Rapid commissioning of Brainlab Elements for SRS: end-to-end evaluation of Monte Carlo and pencil beam algorithm across homogeneous and heterogeneous phantom environments.

PURPOSE: Brainlab released a reference beam model that accelerates Brainlab Elements treatment planning system (TPS) commissioning process for stereotactic radiosurgery (SRS) using an Elekta Versa HD linear accelerator. A series of end-to-end (E2E) phantom studies were performed to evaluate the Monte Carlo (MC) and pencil beam (PB) dose calculation algorithms using the reference beam model released by Brainlab with Elements v4.0 and v4.5. METHODS: A reduced set of water tank measurements of percent depth dose (PDD), beam profiles, multileaf collimator (MLC) gap, and output factors were taken using a PTW 0.125-cc Semiflex ionization chamber, PTW Si-diode, and PTW Microdiamond chamber for field sizes including 6 × 6, 10 × 10, 30 × 30, and 100 × 100 mm2 using 6MV and 6MV flattening filter-free (FFF) beams. MPPG 5.b testing was performed after commissioning to validate TPS performance. A set of RTsafe cranial and spine phantoms and an Exradin A16 ionization chamber was used for E2E testing. The cranial phantom was used to evaluate single target and dynamic conformal arc therapy (DCAT) cranial planning, and spine phantom filled with water, air, and air with a steel rod insert was used to evaluate spine SRS planning. MC and PB (v4.0 and v4.5) dose calculation algorithms in Brainlab Elements were used to evaluate the planning modules across all phantom environments. RESULTS: All commissioning validation tests satisfied the MPPG 5.b tolerance criteria. The commissioning process took a qualified medical physicist (QMP) and a medical physics resident 1 day to complete. MC dose calculation (2%/1 mm) demonstrated clinically acceptable agreement within 3% of measured dose for E2E tests. In-field PB calculations were within 5%. PB calculated plans showed some improvement with measured values when upgrading the beam model from v4.0 to v4.5. CONCLUSION: The reference beam model provided an efficient framework for commissioning the Brainlab Elements TPS. Brainlab Elements' MC dose calculation algorithm provides reliable accuracy across clinically relevant heterogenous and small field conditions.