S2821
RTT - RTT education, training, and advanced practice
ESTRO 2026
require online delineation of the gross tumor volume (GTV) such as the TURBO trial (two fractions with GTV boost), the HypoFLAME III trial (5 fractions with GTV boost) and salvage radiotherapy have been implemented. Traditionally, GTV delineation required a radiation oncologist (RO) at each fraction. This abstract evaluates GTV contour quality and workflow timings in fully RTT-led MR-guided prostate treatments. Material/Methods: GTV delineation guidelines were developed in collaboration with ROs, using multiple imaging modalities including PSMA PET and multiparametric MRI (T2-weighted, DWI, and ADC sequences). RTTs were already trained in delineating the prostate CTV, bladder, and rectum as part of an RTT-led workflow using an in-house developed deformable image registration algorithm (Evolution)1 and deep-learning (DL) networks2 for prostate MR-guided radiotherapy. For GTV delineation, an additional one-hour focused training session was provided by an RO, focusing on PSMA PET and mpMRI interpretation for accurate GTV definition. After training, RTTs independently delineated the GTV in three retrospective patient cases using imaging and radiology reports. The delineations were compared among the RTTs and with those of the supervising RO, followed by peer-review discussions. Subsequently, RTTs performed online GTV delineations for five fractions under RO supervision. For the GTV evaluation, data from 19 patients (two fractions in the TURBO trial) were analyzed. Online GTVs delineations were compared with reference delineation using rigid registration (including rotations) in the prostate region between the reference scan and MR-Linac scans of fraction 1 and fraction 2. Dice similarity coefficient (DSC) scores, Hausdorff Distance (HD) and Mean Distance to Agreement (MDA) of the GTVs were compared. Treatment times were recorded. Results: The prostate GTV comparison showed a median DSC of 0.79, median HD of 2.9 mm and median MDA of 6 mm (Figure 1). Large deviations were found primarily for small GTVs and in case of large deformation due to inter-fraction rectal filling variation (Figure 2). Furthermore, the median total fraction time was 44 minutes (Figure 1).
Conclusion: The implementation of an RTT-led workflow for prostate GTV delineation at the MR-Linac has been demonstrated to be feasible and effective. Therefore, this RTT-led workflow has been successfully integrated in daily clinical practice within our department. Keywords: RTT-led, MR-Linac, Prostate GTV delineation References: 1. Bosma LS, Ries M, Denis de Senneville B, Raaymakers BW, Zachiu C. Integration of operator- validated contours in deformable image registration for dose accumulation in radiotherapy. Physics and Imaging in Radiation Oncology. 2023; 27:100483. 2. van den Berg I, Savenije MHF, Teunissen FR, van de Pol SMG, Rasing MJA, van Melick HHE, Brink WM, de Boer JCJ, van den Berg CAT, van der Voort van Zyp JRN, Deep learning for automated contouring of neurovascular structures on magnetic resonance imaging for prostate cancer patients, Physics and Imaging in Radiation Oncology. 2023; 26:100453. Lessons from 1,020 online adaptive radiotherapy sessions of vulvar carcinoma: From 66 to 90% rate of adaptation Malene Eppler Dam, Nikolaj Jensen, Trine Jakobi Nøttrup, Ivan Richter Vogelius Oncology, Rigshospitalet, Copenhagen, Denmark Purpose/Objective: Postoperative radiotherapy for vulvar carcinoma is challenging due to anatomical changesbeing common. Online adaptive radiotherapy is now the departmental standard for this treatment. We report on the clinical experience of >1,000 adaptive fractions for this rare disease.Specifically, we focus on adaption rates from initialphysician-driven to current RTT-drivenworkflow. Material/Methods: 54 patients with vulvar carcinoma were treated postoperatively using the online adaptive workflow on a ring-gantry accelerator (Ethos, Varian). Online adaptive treatment for this patient group was initiated inJanuary 2021 (Period A). In August 2023 the Hypersight upgrade including imager panel was installed (Period B).In Digital Poster Highlight 1333
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