ESTRO 2025 - Abstract Book

S2843

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Pedone, C. et al .” Preoperative short-course radiation therapy with PROtons compared to photons in high-risk RECTal cancer (PRORECT): Initial dosimetric experience”. Clin Transl Radiat Oncol 2023

2949

Digital Poster Development of lattice radiotherapy methodology as preparatory work for phase I clinical trial Francesca Fiorini 1 , Thomas Satherley 1 , Abdul Khalid 2 , Adam Aitkenhead 2,3 , Matthew Clarke 2 , Geoffrey Higgins 4 , Matthew Lowe 2 , Maxwell Robinson 1 , Kristoffer Petersson 4 1 Radiotherapy Physics, Oxford University Hospitals NHS Trust, Oxford, United Kingdom. 2 Radiotherapy, The Christie NHS Foundation Trust, Manchester, United Kingdom. 3 Manchester Academic Health Science Centre (MAHSC), University of Manchester, Manchester, United Kingdom. 4 Oncology, University of Oxford, Oxford, United Kingdom Purpose/Objective: Spatially fractionated radiotherapy (SFRT) diverges from conventional practice as it involves the delivery of an intentionally inhomogeneous dose to the tumour [1]. Variation is delivered as a lattice or grid of high-dose islets surrounded by low dose areas. Literature is sparse in defined standard SFRT methodology, but an “ideal” SFRT dose delivery could be considered to have a dose distribution with a normal fraction dose of ~2 Gy in the PTV low dose areas and peak dose areas reaching doses ~20Gy. It has been suggested that SFRT might improve the therapeutic ratio between tumours and surrounding normal tissues arising from a more effective immunological response compared with conventional RT [2,3]. We present a research study developing and validating a lattice methodology as part of preparatory work for phase one clinical trial. Principal aims were to: 1. Establish a method for creating optimal SFRT plans, e.g. optimise the size, distance, number, and positions of islets to produce a desired SFRT dose distribution. 2. Establish planning constraints or metrics with defined priority to review the acceptability of SFRT plans. 3. Identify suitable patients where SFRT treatments would be possible according to the method and constraints defined above. Material/Methods: We retrospectively audited all palliative RT patients treated at our local centre in a recent six-month period for suitability for inclusion within the study as potential SFRT patients. Bone and organ confined disease cases were excluded. Suitable soft tissue cases where GTV was contoured as part of clinical treatment were assessed. GTVs that were non-diffuse and had a volume of at least 100 cm 3 were deemed suitable for inclusion as prospective SFRT cases. Results: 20 cases were identified and planned with developed lattice methodology achieving the dose constraints in table one. Dosimetric validation measurements were performed for a subset of cases. Figure one shows an illustrative typical case. SFRT planning constraints and relative priorities are shown in table one. We further present a summary of resulting achieved planning constraints.