ESTRO 2024 - Abstract Book

S2111

Clinical - Sarcoma, skin cancer, melanoma

ESTRO 2024

2. Srikanthan A, Leung B, Shokoohi A, Smrke A, Bates A, Ho C. Psychosocial Distress Scores and Needs among Newly Diagnosed Sarcoma Patients: A Provincial Experience. Sarcoma. 2019 Jul 1;2019:5302639. doi: 10.1155/2019/5302639. PMID: 31354383; PMCID: PMC6636442.

3. Buche, H, Michel,A., Blank, N. (2022) Use of virtual reality in oncology: From the state of the art to an integrative mode, Frontiers of Psychology,https://doi.org/10.3389/frvir.2022.894162

2169

Mini-Oral

Partially Ablative Body Radiotherapy (PABR): A novel approach for unresectable sarcomas

Kelvin Yu 1,2 , Sarat Chander 1 , Samuel Ngan 1 , Julie Chu 1 , David Chang 1 , Shankar Siva 1,3 , Aaron Wong 1,3 , Adam Yeo 1,3 , Tomas Kron 1,3,4 , Nick Hardcastle 1,3,4 , Mathieu Gaudreault 1,3,4 , Therese Chesson 1 , Siena Williams 1 , Mark Burns 1 1 Peter MacCallum Cancer Centre, Department of Radiation Oncology, Melbourne, Australia. 2 University of Santo Tomas Hospital, Department of Radiation Oncology, Manila, Philippines. 3 The University of Melbourne, The Sir Peter MacCallum Department of Oncology, Melbourne, Australia. 4 University of Wollongong, Centre for Medical Radiation Physics, New South Wales, Australia

Purpose/Objective:

Locally advanced, bulky, and unresectable sarcomas cause significant tumour mass effects, leading to burdensome symptoms. Conventional palliative radiotherapy is often limited by the potential toxicities to surrounding organs, resulting in suboptimal response and limited symptomatic benefit. We have developed a novel technique termed Partially Ablative Body Radiotherapy (PABR) to deliver a high, ablative dose to the tumour core and a low, palliative dose to its periphery in order to improve tumour and symptomatic response. We consider PABR a type of Spatially Fractionated Radiation Therapy (SFRT) which could utilise vascular damage, radiation-induced bystander effect (RIBE) and immune-mediated abscopal effects to improve tumour cell killing in the low-dose area. We postulate that PABR will increase overall tumour response in unresectable sarcomas without significantly increasing treatment toxicity. This study aims to report the safety and oncologic outcomes of PABR in patients with bulky, unresectable STS.

Material/Methods:

This retrospective cohort study included patients with histologically proven sarcoma treated with PABR at our institution from January 2020 to October 2023. For the PABR protocol, 20Gy in 5 fractions to the whole tumour with an intratumoral boost dose of 50Gy was delivered over five fractions using Volumetric Modulated Arc Therapy with simultaneous integrated boost (VMAT-SIB). The patient immobilisation and RT delivery were done according to the institutional protocol, which varied depending on the site of the disease. For target delineation, diagnostic CT/MRI and/or PET-CT were fused with the planning scan and the gross tumour volume (GTV2000) was contoured. A 1cm isotropic margin expansion was then applied to generate the Planning Target Volume (PTV2000). Next, a 1.5-2cm isotropic contraction from the GTV was applied to form the GTVboost5000 inside the intact GTV. The rationale for