Commissioning and performance evaluations of the electron Monte Carlo algorithm in a new commercial treatment...

This study provides a comprehensive evaluation of the newly implemented electron Monte Carlo dose calculation algorithm in the commercial treatment planning system, uTPS. It investigates the performance of the algorithm by examining its dosimetric accuracy and calculation speed, which have not been previously reported in the literature.

To evaluate the dose calculation accuracy of the electron Monte Carlo algorithm in uTPS, the beam data from the electron energies of 6 MeV, 9 MeV, and 12 MeV in the newly developed dual-layer MLC CT-linac were modeled. Following AAPM MPPG 5.b, the calculated point/plane doses under normal and extended SSD, oblique incidence and cutouts, and heterogeneous phantoms with different energies were compared with the corresponding measurement data. The calculation time was evaluated by the comparisons between two different calculation workstations.

The beam data of 6 MeV, 9 MeV, and 12 MeV are well reproduced by the calculations. A dose grid resolution of 2 mm, 1% uncertainty, and dose to medium mode were used. Calculations successfully validated against the measured beam data, achieving mean dose differences of less than 2% in a water tank. The gamma passing rates were generally high and mostly exceeded 95% using 3 mm/3% criteria, although several larger-field, extended-SSD, and oblique/cutout cases showed lower passing rates, with minimum values remaining above 90%. The cutout tests, both special designed and patient specific, demonstrate that the algorithm can handle cases with cutouts effectively. In the heterogeneous phantom tests, the point dose differences for all SSDs are within 3.3%, indicating the accuracy of the uTPS Monte Carlo algorithm in handling heterogeneous media. The calculation times ranged from approximately 5 - 30 s for a statistical uncertainty of 1%, whereas achieving a tighter uncertainty of 0.5% increased the computation time to between 10 s and 2.5 min.

Verifications performed under these basic and complicated conditions indicate that the accuracy of electron Monte Carlo algorithm in uTPS meets the requirements of MPPG 5.b for electron beam dose verification. The electron Monte Carlo algorithm of uTPS demonstrates accuracy comparable to that of other commercial TPSs. The comprehensive evaluation confirms the algorithm's robust performance, as it achieves the necessary levels of dosimetric precision and calculation times to support diverse radiotherapy workflows.