ESTRO 2024 - Abstract Book

S2360

Clinical - Urology

ESTRO 2024

803

Digital Poster

Post-prostatectomy Radiotherapy with MR-LINAC: Feasibility, Safety and Preliminary clinical outcome

Darren MC Poon 1 , Jing Yuan 2 , Oi Lei Wong 2 , Bing Yuan 3 , Sin Tin Chiu 4 , George Chiu 4 , Kin Yin Cheung 3 , Siu Ki Yu 3

1 Hong Kong Sanatorium and Hospital, Comprehensive Oncology Centre, Happy Valley, Hong Kong. 2 Hong Kong Sanatorium and Hospital, Research Department, Happy Valley, Hong Kong. 3 Hong Kong Sanatorium and Hospital, Medical Physics Department, Happy Valley, Hong Kong. 4 Hong Kong Sanatorium and Hospital, Radiotherapy Department, Happy Valley, Hong Kong

Purpose/Objective:

Post-prostatectomy RT is a potentially curative treatment for prostate cancer (PC) patients (pts) with biochemical recurrence or at high risk for recurrence. One of the biggest challenges for post-prostatectomy RT is the highly deformable nature of prostate bed and adjacent organ-at-risk, and the current CT or X-ray guidance with suboptimal soft tissue resolution may render patients with risk of geographical miss or increased toxicity. The introduction of integrated magnetic resonance (MR) imaging and linear accelerator (MR-LINAC) enables improved soft tissue delineation. Furthermore, its online adaptive planning in response to interfractional anatomical changes detected by daily MRI potentially enhance the therapeutic ratio with more precise target radiation and OAR sparing.. So far, the data regarding the post-prostatectomy MR-guided RT (MRgRT) is scarce. Thus, the purpose of this study is to prospectively report the feasibility, safety and preliminary clinical outcome of post-prostatectomy MRgRT on a 1.5 Tesla (T) MR-LINAC. From April 2020 to August 2022, consecutive post- prostatectomy PC pts (≥18 years) experiencing biochemical relapse or having high-risk pathological factors were prospectively recruited. Other inclusion criteria were: with or without a prostate bed or pelvic nodal/bony recurrence detected by PSMA-PET; MRI compatibility; no other cancer history; no previous prostate RT. Exclusion criteria were: distant or visceral metastases; MRI contraindication (e.g. claustrophobia, metal implants, etc); previous prostate or pelvic irradiation. The included pts underwent salvage or adjuvant MRgRT on a 1.5T MR-LINAC with a conventional daily 35-fraction scheme and a total dose of 70 Gy. Androgen deprivation therapy (ADT) was prescribed at the discretion of the physician. Concurrent dose of 70-77 Gy to PSMA-PET detected local recurrent/residual tumor, 52.5-56 Gy to lymphatics, and 60-77 Gy to nodal/bone metastases were also delivered. PTV margins are 8 mm (except 5mm in the posterior) for the prostate bed and 5 mm for lymphatics/nodal/bone, according to consensus guidelines. Adapt-to-position (ATP) was utilized with priority to maximize workflow efficiency while adapt-to-shape (ATS) was used only in the cases of violation of center customized protocol or dose criteria. Pts were followed and PSA levels were monitored at the completion date of MRgSRT, 1-month, 3-month, and every 6 months later. Toxicities were assessed using the Common Terminology Criteria for Adverse Events (CTCAE) v5.0. PSMA-PET was arranged if any post-RT biochemical recurrence. Biochemical progression-free survival (bPFS) and radiological progression-free survival (rPFS) were estimated using the Kaplan-Meier (KM) method. Material/Methods: