Purpose: The purpose of this study is to thoroughly validate electron Monte-Carlo (eMC) calculation algorithm from simple to complex custom-made phantoms that simulates real clinical cases and generate correction factors for independent hand calculations.
Methods: For five TrueBeam accelerators, beam modeling was performed for seven electron energies (6, 9, 12, 15, 18, 20, and 22 MeV) utilizing Eclipse treatment planning system. First part of the study validated the eMC dose calculation algorithm in the planning system by following AAPM Medical Physics Practice Guidelines (MPPG) 5.a. tests 8.1, 8.2, and 8.3. The data collection includes point measurements with ion chamber and profile checks with ion chamber array. To test eMC calculation accuracy for challenging geometries, such as obliquity, irregular surface and heterogeneity corrections, various tests were set up to simulate real clinical scenarios utilizing homemade phantoms. The collected data for each scenario for these cases was compared with water tank measurements. Three correction factors were calculated, gantry obliquity factor (GOF), irregular surface factor (ISF), and heterogeneity correction factor (HCF) respectively. These factors were plugged in our MU hand calculation and compared with TPS MUs.
Results: : The results showed a good agreement between ion chamber measurements and Eclipse eMC calculations. The point measurements of all MPPG 5a. testes were under 5%, and profiles and PDDs were 97±2% (3% dose difference and 3mm DTA tolerance) for all electron energies. Three correction factors calculated as gantry obliquity (GOF, range 0.89-0.99), irregular surface (ISF, range 0.89-.95), and heterogeneity correction factor (HCF, range 0.88-0.97 respectively. After plugging these correction factors, an adequate agreement was found (<5%) for all clinical cases.
Conclusion: Our methodology provides a unique method to compare the hand calculation MUs with planning system. Treatment planning system with eMC model accuracy calculates the dose for complex cases with obliquity, irregularity and heterogeneity involved.