ESTRO meets Asia 2024 - Abstract Book

S288

Interdisciplinary – Urology

ESTRO meets Asia 2024

Due to strict adherence to OARs constraints, in T3b patients a slightly lower boost dose was feasible than in patients T2-T3a patients. The impact of intra-fraction motion on the accumulated D98% was about 1 Gy. This suggests that focal dose-escalation of >40 Gy to the intra-prostatic lesion is feasible for patients with locally advanced prostate cancer using MRI-guided online adaptive radiotherapy.

Keywords: MR-Linac, prostate, dose accumulation

265

Digital Poster

Early outcome of first Vietnamese series of moderately hypo-fractionated prostate cancer radiotherapy

Basma MBAREK, Thu Nguyen Huynh Ha, Duong Tran Anh, Tin phang duc Tin, thao vo

oncology, FV HOSPITAL, HCMC, Vietnam

Purpose/Objective:

The prostate cancer’s (PC) incidence rose in Vietnam from 2.2 per 100.000 patients in 2000 to 12.2 per 100.000 in 2020 1 resulting in a raising need radiotherapy with a subsequent increase in the radiotherapy departments workload. The moderately hypo-fractionated (MoHF) protocols according to results of the published clinical trials, based on to the low alpha/beta ratio of PC cells, offer an alternative shorter treatment course more convenient for patients and families as well as to department workload. Subsequently, MoHF protocol for our PC has been implemented in our department using the Volumetric Arc Modulated Therapy (VMAT) with Image Guided Radiation Therapy (IGRT). This is to our best knowledge the first Vietnamese series. From May 24 th 2021 to June 30 th 2023, 23 patients were treated by MoHF radiotherapy protocols for PC. Initially, we implemented protocol of 60Gy in 20 fractions (60Gy/20fx) for intermediate-risk PC patients. Since the release of data of PCS5 trial 2 in the end of 2022 about protocol of 68Gy in 25 fractions (68Gy/25fx) for high-risk PC patients, this protocol was also implemented for our high-risk cases since December 2022. The institutional protocol for treatment of PC includes full bladder, injected computer tomography simulation (CT SIM) with 2,5 mm slice thickness. The organs at risk (OARs) as well as the clinical target volume (CTV) are delineated according to the RTOG atlases. The CTV to planning target volume (PTV) margins are 5mm in all direction except posterior margin that was limited to 3mm. The threshold to apply the shift after matching the images of the daily Cone Beam Computer Tomography (dCBCT) was 2mm. A weekly consultation during radiotherapy and during the months following the treatment. The side effects were graded according to the CTCAE V3.0. The average duration to complete the radiotherapy treatment planning (from the day of CT-SIM to the day of quality assurance) for these cases in study was 7 days. For the dose constraint achievement, 100% of planning had D2% < 107% of dose prescription while 21/23 plannings (91.30%) achieved the standard criteria of PTV coverage as well as organs at risk protection. The remaining 2/23 plannings (8.70%) were validated with a minor variation in either target coverage or OARs constraints (Table 1). The most common acute GU and GI radiotherapy toxicity was respectively dysuria and rectal frequency which happened on 21/23 cases (91.30%) and 19/23 cases (82.6%) with grade 1 or 2. All acute side effects were solved in 100% of patients within 1 month after completion of treatment. No grade 3 or higher acute or late toxicity was reported. Material/Methods: Results: