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Implementation of a Simplified Analytical Random Walk Model for Clinical Scenario in Proton Treatment

W Yao

W Yao*, J Farr , V Moskvin , L Zhao , R Lukose , C Hua , D Sobczak , P Tsiamas , M Axente , T Merchant , St. Jude Children's Research Hospital, Memphis, TN


MO-L-GePD-TT-5 (Monday, July 31, 2017) 1:15 PM - 1:45 PM Room: Therapy ePoster Theater

Purpose: To implement our simplified analytical random walk model (SaRWM) proton dose calculation algorithm for clinical use and examine its accuracy.

Methods: Recently, we proposed SaRWM for proton dose calculation without the nuclear interaction component. SaRWM gives an analytical solution of the proton dose by treating each medium voxel as a proton source. It was verified by TOPAS Monte Carlo simulation. In this work, we included the nuclear interactions into the previous SaRWM, and implemented SaRWM with the measured proton range, beam divergence, spot size for our proton pencil beam scanning facility. The proton fluence in SaRWM was calibrated to our machine Monitor unit (MU). The accuracy of SaRWM was evaluated by the measured integral dose of each energy in water, point dose from a spread-out Bragg peak (SOBP, in depth from 10 cm to 20 cm) plan in water, and gamma test of the 3D dose distribution in patient QA plans against MatriXX measurement.

Results: The range for each energy was calibrated within the measurement uncertainty (0.4 mm) from the measurement. The point dose difference was 1.7% at 10 cm and 0.65% at 20 cm (the point dose at 15 cm was used in the MU calibration). For examined total 18 fields of patient plans, the gamma test (3%/3mm with 10% threshold dose) pass rate was 93.8%±3.2% at depth 4 cm (the shortest proton range was 3.881 cm in our facility), 98.2%±1.8% at depth 6 cm and 99.5%±0.5% at depth deeper than 7 cm. The dose halo in lateral from SaRWM was well calculated. For typical patient plans, it took SaRWM 20 to 40 minutes per beam per CPU for the dose distribution with resolution 1x1x1 mm3. Approximately 75% of calculation time was for the nuclear interaction.

Conclusion: Our SaRWM has been successfully implemented for our proton facility.

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