S2403
Physics - Quality assurance and auditing
ESTRO 2026
Anderson, J. M. Moran and M. M. Matuszak, “Predicting deliverability of volumetric-modulated arc therapy (VMAT) plans using aperture complexity analysis,” Journal of applied clinical medical physics, vol. 17, no. 4, pp. 124-131, 2016. [2] K. C. Younge, M. M. Matuszak, J. M. Moran, D. L. McShan, A. B. Fraass and D. A. Roberts, “Penalization of aperture complexity in inversely planned volumetric modulated arc therapy,” Medical Physics, vol. 39, no. 11, pp. 7160 - 7170, 2012. Keywords: SABR, QA, Modulation Complexity Scoring Digital Poster 4622 A Multi-Centre Comparison of CBCT-derived DVHs- of-the-Day Sarah OS Osman 1,2 , Mohammad Hussein 3 , Adeyemi Akintonde 4 , Catharine H Clark 1,4 , Jamie R McClelland 4 1 Department of Radiotherapy Physics, University College London Hospitals NHS Foundation Trust, London, United Kingdom. 2 National RTQA, Radiotherapy Trials Quality Assurance (RTTQA) Group, London, United Kingdom. 3 Radiotherapy and Radiation Dosimetry Group, National Physical Laboratory, London, United Kingdom. 4 UCL Hawkes Institute, Department of Medical Physics and Bioengineering, University College London, London, United Kingdom Purpose/Objective: The ability to accurately calculate DVHs-of-the-day from daily CBCT scans is key for enabling adaptive RT.
average M PCM score. The ROC analysis determined a suitable threshold of 0.18 mm-1 for predicting PTQC results for SABR spine plans with true positive and false positive rates of 72% and 18%, respectively.
As shown in Figure 2, significant reductions in M PCM scores were exhibited by variant plans that received complexity constraints, and plans that did not receive constraint possessed greater M PCM scores. Calculated target and spinal cord/cauda equina dose differences correlated well with measured target and organ dose differences. Both calculated and measured dose differences suggest that plans optimised to possess lower M PCM scores exhibited smaller target and OAR dose differences, whereas plans produced without constraint exhibited larger dose differences.
This requires both synthetic CTs and updated structures derived from the CBCT scans. We
developed a rigorous methodology for validating DVH- of-the-day results and applied this in a multi-centre study of head and neck (H&N) RT patients. Material/Methods: Datasets from 50 oropharyngeal cancer patients who underwent re-planning during their treatment were collected from five RT centres. Each dataset included the original planning CT (pCT) and structure set (pStruct), the re-scan CT (rCT) and structures re- outlined on this (rStruct), and the CBCT nearest in time to rCT. Ten representative patients were selected based on setup variability and anatomical changes commonly observed in H&N patients. VMAT plans were generated centrally in Raystation to the same clinical prescription and goals. The pCTs, pStructs, and CBCTs were distributed to participating centres, four of whom returned synthetic CTs (sCT) and updated structures (uStruct) generated using their institutional DIR protocols. Independently, investigators generated additional sCTs and uStructs using the open-source tool NiftyReg to provide a fifth comparison (Centre 5).Ground-truth CTs (gCT) and structures (gStruct) were generated using DIR (NiftyReg) to better align the rCT to the CBCT. DVHs-of-the-day were calculated
Conclusion: M PCM scores provided a robust model for predicting QC results for SBRT spine plans. This model is in clinical use to inform the optimisation process and improve treatment plan quality and accuracy. References: [1] K. C. Younge, D. Roberts, L. A. Janes, C.
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