ESTRO 2024 - Abstract Book

S5973

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

Our study showed that regardless of the chosen contouring atlas, the prescribed organ-at-risk dose constraints were respected. However, ESTRO guidelines facilitated significantly lower doses to critical organs in particular for the lung and the thyroid, while maintaining correct coverage of the target volume. In our department, both atlases are used, depending on the tumor stage.

Keywords: ESTRO, RTOG, Breast

References:

Anjidani S, et al. A dosimetric comparative study following RTOG and ESTRO contouring guidelines for breast radiation therapy. Cancer Radiother. 2023 Sep;27(5):413-420.

1601

Proffered Paper

A quantitative analysis of online contour adaptation of the prostate CTV by RTTs on a 0.35T MR-Linac

Marjolein N Hilberts, Melissa AL Verdonk, Boaz Kalkhoven, An-Sofie E Verrijssen, Peter-Paul G van der Toorn, Tom CG Budiharto, Patricia FC Bronius, Diana Geerts, Coen W Hurkmans, Shyama U Tetar, Rob HN Tijssen

Catharina Hospital Eindhoven, Dept. of Radiation Oncology, Eindhoven, Netherlands

Purpose/Objective:

MR-guided radiotherapy facilitates daily contour adaptation. This allows a high precision treatment, but also increases the workload of the Radiation Oncologists (ROs). Shifting the task of online contour adaptation from ROs to Radiation Therapists (RTTs) would substantially decrease the ROs’ workload. The primary objective of this study is to examine whether RTTs' contour adaptations in prostate cancer (PCa) patients yield similar results to those performed by ROs. To our knowledge this is the first study that investigates this transition on a low-field 0.35T MR-Linac system.

Material/Methods:

First fraction data and baseline plans were retrospectively collected in 10 randomly selected low-intermediate risk PCa patients, treated with 5x7.25 Gy. Four ROs and four RTTs performed contour adaptation in a simulated, timed, adaptive workflow. All delineators had access to the baseline plan contours in a side-by-side view as per usual clinical workflow. Interobserver variability was assessed by quantifying the Dice similarity coefficient (DSC), Hausdorff distance (HD), and percentage volume differences of the adapted contours compared to the “gold standard”, defined by the CTV contours used in the patient's actual treatment. Further, a dosimetric analysis on the RTTs’ contours was conducted by optimizing the radiation plan to the RTTs’ contours and evaluating this plan on the clinically used (gold standard) contours. The dose-volume histogram (DVH) parameters were used to analyze the dosimetric effects of the variation in contour adaptations.