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A CT-Based On-Line Radiotherapy Treatment for Urgent Treatment Delivery

M Held

M Held*, O Morin, J Pouliot, University of California San Francisco, San Francisco, CA

SU-E-J-180 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To implement a new CT-based on-line radiotherapy treatment workflow (CTORT) to rapidly simulate, plan and deliver emergency radiation treatments (ERTs), while the patients are on the treatment couch. Our specific objective was to treat in under 15 minutes with dose calculation accuracy better than 5%. A key component was to investigate the effect of cone-beam CT (CBCT) image quality on dose calculation accuracy.

Methods: Artificial and clinical megavoltage and kilovoltage CBCT phantom and patient images were used for simulation and dose calculation. Electron density-to-Hounsfield unit (HU) calibrations were acquired for the CBCT systems and integrated in the planning system. A specialized treatment planning interface (ERT module - Prowess) was developed to streamline the dose prediction process. Image degradations (noise, reduced contrast, scatter artifact, non-uniformity, etc.) observed on CBCT images were applied to CT images to quantify the respective reduction in dose calculation accuracy. Dose distribution comparisons provide a direct method to predict achievable dose calculation accuracy of specific clinical sites using MV and kV CBCT images. The complete workflow was tested off-line on an array of emergency and palliative radiotherapy cases.

Results: A MVCBCT specific electron density calibration allows for dose calculation accuracy better than 5% for all cases in presence of heterogeneity. Based on digital phantom analysis, CBCT non-uniformity is the biggest contributor to reduction in dose calculation accuracy. The complete workflow was tested on simple cases to show simulation, planning and treatment delivery performed within 15 minutes.

Conclusion: CBCT image quality is satisfying for simple dose calculation as used for urgent radiotherapy. CTORT presents a workflow of imaging, dose planning, treatment delivery and quality assurance that allows for fast radiotherapy. This approach may reduce patient pain, improve dose planning and delivery accuracy and provide new possibilities for simple radiotherapy treatments when CT simulation is not feasible.

Funding Support, Disclosures, and Conflict of Interest: Siemens OCS; Prowess Inc.

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