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Session: CBCT-guided Adaptive Radiotherapy [Return to Session]

Clinical Experience with a CBCT Dose Reconstruction Process to Inform Adaptive Radiotherapy for Head and Neck Cancer Patients

A McNiven1,2,3*, B Chan1, J Moseley1, V Kong1,2, A Shessel1, J Bissonnette1,2,3,4, M Velec1,2, J Waldron1,2, A Hope1,2, T Patel3, T Tadic1,2,3, (1) Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, CA (2) Department of Radiation Oncology, University of Toronto, Toronto, ON, CA (3) Techna Institute, University Health Netowrk, Toronto, ON, CA (4) Department of Medical Biophysics, University of Toronto, Toronto, ON, CA


TU-D1000-IePD-F2-4 (Tuesday, 7/12/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 2

Purpose: To evaluate an off-line adaptive radiotherapy workflow for head and neck (HN) cancers that relies on a formalized dose reconstruction process (Dose-of-the-Day (DOTD)) on cone-beam computed tomography (CBCT) images.

Methods: DOTD, a semi-automated process, was implemented for routine off-line re-planning assessment for HN patients. The process includes physics quality control (QC) and multi-disciplinary consultation to evaluate the need for adaptation. Case details, clinical decisions, reasons triggering DOTD, process timing and any QC failures are tracked prospectively for quality improvement purposes.

Results: Results are reported for the first 103 HN DOTD assessments (97 patients). This corresponds to 6-8% of total HN patients during that time. Average time for CBCT data transfer, registration and dose reconstruction was approximately 15 minutes (excluding QC and review time). The top three reasons for performing DOTD were: soft tissue increase (edema or progression) and positioning errors in lower neck or the tongue. These reasons accounted for 56% of the DOTD activities. After DOTD, 69% of the cases continued with no intervention, and a re-plan was completed for 18%. The remaining 13% required further assessment (e.g. re-CT sim or a subsequent DOTD activity) or had patient-specific IGRT instructions updated based on DOTD findings. In 46 cases an initial decision was documented prior to DOTD (image review only), and DOTD changed the decision in 16 cases. This eliminated unnecessary repeat-simulations in three cases, but also identified three re-plans that otherwise would have been missed. There has been no measurable increase in re-planning rates.

Conclusion: Dose reconstruction has been successfully implemented clinically as an important tool for guiding decisions about adaptive RT. Further work is ongoing to provide more quantitative measures to predict the need for re-plan and to better understand long-term changes in practice due to the addition of delivered dose estimates during offline image review.


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