ESTRO 2021 Abstract Book

S1110

ESTRO 2021

There was a significant improvement in rectal dosimetry in patients with SpOAR across both groups, with a trend towards improved urethral dosimetry in the SpOAR group. SpOAR was not found to adversely affect prostate coverage, and in the trimodal group was found to significantly improve it. (Table 2).

Conclusion Use of rectal spacing gels in patients treated with LDR-PB results in a significant increase in mean distance between prostate and anterior rectal wall. As a result, there is a significant reduction in rectal dose, whilst not compromising the prostate coverage. Longer-term follow-up is currently underway to correlate this with improved quality of life outcomes. PO-1353 Postoperative hypofractionated RT for prostate adenocarcinoma: results from a large series L. Nicosia 1 , C. Vitale 2 , F. Cuccia 2 , V. Figlia 2 , N. Giaj-Levra 2 , R. Mazzola 2 , F. Ricchetti 2 , M. Rigo 2 , R. Ruggieri 2 , S. Cavalleri 3 , F. Alongi 2,4 1 IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Advanced Radiation Oncology, Negrar, Italy; 2 IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Advanced Radiation Oncology Department, Negrar, Italy; 3 IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Urology Division, Negrar, Italy; 4 University of Brescia, Brescia, Negrar, Italy Purpose or Objective conventionally fractionated postoperative radiotherapy demonstrated to reduce biochemical relapse in prostate adenocarcinoma (PCa), and early-salvage RT (esRT) demonstrated similar oncological results as compared with adjuvant RT (aRT), but with a safer toxicity profile. Given the PCa low α/β ratio would be of interest to evaluate the role of hypofractionation also in the postoperative setting. Materials and Methods the mono-institutional data of 304 PCa patients were retrospectively analyzed. 105 patients underwent aRT, 77 esRT, and 122 salvage RT (sRT). Mild-hypofractionated treatment dose in 30 fractions were 66 Gy in the aRT group, and 67.5 Gy in the salvage group. End-point of the study was the progression-free survival (PFS), biochemical relapse-free survival (BRFS), overall survival (OS) and toxicity. Results the median follow-up was 33 months. The 3-year PFS and BRFS was 85.2% and 82%, respectively. The factors associated with a worst PFS at the univariate analysis (UVA) were: high Gleason score, pT≥3, esRT, concomitant hormone therapy (HT), and pelvic RT. In particular, aRT and sRT reported a significantly higher 3- year PFS compared to esRT at the UVA (93%, 85.4%, and 74.1%; p=0.000). Nevertheless, at the multivariate analysis (MVA) only Gleason score, pT and concomitant HT remains significantly correlated with PFS. Treatment of the relapse was: HT in 43% cases, stereotactic body radiotherapy (SBRT) in 43% patients, and HT+SBRT in 14% patients. At the last follow-up 8 patients deceased since, only two of which by PCa progression. Grade 1-2 GU toxicity during RT was: urgency (36%), dysuria (23%), increased urinary frequency (12.1%), and urinary retention (11.8%). Nevertheless, the majority of symptoms were present at the baseline. Grade 3 severe toxicity was represented by 10 (3.2%) cases of incontinence and 3 (1%) cases of urgency. The incidence of any-grade RT-related GU toxicity was significantly higher in the aRT group than the salvage group (esRT + sRT) (83.8% versus 64.5%). When comparing the incidence of any-grade RT-related GU toxicity in the aRT, esRT, and sRT groups we observed a significant correlation favoring sRT, over esRT, and aRT. Conclusion mild-hypofractionated RT seems to be safe and to provide local control rates similar to conventionally fractionated regimens at three-year follow-up. Hypofractionated early-salvage radiotherapy reported similar results as the adjuvant regimen, and confirms its safer toxicity profile. No unexpected severe toxicity was