Commissioning and Clinical Implementation of the First Monte Carlo (MC) Based Secondary MU Check System for IMRT
R Varadhan1*, S Way2, C Overbeck3, S Varadhan4, D Kristupaitis5, (1) Minneapolis Radiation Oncology, Minneapolis, MN, (2) Minneapolis Radiation Oncology, Robbinsdale, MN, (3) Minneapolis Radiation Oncology, Plymouth, MN, (4) Edina High School,(5) Minneapolis Radiation Oncology, Minneapolis, MN
Presentations
WE-C930-IePD-F4-4 (Wednesday, 7/13/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 4
Purpose: The use of robust and independent verification of IMRT/VMAT plans to verify Dose/MU delivered to the patient has been the mainstay of radiation oncology quality assurance. We describe the first Monte Carlo (MC) calculation based secondary MU check system.
Methods: An independent Monte Carlo patient transport code (SciMoCa) that was benchmarked against EGSnrc but with simplified beam properties and variance reduction techniques was integrated into MIM software. Beam modeling was performed and compared to measured data akin to TPS commissioning. Measured output factors, depth doses and beam profiles were compared to MC simulated values. Commissioning and clinical validation was performed according AAPM TG-219 recommendations
Results: Dose calculation in homogeneous phantom for various benchmark points as suggested in TG-219 report yielded 2% accuracy between measured, TPS MC calculated and SciMoCa MC calculated doses. In SBRT lung VMAT plans studied, the MC calculated doses between Monaco TPS and SciMoCa show agreement within 3% and a gamma pass rate of > 95% using 3%/3mm tolerance and 10% threshold. The dose calculated by collapsed cone (CC) convolution algorithm typically overestimated the dose to the center of lung PTV by 3%. DVH metrics agreed far better when comparing the MC calculated doses between TPS and SciMoCa when compared with CC convolution. Further in high Z materials, at the vicinity of both upstream and downstream metal interfaces, SciMoCa shows 3% agreement with TPS calculated MC dose in contrast to CC convolution algorithms where errors are in the range of 10-15%.
Conclusion: We have clinically implemented the first ever MC calculation based secondary MU check that exhibits calculation accuracy comparable to MC calculated dose by TPS and superior to currently commercially available 2D and 3D convolution/superposition based approaches. The integration of workflows that automatically calculate 3D local and global gamma maps greatly facilitate patient specific analysis.
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