ESTRO 2024 - Abstract Book

S4585

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

[2] Korevaar EW , Habraken SJ, Scandurra D, Kierkels RG, Unipan M, Eenink MG, Steenbakkers RJ, Peeters SG, Zindler JD, Hoogeman M, et al ., “Practical robustness evaluation in radiotherapy–a photon and proton-proof alternative to ptv-based plan evaluation”, Radiother Oncol 2019;141,S267–74

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Development of non-coplanar VMAT planning for SABR spine

Amy Cottom 1,2 , Andrew Willett 1 , Robyn Stansbridge 1

1 The Clatterbridge Cancer Centre, Radiation Physics, Liverpool, United Kingdom. 2 The University of Liverpool, Physics, Liverpool, United Kingdom

Purpose/Objective:

This study aimed to determine if non-coplanar arcs could improve target coverage and increase the dose gradient to the proximal CNS organs at risk (OAR) for SABR spine patients, when compared to coplanar techniques. Existing literature for other treatment sites suggests that increasing the degrees of freedom through non-coplanar arcs can improve target coverage whilst sparing dose to the surrounding OARs (Smyth et al, 2016) (Yu et al, 2016). However, there is currently limited research into non-coplanar techniques for SABR spine. This project involved two phases: first, finding an optimal non-coplanar field arrangement; second, a planning study. Since non-coplanar planning is not a locally used treatment method for spine metastases, there is currently no optimal class solution for determining the number of arcs and treatment couch angles. Therefore, an iterative and manual process was adopted (Simms et al, 2022) and applied to a retrospective cohort of patients to determine an optimal field arrangement. This field arrangement was applied to an independent set of SABR spine patients to compare coplanar and non-coplanar techniques using chosen plan quality metrics.

Material/Methods:

Ten patients previously treated using SABR with a prescription of 27Gy/3# were included in this study. Five of these patients were used to determine an optimal field arrangement by evaluating plans, using a maximum of 11 non coplanar arcs. A manual and iterative process was applied to progressively narrow down the selection based on the contributing monitor units. Plan quality metrics, including Paddick’s Conformity Index (Paddick, 2000), D95% and D99% of the PTV, dose gradient from the PTV to the isocentre (mid-cord), and maximum dose 0.2cm from the PTV, were investigated to determine the number of optimal non-coplanar fields. This field arrangement was then applied to the remaining five patients and compared to coplanar techniques. Plan quality metrics, such as those predefined, were investigated along with the maximum dose to the target, low dose bath and plan complexity.

Results: