ESTRO 2024 - Abstract Book

S4105

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

References:

[1] RS Thing, R Nilsson, S Andersson, M Berg, M D Lund, "Evaluation of CBCT based dose calculation in the thorax and pelvis using two generic algorithms", Phys Med. 2022 Nov:103:157-165.

2795

Poster Discussion

Analysis of workflow choice for MR-Linac prostate patients: adapt-to-shape vs adapt-to-position

Denis Page 1 , Ananya Choudhury 1,2 , Tomas Janssen 3 , Danny Vesprini 4 , Brian Keller 4 , Shaista Hafeez 5 , Alison Tree 6 , Lenny Verkooijen 7 , Jochem van der Voort 7 , Cornelis van den Berg 7 , Robert Chuter 1,8 , Eliana Vasquez Osorio 1 , Alan McWilliam 1 1 University of Manchester, Radiotherapy Related Research, Manchester, United Kingdom. 2 The Christie NHS Foundation, Clinincal Oncology, Manchester, United Kingdom. 3 The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, Netherlands. 4 Sunnybrook Health Sciences Centre, Department of Radiation Oncology, Toronto, Canada. 5 The Royal Marseden NHS Foundation Trust, Uro-oncology, London, United Kingdom. 6 The Royal Marseden NHS Foundation Trust, Radiotherapy, London, United Kingdom. 7 UMC Utrecht, Imaging and Oncology, Utrecht, Netherlands. 8 The Christie NHS Foundation, Medical Physics and Engineering, Manchester, United Kingdom MRI provides superior soft tissue contrast compared to CBCT, without the use of ionising radiation. The MR-linac (MRL) facilitates daily plan adaptation, providing potential improvements in dose coverage for patients with OARs in close proximity to target volumes when compared to daily IGRT on conventional linacs [1]. Plan adaptation is achieved using an IGRT-like adapt-to-position (ATP) or fully adaptive adapt-to-shape (ATS) workflow. ATP uses rigid registration to adjust beam weight and/or shape whereas ATS is akin to daily replanning, utilising deformable registration, contour propagation and/or manual re-contouring. However, the ATS workflow necessitates longer treatment session times, ~60% longer than ATP [2], increasing demands on staff availability for recontouring and reducing patient comfort. In this work, we investigate the magnitude of the benefit of using ATS over ATP for two OARs and target volumes of prostate cancer patients, and analyse if differences in delivered dose are driven by anatomical changes during treatment. Purpose/Objective:

Material/Methods:

We established a method for evaluating the dose accumulated in the bladder, rectum, PTV and CTV across treatment, acknowledging that it must be applicable for the data collected during both ATS and ATP workflows (Figure 1(a)). This method consisted of non-rigidly registering daily anatomy to the planning scan, where structures are always available in both workflows, to create a deformable vector field (DVF) which represents the deformation between the two scans. The DVF is then applied to the dose from each workflow, with dose accumulation evaluated on the structure set.