ESTRO 2024 - Abstract Book

S5988

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

Keywords: MRgRT, Adaptive Radiotherapy, Contouring

1878

Proffered Paper

Early experience with GTV boost for prostate cancer: a comparison of MR-Linac and HDR brachytherapy

Amanda Moreira 1 , Jennifer Dang 1 , Vickie Kong 1,2 , Bernadeth Lao 1 , Jeff Winter 1,2 , Robert Weersink 1 , Rachel Glicksman 1,2 , Alejandro Berlin 1,2 , Srinivas Raman 1,2 , Andrew McPartlin 1,2 , Peter Chung 1,2 1 Princess Margaret Cancer Centre, Radiation Medicine Program, Toronto, Canada. 2 University of Toronto, Department of Radiation Oncology, Toronto, Canada

Purpose/Objective:

MR-guided high dose rate (HDR) brachytherapy for focal GTV boost in prostate cancer radiotherapy is a well established technique at our institution. Potential disadvantages are the resource-intense, invasive nature of the procedure and lack of applicability for some patients where brachytherapy is contraindicated. New linear accelerators with integrated MRI have enhanced soft tissue contrast, allowing visualization of the GTV within the prostate, hence facilitating the use of External Beam Radiation Therapy (EBRT) to deliver GTV boost. This study compared patient reported acute toxicity between the two techniques

Material/Methods:

Twenty intermediate risk prostate cancer patients who were enrolled and treated between May 2022 and August 2023 in prospective clinical trials were included in this study. 10 patients received GTV boost fraction using HDR brachytherapy with a median of 7 brachytherapy catheters (range 3-9), and 10 patients were treated with EBRT using a 1.5T MR-Linac. For HDR treatment patients were positioned supine under general anesthesia while transperineal catheters were inserted under MRI guidance. The procedure then included contouring, plan optimization, QA process and HDR delivery with a median procedural time of 158 minutes (range of 142-207 minutes). For EBRT treatment patients were positioned supine with minimal immobilization and an empty bladder. Daily procedure MR imaging, contouring, plan optimization, re-imaging (followed by further optimization as applicable), QA process and finally beam delivery with a median duration of 53 minutes (range of 42-68 minutes). PTV margin for GTV was 2mm all around except 4 mm superior-inferior for HDR patients and 4mm all around except for 3mm right-left for MRL patients. All patients received 1x15 Gy to the GTV followed within 1 week by 5x6 Gy (alternate days) to the whole prostate (PTV margins were 5mm for all patients). Both groups received their subsequent whole gland prostate treatment on the MR-Linac. Common Terminology Criteria for Adverse Events (CTCAE v 4.0) were collected weekly from the start of treatment to one month follow-up. Incidence of adverse events (AE) as well as grade were compared between the groups. Patient-reported quality of life was captured using The Expanded Prostate Cancer Index Composite (EPIC) survey. The questionnaire was administered at baseline and at one month follow-up. Results were analyzed using descriptive statistics.