ESTRO 2024 - Abstract Book

S2362

Clinical - Urology

ESTRO 2024

Conclusion:

This study confirmed the feasibility and safety of adaptive MRgRT on a 1.5T MR-LINAC in post-prostatectomy PC patients. Both acute and late toxicity and outcome were reported, suggesting the favorable toxicity profile and encouraging clinical outcomes, but yet to be further validated in future studies.

Keywords: prostate bed irradiation, MR-guided radiotherapy

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Digital Poster

Preliminary Outcomes of Hypofractionated Post-Prostatectomy 1.5T MR-guided Salvage Radiotherapy

Darren MC Poon 1 , Jing Yuan 2 , Oi Lei Wong 2 , Bin Yang 3 , Sin Ting 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:

Hypofractionation, as opposed to conventional fractionation, as post-prostatectomy salvage radiotherapy (SRT) provides patients (pts) with shorter and more accessible courses of treatment. However, one of the challenges for hypofractionated SRT is the substantial interfractional geometric variation of the clinical target volume (i.e. prostate bed and/or pelvic lymphatics) and adjacent organs-at-risk, We hypothesize that MR guidance could further improve outcomes of SRT by taking the advantages of superior MR image resolution and online adaptation on an MR-LINAC. Thus, this single-institutional study prospectively reports the preliminary clinical experiences and outcomes of hypofractionated MR-guided salvage radiotherapy (Hypo-MRgSRT) with 1.5T MR-LINAC in pts with post prostatectomy recurrence.

Material/Methods:

During Feb 2021-Jun 2023, 60 consecutive post-prostatectomy PC pts with biochemical recurrence were recruited. Staging PSMA-PET scans were allowed, and pts with radiological recurrence at prostate bed +/- nodes and/or pelvic bone, but not distant or visceral metastases, were included. Patients who underwent adaptive MRgSRT on a 1.5T MR-LINAC with moderate hypofractionation (20 fractions), but not conventional fractionation, were included. Androgen deprivation therapy (ADT) was allowed and prescribed at the discretion of the physician.. Hypo-MRgSRT was delivered with a total dose of 52.5-55Gy to prostate bed, 44 Gy to pelvic lymphatics, and 60 Gy to PSMA-PET detected local recurrence and nodal/pelvic bone metastases in 20 fractions with daily online adaptation. Margins were set as per clinical guidelines. Regarding online adaptation, adapt-to-position (ATP) was the default setting with priority for maximizing workflow efficiency. Adapt-to-shape (ATS) was triggered when the center-customized