ESTRO 2024 - Abstract Book

S5965

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

1 Azienda Ospedaliera Universitaria Careggi, Department of Allied Health Professions, Florence, Italy. 2 Azienda USL Toscana Centro, Department of Allied Health Professions, Prato, Italy. 3 Azienda Ospedaliera Universitaria Careggi, Radiation Oncology Unit, Florence, Italy

Purpose/Objective:

Breast radiotherapy represents a significant part of the workload in many radiotherapy departments. In a typical workflow, the Radiation Oncologist (RO) delineates the target volume and organs at risk (OARs) in breast cancer patients. However, radiation therapists (RTTs) are increasingly involved in clinical targets and the delineation of OARs has increased in recent years to improve workflow. Contouring OARs, and breast volumes in particular, is associated with considerable uncertainty. The purpose of this study was to compare the OAR delineations between RTTs and ROs in breast cancer patients and to measure inter-observer variability.

Material/Methods:

All RTTs involved in this study received training on delineation, delivered by an experienced RO. The training included classroom sessions and practical training. A total of 85 planning Computed Tomography (CT) image sets from patients undergoing breast radiotherapy were included in this study. In each CT image set, the contralateral breast, heart and both lungs were contoured independently by 3 ROs and 2 RTTs. Based on the contours created by the 3 ROs, gold standard contours (GS) were created using the majority vote algorithm with the software MIM Maestro and used as a reference for comparison with the contours drawn by 2 RTTs, named RTT1 and RTT2. The RTTs and the GS contours were compared using the Dice Coefficient (DSC) and Mean Distance Agreement (MDA). Statistical significance of the differences was tested using a Student’s paired t ‐ test (at the p = 0.05 significance level).

Results:

The analysis data obtained by comparison between GS vs RTT1 and RTT2 contours are summarized in Table 1. In particular, the mean DSC and MDA values of about 0.9 and 1 mm, respectively, for all structures delineated by both RTTs suggest the good overlap between the ROs and RTTs in contouring breast cancer patients. Despite the variability in breast volume contouring reported in the literature, the data obtained achieved a mean DSC > 0.88 and mean MDA ≤ 1.5 mm for both RTTs. The best overlaps were seen for lungs volumes (mean DSC=0.99 and mean MDA=0.1 mm). No statistical difference was observed comparing RTTs and GS for each OARs contours (p > .05).

Table 1: Mean and SD of DSC and MDA for each OAR obtain from comparison between GS and RTTs contours for all patients.