S1895
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
adaptive radiotherapy, offering an opportunity to reduce imaging dose. Pseudo-computed tomography images generated using MRCAT enable MR-only external beam radiotherapy planning with MR. The combination of these techniques provides a zero- ionizing imaging dose option for radiotherapy. Previous studies have evaluated the dosimetry of MRCAT for clinical use in the pelvic region [1, 2]. However, its use for bone metastases and lymph targets remains unexplored. This study provides a dosimetric evaluation on CT- and MRCAT-based pelvic
radiotherapy plans. Material/Methods:
Six patients were included in this study: two with bone metastases and lymph targets, and four with lymph targets only. For each patient, a CT volume was acquired using a SOMATOM Confidence (Siemens Healthineers, Erlangen, Germany), and an MRCAT volume was generated using a Ingenia Ambition X (Philips Healthcare, Amsterdam, Netherlands) on the same day. The MRCAT volume was deformably registered to the CT volume using AccuContour 4.0.7.2 (Manteia Technologies Co., Fujian, China) to account for deformations between images. Reference plans were generated on the CT images based on clinical goals. These reference plans were then recalculated on the deformed MRCAT images. rED and structure doses for bone metastases and lymph targets were evaluated using Monaco version 6.2.2 (Elekta AB, Stockholm, Sweden) and 2-tailed paired t-tests. Plan and target VOI gamma analysis were performed using 3D Slicer version 5.8.1 (Surgical Planning Laboratory) [3]. Results: rED of targets differs significantly between CT and MRCAT images for both bone metastases and lymph targets (all p-values < 0.05 for the maximum, minimum, and mean rED of targets). However, the rED differences are small (e.g., CT: 1.14 vs. MRCAT: 1.15 for mean rED in bone metastases targets; CT: 0.97 vs. MRCAT: 0.98 for mean rED in lymph targets). The 3D gamma analysis suggests good overall plan and target VOI dose distribution similarity between CT- and MRCAT-based plans (gamma passing rates >95% (2%/2 mm)). Although DVHs show statistically significant differences between CT- and MRCAT-based plans, the dose differences are small—on average, the dose difference is less than 1.04%, and mostly less than 0.79% (e.g., CT: 104.80% vs. MRCAT: 104.37% for mean dose in bone metastases targets; CT: 102.89% vs. MRCAT: 102.58% for mean dose in lymph targets).
Conclusion: The dosimetric comparison between CT- and MRCAT- based plans demonstrates small differences in bone metastases and lymph targets, indicating that MRCAT is suitable for clinical planning for both targets. References: 1. Christiansen RL, Jensen HR, Brink C. Magnetic resonance only workflow and validation of dose calculations for radiotherapy of prostate cancer. Acta Oncologica, 56(6), 787-791, (2017).2. Tyagi N, Fontenla S, Zhang J, et al. Dosimetric and workflow evaluation of first commercial synthetic CT software for clinical use in pelvis. Phys Med Biol., 62(8), 2961-2975, (2017).3. Fedorov A., Beichel R., Kalpathy-Cramer J., Finet J., Fillion-Robin J-C., Pujol S., Bauer C., Jennings D., Fennessy F.M., Sonka M., Buatti J., Aylward S.R., Miller J.V., Pieper S., Kikinis R. 3D Slicer as an Image Computing Platform for the Quantitative Imaging Network. Magnetic Resonance Imaging. 2012 Nov;30(9):1323-41. PMID: 22770690. PMCID: PMC3466397. Keywords: MRCAT, pelvic radiotherapy plans, bone metastases DIAGNOSTIC CT-BASED SBRT FOR VERTEBRAL METASTASES: AN IN-SILICO PLANNING STUDY Jérôme Krayenbühl 1 , Indira Madani 1 , Léa Collet 2,3 , Stephanie Tanadini-Lang 1 , Matthias Guckenberger 1 1 Radiation Oncology, University Hospital Zurich, Zurich, Switzerland. 2 Physics, EPFL, Lausanne, Switzerland. 3 Physics, ETH, Zurich, Switzerland Purpose/Objective: To investigate the technical feasibility of using diagnostic CT (dCT) for treatment planning of SBRT for vertebral metastases. Digital Poster 2722
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