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Radiation Planning Assistant - A Streamlined, Fully Automated Radiotherapy Treatment Planning System
Published on: April 11, 2018
Commissioning and verification of a 3D Monte Carlo independent calculation software for O-ring linac systems
Xiangyin Meng1, Tingting Dong1, Yongguang Liang1
1Department of Radiation Oncology, Peking Union Medical College Hospital, Beijing, China.
Background:
O-ring linac systems improve radiotherapy efficiency but require rigorous pretreatment verification due to increased delivery uncertainty in IMRT/VMAT. Existing methods face limitations: measurement-based approaches incur setup errors, while calculation-based methods (e.g., Monte Carlo) need machine-specific validation per AAPM TG-219.
Purpose:
To commission the O-ring linac model in RadCalc Monte Carlo software and establish its clinical dosimetric accuracy.
Methods:
The additional radiation to light field offset (ARLFO) parameter in RadCalc was adjusted from -0.08 cm (-0.8 mm) to +0.08 cm (+0.8 mm) (nine sets). TG-119 and clinical benchmark cases were used to design IMRT/VMAT plans. Verification plans were measured experimentally, and all plans were imported into RadCalc for secondary dose calculation. Triangular gamma analysis (3%/2 mm) compared Monte Carlo-simulated, measured, and TPS-calculated doses. The optimal ARLFO was determined by weighted averaging of gamma pass rates. The model was validated on 10 clinical cases per site (head, thorax, abdomen, pelvis).
Results:
Commissioning identified the optimal ARLFO parameter as -0.02 cm (-0.02 mm). Under the gamma analysis criterion of 3%/2 mm, the comparison between TPS-calculated doses and Monte Carlo-calculated doses for 10 clinical plans across four anatomical sites yielded: 98.9% ± 0.8% (head and neck), 98.5% ± 0.8% (thorax), 99.6% ± 0.3% (abdomen), and 99.1% ± 0.5% (pelvis). For verification plans, the gamma pass rates between Monte Carlo-calculated doses and measured doses were 97.5% ± 2.8% (head and neck), 95.6% ± 2.8% (thorax), 96.3% ± 2.9% (abdomen), and 99.4% ± 0.5% (pelvis), while comparisons of Monte Carlo-calculated doses versus TPS-calculated doses reached 99.5% ± 0.8% (head and neck), 99.2% ± 1.0% (thorax), 99.5% ± 0.9% (abdomen), and 99.9% ± 0.2% (pelvis), demonstrating consistent dosimetric accuracy of the optimized model across all clinical sites.
Conclusion:
This study establishes a commissioning methodology to determine the optimal ARLFO value for RadCalc, enabling clinics to achieve reliable independent plan verification for O-ring linac.
