ESTRO 2025 - Abstract Book

S386

Brachytherapy - Urology

ESTRO 2025

multicenter analysis evaluating tumor control and late toxicity after brachytherapy and external beam radiotherapy in 1293 patients. Strahlenther Onkol. 2024 Aug;200(8):698-705.

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Digital Poster Single-insertion multi-fraction HDR brachytherapy for prostate cancer: feasibility and short-term outcomes in a lower-middle-income country setting Carl Jay E. Jainar 1 , Patricia J. Ong 1 , Vannesza Hendricke C. Chua 1 , Stellar Marie R. Cabrera 1 , Sigfred R. Alpajaro 2 , David T. Bolong 2 , Roderick P. Arcinas 2 , Warren R. Bacorro 1,3 1 Department of Radiation Oncology, Benavides Cancer Institute, University of Santo Tomas Hospital, Manila, Philippines. 2 Department of Surgery, Section of Urology, University of Santo Tomas Hospital, Manila, Philippines. 3 Department of Clinical Epidemiology, Faculty of Medicine and Surgery, University of Santo Tomas, Manila, Philippines Purpose/Objective: High dose rate brachytherapy (HDR-BT), despite its excellent dosimetry, radiobiological advantages, and favorable therapeutic index 1,2 , remains underutilized for prostate cancer (PrC) in lower-middle-income countries (LMICs). Logistic and technology requirements limit adoption of no-patient-transfer workflows in these settings. We previously reported our experience with single-insertion multi-fraction (SIMF) HDR-BT in cervical cancers 3 , we now report its feasibility and short-term outcomes in prostate cancers treated in a tertiary academic hospital in the Philippines. Material/Methods: We reviewed adult patients with newly diagnosed, biopsy-confirmed, localized PrC treated with SIMF HDR-BT as monotherapy or boost. At our institution, dosimetry prioritized coverage of locations of MRI-defined nodules without image fusion. Patient demographics, disease characteristics, treatment parameters, and follow-up outcomes were retrieved. Toxicities were graded using CTCAE v5.0. With recent acquisition of fusion capability, we retrospectively determined the doses to these lesions (GTV_Dx) using five randomly selected cases. Results: Between June 2019 and September 2024, 28 patients were treated with SIMF HDR-BT. The median age was 67 years (range: 54-83), median PSA 11.23 ng/mL (range: 5-94.3), and median prostate volume 48.09 cc (range: 26.29-102.08). Four (14%) were low-risk, 12 (43%) intermediate-risk, and 12 (43%) high-risk. Of these, 20 (71%) received HDR-BT as a boost (6-6.5 Gy ×4) with 50 Gy external beam radiation therapy (EBRT), while 8 (29%) received HDR-BT monotherapy (6.5-8 Gy ×6). Median prostate D90 was 6.47 Gy for the boost group and 7.37 Gy for the monotherapy group. In the random sample, the GTV_Dx D90 was 8.93 Gy for monotherapy (n=1), and the median GTV_Dx D90 was 8.05 Gy in the boost group (n=4), with a total EQD2 of 137.9 Gy (α/β=1.5) (Figure 1). Institutional brachytherapy parameters are reported in Table 1. Acute toxicities were grade 1-2, with genitourinary (GU) toxicities reported in 15 (52%) patients and gastrointestinal (GI) toxicities in 7 (24%). No grade 3 or higher toxicities were observed. No procedural complications were documented. At the latest follow-up, only one patient (3%) had biochemical failure (PSA ≥ 2 ng/mL from nadir). The SIMF setup reduced treatment costs by approximately USD 1,200 (-23%) compared to a simulated two-insertion protocol.