ESTRO 2025 - Abstract Book

S65

Invited Speaker

ESTRO 2025

We conducted group discussions with a specialist expert IGRT team to identify themes of current re-irradiation challenges, and ways in which IGRT protocols could be optimised. This will be discussed during the presentation. Themes such as communication between team members, technical planning considerations, the need for individualised approaches, imaging and verification techniques, and gaps in professional development were identified. Within these areas, RTTs can work together with the MPT to improve safety, accuracy and outcomes.

4750

Speaker Abstracts Brachytherapy-boost or EBRT-boost: Current evidence David Buchser Garcia Radiation Oncology, Cruces University Hospital, Barakaldo, Spain

Abstract:

Dose escalation has emerged as a cornerstone of curative-intent radiotherapy for prostate cancer, offering significant improvements in biochemical control and overall survival. In contemporary practice, brachytherapy boost (BT-boost) in an established strategy for delivering escalated doses, particularly in intermediate- and high-risk disease whereas external beam radiotherapy boost (EBRT-boost) is been evaluated as a less invasive alterantive. This presentation aims to review and contrast the current evidence supporting each approach, with a focus on clinical outcomes, toxicity profiles, patient selection, and future directions. BT-boost techniques, using either low-dose-rate (LDR) or high-dose-rate (HDR) brachytherapy, enable delivery of a highly localized, ablative radiation dose directly to the prostate with steep dose gradients, thereby sparing adjacent organs at risk. Conversely, EBRT-boost strategies have evolved significantly with the advent of intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic body radiotherapy (SBRT), allowing precise dose escalation with improved conformity and reduced toxicity. Several key trials have evaluated the efficacy of BT-boost. The ASCENDE-RT trial, one of the most influential randomized studies in this domain, demonstrated a marked improvement in biochemical progression-free survival with the addition of LDR brachytherapy boost compared to dose-escalated EBRT alone. Further support comes from prospective and retrospective series, including work by Hoskin and Kishan, showing improved metastasis-free survival and biochemical control with BT-boost, particularly in high-risk patients. However, modern EBRT techniques—especially hypofractionated and ultra-hypofractionated regimens—have shown competitive results, with some series reporting comparable disease control rates while potentially minimizing toxicity. Toxicity and quality-of-life outcomes are central to decision-making when selecting a boost modality. BT-boost is associated with increased genitourinary (GU) toxicity, including urinary irritation and obstructive symptoms, although recent advances in real-time HDR techniques and imaging guidance may mitigate these effects. Gastrointestinal (GI) toxicity tends to be lower with BT-boost due to minimal rectal dose exposure. On the other hand, EBRT-boost typically results in lower acute GU toxicity but may carry a higher risk of late GI toxicity, particularly in the absence of rectal sparing strategies. The use of rectal spacers, adaptive planning, and improved imaging are emerging as key tools to reduce toxicity for both modalities. Patient selection remains a critical factor in optimizing outcomes. BT-boost may be most suitable for younger patients with high-risk disease and favorable anatomy, where the potential for enhanced local control outweighs the risk of GU side effects. EBRT-boost may be preferred for older patients, those with significant comorbidities, or when brachytherapy is contraindicated or technically challenging. In all cases, multidisciplinary collaboration is essential to tailor treatment plans to individual patient needs, balancing efficacy with safety and quality of life.