ESTRO 2022 - Abstract Book

S683

Abstract book

ESTRO 2022

The present prospective study (NCT04703543) was conducted at a single Institution between August 2017 and June 2020. Eligibility criteria were: undetectable prostate specific antigen (PSA) after RP; biochemical recurrence (2 consecutive PSA rises to 0.2 ng/ml or greater); a presumed local failure at DCE-MRI (early/fast enhancing discrete lesion on DCE sequences); no distant metastases at choline-PET/CT; no previous history of androgen deprivation therapy and/or RT. Accrued patients underwent sRT as it follows: 66-69 Gy/30 fractions to the prostatic bed, 73.5 Gy/30 fractions to the local failure at DCE-MRI, 54 Gy/30 fractions to the pelvic nodes (when treated). All patients were offered DCE-MRI 3 months after sRT, and repeated at 3-month intervals until complete disappearance or a maximum of 4 scans. The endpoint of the study, complete response (CR), was defined as the complete disappearance of the target lesion at DCE-MRI. In case of misses before CR, the observation was considered as a persisting partial response (PR). Results 62 patients with 72 nodules at DCE-MRI were accrued. All patients underwent the 1 st DCE-MRI at a median of 3.3 months (IQR: 3.1-4.1) after sRT, 33 patients (53.2%) presented a CR, 27 (43,5%) a PR, 2 (3.2%) no response. One patient, implanted with a cardiac device, did not undergo further MRI. Three more patients declined further testing after the 1 st (N=2) or the 2 nd (N=1) re-evaluation due to the COVID-19 pandemic. Twenty-eight patients underwent a 2 nd DCE-MRI after a median of 6.8 months (IQR: 6.5-7.6) from sRT, 20 had a CR, 8 had a PR. After a median time of 10.7 months (IQR: 10.6-12.6), 6 patients were scanned for a 3 nd DCE-MRI: 4 CR, 2 PR. The last patient reported a CR after 16.7 months. The majority (94.3%, 95%CI: 88.0-100.0%) of lesions had completely disappeared by the 3 rd re-evaluation or a median time of 10.7 months from the end of sRT (Figure).

Independent predictors of CR at 1 st re-evaluation on multivariable analysis were: the volume of the lesion at pre-sRT DCE- MRI (OR 0.076, 95%CI 0.009-0.667; p =0.02), the time of re-evaluation from treatment (OR 3.39, 95%CI 1.156-9.993; p =0.026) and the PSA percent decrease at the 5 th week of sRT (OR 1.02, 95%CI 0.999-1.050; p = 0.058) (Table).

Receiver-operating characteristic curve (ROC) analysis identified the best cut-off on CR for baseline volume at 0.545 cc, AUC 0.683 (95%CI: 0.548-0.818, p =0.014). The probability of a CR for lesions larger than the cut-off identified at ROC analysis was only around 75% at 10.7 months. Conclusion The vast majority of local lesions disappears at DCE-MRI after sRT, though larger lesions may require more than 10 months from treatment end.

OC-0767 Machine learning-based models for prediction of erectile dysfunction in localized prostate cancer

H. Hasannejadasl 1 , C. Roumen 1 , H. van der Poel 2 , B. Vanneste 3 , J. van Roermund 4 , K. Aben 5,6 , P. Kalendralis 7 , B. Osong 7 , L. Kiemeney 5 , I. Van Oort 8 , R. Verwey 9 , L. Hochstenbach 10 , E. J. Bloemen- van Gurp 9,11 , A. Dekker 1 , R. Fijten 7