ESTRO 2022 - Abstract Book

S480

Abstract book

ESTRO 2022

Conclusion ENRT with PET guided SIB for PCa LN relapses determines good CRFS and CSS. In field LN relapses were registered in only 2.85% (5/175 ) of patients.

MO-0554 Pelvic dose accumulation from time-successive prostate and lymph node radiation (NCT02274779)

L. Vaugier 1 , V. Guimas 1 , S. Chiavassa 2 , G. Delpon 2 , S. Supiot 1

1 Institut de Cancérologie de l'Ouest, Radiation Oncology, Saint Herblain, France; 2 Institut de Cancérologie de l'Ouest, Radiophysics, Saint Herblain, France Purpose or Objective Pelvic lymph node (PLN) relapses of prostate cancer is a frequent scenario for which salvage pelvic radiotherapy (PLN-RT) is commonly proposed, even for patients with prior prostate radiotherapy (P-RT). Regarding the OAR in the pelvis, the management of the radiation field junction with prior P-RT remains an issue, since the dose accumulation may exceed the value commonly recommended for one radiation course. Our objective is to report on the dose accumulation for the pelvic OAR and the organ-related tolerance based on the prospective OLIGOPELVIS GETUG-P07 trial. Materials and Methods OLIGOPELVIS GETUG-P07 trial was a prospective multicenter phase 2 trial, whose efficacy and tolerance (CTCAE v4 and EORTC questionnaires) were already proven. The prescribed dose was 54 Gy/1.8 Gy fractions with up to 66 Gy/2.2 Gy fractions to the pathologic PLN. We focused on the patients with prior P-RT history. Based on international recommendations, following pelvic organs (bladder, rectum, sigmoid, ureter, lumbosacral plexus) were centrally delineated on both P-RT and PLN-RT CT scans. Rigid and deformable registrations were performed in order to enable physical dose summation. The quality of the registration was assessed by the calculation of Dice Similarity Coefficient (DSC).

Results Thirty-three patients (30 with prior salvage prostatic bed and 3 with prior prostate conservative radiotherapy), were included. The median P-RT dose was 66 Gy and 76 Gy in 2 Gy fractions for prostatic bed and prostate radiotherapy, respectively. The median time interval with PLN-RT was 50 months. With rigid registration, median DSC were 0.3, 0.3, 0.2,