Commissioning of a reference beam model-based Monte Carlo dose calculation algorithm for cranial stereotactic radiosurgery

Abstract

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.