history was reviewed for AE, which were scored according to the CTCAE v.5.0 AE reporting guidelines. The rectum and bladder organs-at-risk were contoured anew, based on the treatment planning computed tomography, following RTOG/NRG Guidelines. The volumes were then compared with the original contours and analyzed based on dose-volume histogram (DVH) values using ROC curves. Kaplan-Meier curves were used to estimate the cumulative rate of toxicity at given time-points (3 months and 5 years).

The median patients’ age was 63.2 (IQR 58.8 – 67.5), and the median follow-up was 51 months (IQR 22.4-97.1). Grade 2 or higher urinary tract toxicity occurred in 13.3% and 28.2% of the patients at 3 months and 5-years, respectively. A total of 17 (10.2%) patients experienced grade 3 or higher toxicity within the follow-up, most commonly (8.4%) associated with urinary tract obstruction requiring surgical intervention. Grade 2 or higher rectal toxicity occurred in 7.2% and 13.9% of the patients at 3 months and at 5 years. Grade 3 or higher rectal toxicity was much less frequent; reported in 2.4% of patients.

There was a trend towards a lower volume of the new rectal contours, as compared to the originally delineated organ, which was found in a majority of the patients (74.9%). The new contours were smaller by a median of 16.5% (IQR 8-28.5). The bladder contours were comparable in approximately 50.9% of patients, and in the majority (83.5%) of the remaining patients, the difference compared to the initial OAR volume was low (<10%).

Table 1 presents the association between consecutive dose-volume parameters and grade II or higher rectal and urinary AEs. The presented values, however, did not reach statistical significance.

Table 1. AUC values in ROC analysis of selected DVH parameters for the occurrence of grade II or higher GI or GU toxicity. Vx represents the volume (%) of OAR receiving a dose of at least x Gy.

Our analysis suggests that the rectal contours might often be overestimated, which can result in a bias towards accepting higher doses to the rectum when assessing dose-volume parameters. Moreover, the overall treatment toxicity of post-prostatectomy radiotherapy seems to be not neglectable, especially in terms of significant urinary tract adverse events such as urinary tract obstruction.