ESTRO 2024 - Abstract Book

S5998

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

Initial Evaluation of Radiographer Target Volume Online Contouring for Bladder MRIgRT

Bethany Williams 1 , Jonathan Mohajer 1 , Sophie Alexander 2 , Helen Barnes 1 , Shabanaz Boodhoo 1 , Francis Casey 1 , Joan Chick 1 , Alex Dunlop 1 , Trina Herbert 1 , Robert Huddart 2 , Manasi Ingle 2 , Jayde Nartey 1 , Simeon Nill 2 , Priyanka Patel 1 , Gillian Smith 1 , Hubert Stankiewicz 1 , Shaista Hafeez 2 , Helen McNair 1 1 Royal Marsden NHS Foundation Trust, Radiotherapy, London, United Kingdom. 2 Royal Marsden NHS Foundation Trust and Institute of Cancer Research, Radiotherapy, London, United Kingdom

Purpose/Objective:

MRI guided radiotherapy (MRIgRT) using the Elekta Unity MR Linac (MRL) (Elekta AB, Stockholm, Sweden), presents promising advancements in accounting for inter- and intra-fractional changes in adaptive bladder radiotherapy. Where extensive population-based margins have conventionally been applied, soft tissue definition of MRI and daily online adaptive treatment planning facilitates reduction in exposure of normal tissue and developments in dose escalation (1) . One barrier to wider clinical implementation is resource intensity; specifically, the requirement for clinicians to perform target volume and organ at risk contouring at each fraction. Releasing clinicians from this role has the potential to improve the cost-consequence and machine capacity of the MRL, while increasing the scope of practice of the therapeutic radiographer (RTT). Alongside plan approval delegation to physicists, RTT online contouring has been successfully implemented for prostate MRIgRT, requiring clinician’s attendance at fraction one only (2) . We report our initial results of a service evaluation of RTT online contouring for patients receiving 55.0Gy in 20 fractions for whole bladder MRIgRT. RTTs undertook a contouring training programme for whole bladder MRIgRT, created in collaboration with clinicians and physicists. The training package consisted of educational presentations, 10 offline cases contoured and reviewed by a clinician, five online observations of clinician contouring, and five sessions of online contouring supervised by a clinician. Online treatment plan dosimetric criteria were approved by clinicians, enabling a delegated operator (physicist) to authorise an online plan and clinician-independent treatment. RTT contoured and clinician contoured treatment fractions were timed. In offline analysis, the alternate profession was asked to contour the same session image. Interobserver variability between RTT online contours and offline clinician CTV and PTV contours, and vice versa, were assessed using Dice Similarity Co-efficient (DSC), Hausdorff distance (HD) and Mean Distance to Agreement (MDA) on Raystation TPS (RaySearch Laboratories, Stockholm, Sweden, V.12.0.0.932). Dosimetric analysis was performed using offline treatment planning system (Monaco TPS, Elekta AB, Sweden V5.40.01) whereby the online adaptive treatment plans contoured by RTTs were reported against clinician contours. Dosimetric criteria was reported and assessed against online dosimetric criteria. Material/Methods:

Results:

56 fractions from three patients prescribed 55.0Gy/20# to the whole bladder were analysed. 29 fractions were contoured online by one of two clinicians and 27 were contoured online by one of four RTTs in clinician-independent