Commissioning of a reference beam model-based Monte Carlo dose calculation algorithm for cranial stereotactic
Yohan A Walter1, Anne N Hubbard2, Philip F Durham2
1Department of Radiation Oncology, Willis Knighton Cancer Center, 2600 Kings Highway Shreveport, LA 71103, USA; Department of Clinical Research, University of Jamestown, 4190 26th Avenue South Fargo, ND 58104, USA.
Purpose:
In treatment planning system (TPS) commissioning for stereotactic radiosurgery (SRS), the required measurements and precision necessary to generate an accurate beam model make the process taxing and time-consuming. Recently, Brainlab AG released reference beam models available for use with the Elements TPS. In this work, we detail our implementation of reference beam model-based Monte Carlo dose calculations for our Elements 4.0 TPS.
Methods:
Depth dose, output factor, and beam profile measurements were used to select a reference beam model. 9 treatment plans encompassing the range of clinical use cases were created. Patient QA measurements were performed using a high-resolution detector array. Dose distributions were mapped to the QA array using the reference beam model with 1-2 mm grid resolution. Independent MU verifications were performed for each test plan. An end-to-end test was performed for final verification of system performance and data integrity.
Results:
Acceptable agreement was demonstrated between measured data and the reference beam model. All QA gamma pass rates exceeded 95 %. Measured peak dose differences were over 5 % for targets with diameter <7 mm when using a 1.0 mm Monte Carlo grid resolution. 1 of the 46 tested arcs had over a 5 % difference between MU verification and the TPS-calculated MU. End-to-end testing verified system performance.
Conclusion:
Validation testing demonstrated good agreement between the reference beam dataset and machine performance for targets with diameters ≥7 mm. The use of a reference beam model may significantly reduce measurement burden while mitigating potential failure modes associated with TPS commissioning.
