The BeamSplitter – An algorithm providing the dose per control point of radiation therapy treatment plans

Purpose

Commercial radiation therapy treatment planning systems (TPS) provide the three-dimensional time-integrated planned dose distribution. A four-dimensional (4D) dose calculation is essential to minimise dose-rate effects on pacemaker or in total body irradiation treatment or for time-dependent patient-specific quality assurance. We introduce the BeamSplitter, an algorithm in a commercial TPS generating 4D dose calculation.

Methods

Automation was performed with the Eclipse Scripting Application Programming Interface (ESAPI, v16, Varian Medical System). The accumulated and reference dose distributions of twenty-one patients treated in 2022 at our institution were compared. The patients were selected to cover a broad range of modulated delivery techniques and plan complexity, quantified with the average leaf pair opening (ALPO). The dose distributions were compared with gamma passing rates (γPR). Moreover, the mean absolute percentage error (MAPE) between accumulated and reference dose metrics (planning target volume (PTV) D99% / D95% in stereotactic / non-stereotactic treatment, organs at risk (OAR) D5cc / D0.03 cc, and mean dose) was calculated. Dose accumulation was validated by point dose measurement.

Results

The ALPO ranged from 11.6 mm to 77 mm. The accumulated and reference dose distributions were similar (${\gamma PR}_{0mm}^{1\%}$ > 90 % in all patients). The MAPE between reference and accumulated dose metrics was lower than 1 % in all cases. The average dose difference through time between the accumulated and measured dose was lower than our clinical tolerance of 3 %.

Conclusions

The BeamSplitter is the first validated algorithm generating a 4D dose calculation of radiation therapy treatment plans within a commercial TPS.