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Implementation of Clinical Monte Carlo Dose Calculation for CyberKnife On a Web-Based Treatment Planning System WebTPS

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K Zerouali

K Zerouali1*, M Renaud2, F DeBlois2, H Bouchard3, J Carrier3, (1) Universite de Montreal, Montreal, Quebec, (2) McGill University, Montreal, Quebec, (3) Centre universitaire de l'Universite de Montreal, Montreal, Quebec

SU-E-T-498 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The scope of this study is to implement an accurate Cyberknife model on a web-based tool (WebTPS), which uses the EGSnrc Monte Carlo dose calculation engine. WebTPS will be mostly used as a reference to evaluate clinical treatment plans in highly heterogeneous phantoms.

Methods: The WebTPS dose calculation module is linked to the user code DOSxyznrc. WebTPS automatically converts CyberKnife clinical plans to DOSxyznrc input files. Phantoms are created using a tissue segmentation method from HU-ED calibrated curves and materials are assigned based on CT data and contours performed by radiation oncologists. Parallel computation is run on a high-performance cluster (Compute Canada) to achieve reasonable simulation time. The CyberKnife model is built on the BEAMnrc system using manufacturer's specifications. Simulated and experimental data are compared to estimate the optimal electron beam parameters. The beam energy estimation is based on percent depth dose (PDD) data comparison, while the spot size is validated using output factor (OF) and off-axis ratio (OAR) data. An egs_chamber model of a PTW60012 diode is used to simulate OF experimental measurements for different collimator sizes.

Results: A preliminary linac model optimization yields a 0.5% agreement between experimental and simulation PDD data; a 0.5% or 1 mm agreement for OAR data and a 2% agreement for OF data. Full treatment plan simulations are achieved with the CyberKnife model using patient heterogeneous phantoms. Uncertainties under 1% are achieved for less than 2 hours of CPU time.

Conclusion: This work aims to develop a suitable model for reference plan dose calculation. WebTPS will be used in several clinical and research applications where the CyberKnife embedded ray-tracing algorithm show significant limitations. Further improvements are yet to be achieved to match experimental data to a level of 1%.

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