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Performance Characterization of Kilovoltage Intrafraction Monitoring; a Novel Real-Time Tumor Localization Modality

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J Ng

J Ng1*, R O'Brien1, P Poulsen2, W Fledelius2, Z Kuncic1, P Keall1, (1) The University of Sydney, Sydney, Australia,(2) Aarhus University Hospital, Aarhus, Denmark

WE-A-134-6 Wednesday 8:00AM - 9:55AM Room: 134

Purpose: Kilovoltage Intrafraction Monitoring (KIM) is a novel real-time tumor localization modality. Previously, KIM was used to determine the prostate trajectories during treatment retrospectively. We have recently further developed KIM for real-time tumor localization. This study aims to characterize the performance of KIM in a real-time clinical environment as a necessary condition for a prospective clinical trial.

Methods: Intrafraction kilovoltage images acquired during Intensity Modulated Arc Therapy (IMAT) delivery from 9 prostate cancer patients (244 fractions) with implanted fiducial gold markers were used to simulate real-time acquisition with the real-time KIM software. The images were passed to the software in an exact replica of the clinical workflow. The software estimates the 3D positions in real-time from the 2D projection images by maximum likelihood estimation of a 3D probability density function. The root-mean-square-errors (RMSE) between the real-time and retrospective KIM data from a previous study were computed to evaluate the 3D position determination accuracy. The average processing time per image was computed to determine the real-time operability.

Results: For the 9 patient dataset, the RMSEs between real-time and retrospective KIM are: 0.98 mm (left-right), 0.35 mm (superior-inferior), 0.99 mm (anterior-posterior) and 1.49 mm (3D). The average processing time per image is 0.24 s.

Conclusion: The feasibility and accuracy of real-time KIM has been demonstrated. With additional quality assurance tests, this work enables a clinical trial of real-time KIM involving 30 prostate cancer patients, for which ethics approval has been sought.

Funding Support, Disclosures, and Conflict of Interest: Funding support was received from the Australian National Health and Medical Research Council Australia Fellowship and US National Institutes of Health/National Cancer Institute grant CI R01CA93626. Drs Keall and Poulsen are inventors of the kilovoltage intrafraction motion monitoring method investigated clinically in this study. Stanford University has filed a US patent application (no. 20100172469) and has licensed the method to Varian Medical Systems. No commercial support was received for this study. Conflict of interest: none.

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