ESTRO 2023 - Abstract Book

S1391

Digital Posters

ESTRO 2023

Conclusion In light of the measurements performed, the diffusion sequence with EPI scheme is feasible in an adaptive MRgRT workflow considering acquisition with 10 averages and 4 b-values. The fact remains that the calculated ADC values seem to underestimate those obtained with higher-field scanners.

PO-1683 Accuracy of dose calculation using a novel high-performance cone-beam CT imager

M. Bogowicz 1 , V. Trier Taasti 1 , G. Fonseca 1 , D. Lustermans 1 , C. Hazelaar 1 , H. Hansen 1 , F. Vaassen 1 , R. Canters 1 , W. van Elmpt 1 1 Department of Radiation Oncology (MAASTRO), GROW – School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, The Netherlands Purpose or Objective Cone-beam CT (CBCT) imaging has always been hampered by lower image quality than fan-beam CT. Furthermore, dose calculation based on CBCT scans has been less precise. In this work we evaluated the dose calculation accuracy for a novel CBCT system integrated in a standard linear accelerator. Materials and Methods A pre-clinical release of a high-performance CBCT imager (HyperSight™) integrated in a Halcyon (v4.0, Varian Medical Systems) treatment machine was evaluated for dose calculation purpose. This system incorporates a high-power kV source combined with a novel large flat panel detector (86x43 cm2) and software for CBCT iterative reconstruction with advanced scatter corrections (Acuros® CTS and Monte-Carlo based hardware scatter model) and metal artifact reduction (MAR). A CBCT-to-mass density calibration was performed (Gammex Advanced Electron Density Phantom, Sun Nuclear). For a comprehensive dose comparison, phantoms for 3 different body sites were used: head-and-neck (CIRS Proton Therapy Dosimetry Head, Sun Nuclear), thorax (Alderson RANDO, RSD Radiology Support Devices) and abdomen (CIRS Triple Modality 3D Abdominal Phantom, Sun Nuclear). In total 6 plans were created (Fig. 1). The plans encompassed a wide range of target locations and plan complexities. Targets and organs-at-risk (OARs) were defined on the planning CT images (SOMATOM Confidence, Siemens). Treatment plans were optimized and calculated in Eclipse™ (Acuros v17). CT and CBCT scans were rigidly registered, contours were copied and plans were re-calculated with fixed monitor units on the CBCT scan. Differences in Dmean to relevant target volumes and OARs were evaluated and gamma analysis was performed (3%/1 mm and 2%/1 mm, dose normalized to prescription dose, 20% dose threshold).