ESTRO 2023 - Abstract Book

S1253

Digital Posters

ESTRO 2023

Gastrointestinal

Genitourinary

Acute Toxicity

HF

CF

HF

CF

RTOG grade 4 0.0 % RTOG grade 3 0.0 % RTOG grade 2 46.7 % RTOG grade 1 40.0 % RTOG grade 0 13.3 %

0.0 % 0.0 % 1.3 % 2.9 % 37.6 % 20.0 % 54.8 % 57.1 % 6.4 % 20.0 %

0.0 % 0.0 %

31.8 % 57.3 %

10.8 % P = 0.71 and 0.04 for gastrointestinal and genitourinary toxicity, respectively. N = 105 for HF and 157 for CF Conclusion Moderately hypofractionated WBRT seems to provide a well-tolerated treatment of the pelvic lymph nodes within the first 2 years. Longer follow-up and CRTs are needed to provide further evidence.

PO-1544 Outcomes comparison using PSA cut-off values of 0.1 at 6 months in high-risk prostate cancer

A. Nabid 1 , N. Carrier 2 , A. Martin 3 , J. Bahary 4 , P. Vavassis 5 , B. Bahoric 6 , R. Archambault 7 , F. Vincent 8 , R. Bettahar 9 , M. Duclos 10 , L. Souhami 11 1 Centre hospitalier universitaire de Sherbrooke, Radio-oncologie, Sherbrooke, Canada; 2 Centre hospitalier universitaire de Sherbrooke, Biostatistique, Sherbrooke, Canada; 3 Centre hospitalier universitaire de Québec, Radio-oncologie, Québec, Canada; 4 Centre hospitalier universitaire de Montréal, Radio-oncologie, Montréal, Canada; 5 Hôpital Maisonneuve Rosemont , Radio-oncologie, Montréal, Canada; 6 Hôpital Général Juif de Montréal, Radio-oncologie, Montréal, Canada; 7 Hôpital de Gatineau, Radio-oncologie, Gatineau, Canada; 8 Centre hospitalier régional de Trois-Rivières, Radio-oncologie, Trois-Rivières, Canada; 9 Centre de santé et de services sociaux de Rimouski, Radio-oncologie, Rimouski, Canada; 10 McGill University Health Centre, Radiation Oncology, Montréal, Canada; 11 McGill University Health Centre, Radiation Oncolgy, Montréal, Canada Purpose or Objective To determine, in patients with high-risk prostate cancer treated with 36 vs. 18 months of androgen deprivation therapy (ADT) and radiotherapy (RT), whether a PSA ≤ 0.1 ng/ml at 6 months after the beginning of ADT, is predictive of a better clinical outcome and to compare those outcomes between 36 and 18 months of ADT. Materials and Methods We extracted data used from the PCS IV trial in which 630 patients were randomized to ADT of 36 vs. 18 months plus pelvic and prostate RT. We computed outcomes analyses only in patients who completed 18 or 36 months of ADT. Biochemical failure (BF), distant metastases (DM) and prostate cancer-specific mortality (PCSM) were analyzed with competing risks methods and overall survival (OS) and distant metastases-free survival (DMFS) rates with the Kaplan Meier method and the log-rank test. We examined the impact of PSA ≤ 0.1 at 6 months on outcomes. Results Results are reported with a median follow-up of 15.2 (IQR 13.2-18.8) years. 480/630 patients were available for the analyses. Of these, 43.8% (210) achieved a PSA ≤ 0.1 at 6 months Overall, patients with a PSA >0.1 at 6 months (56.2%) had significantly more BF (HRs (95% CI) = 2.44 (1.71-3.50), p<0.001), DM (HRs = 2.78 (1.57-4.92), p<0.001), and PCSM (HRs = 2.33 (1.30-4.17), p=0.005) than those with PSA ≤ 0.1. No difference was seen in OS and DMFS. In patients receiving 36 months of ADT (167/310), 44.3% (74/167) achieved a nadir of ≤ 0.1 at 6 months compared to 43.4% (136/313) of the 97.8% (313/320) receiving 18 months. Among patients achieving a PSA ≤ 0.1 at 6 months, no significant differences were seen between ADT of 36 vs 18 months in all outcomes measured. In patients with PSA > 0.1 at 6 months those receiving 18 months of ADT, compared to 36 months, developed higher rates of BF [46.3% vs. 26.9%, HRs = 2.02 (1.30-3.14), p=0.002] and DM [22% vs. 11.8%, HRs = 1.93 (0.99 3.75), p=0.054]. No significant difference was observed in PCSM, OS and DMFS between groups. Conclusion These data suggest that in high-risk patients achieving a PSA nadir ≤ 0.1 at 6 months, 18 months of ADT appears sufficient. Patients remaining with a higher PSA after 6 months of ADT may harbor a more aggressive genetic phenotype and should be considered for trials testing newer therapeutic strategies.

PO-1545 Can we spare the rectum during prostate radiotherapy?

F. piro 1 , B. ilaria 2 , C. daria 3 , M. luigi 4

1 Mariano santo, U.O. RADIOTHERAPY, cosenza, Italy; 2 Mariano santo, fisica, cosenza, Italy; 3 mariano santo, u.o. radiotherapy, cosenza, Italy; 4 Mariano santo, U.O. radiotherapy, cosenza, Italy

Purpose or Objective