ESTRO 2024 - Abstract Book

S3432

Physics - Dose calculation algorithms

ESTRO 2024

Figure 1. Dose(%) vs. size field(cm). Crossline dose profile of a square field 10cmx10cm at 30cm depth compared with a same dose profile obtained from the TPS calculated with Acuros XB (v.15.6.06)

As for the comparisons between measurements on Ethos and Halcyon units (HAL1 and HAL2) a very good agreement was found and all results are above 90% for the 1%/1mm gamma criteria in all analyzed dose profiles and PDDs (Table 1). The calculation algorithms implemented in Eclipse for Ethos and Halcyon treatment units are pre-configured by Varian, without providing the user the ability to make changes to them. Varian reported that these discrepancies (Table 1) could be due to the mismatch between the spot size of the target configured on the dose calculation algorithm and the actual one on the treatment unit. The spot size of algorithm v.15.6.06 is preconfigured at 0 mm size and has been corrected in later versions of the algorithm by changing this value to 0.7mm in both directions in version 17 and to 1.2mm in x direction and 1.5mm in y direction in version 18. Dose profiles from a test Ethos unit configured with Acuros XB version 18 were obtained. The comparison with the measurements shows an improvement (concretely, 4-9 % of the 1%/1mm gamma criteria), so the concordance is greater than using a 0mm target spot size. It should be pointed out that in the commissioning of the two Halcyon treatment units, the same tests were conducted comparing the measurements against calculations in Eclipse using the AAA v.13.6 calculation algorithm, and the gamma criteria 1%/1mm yielded values exceeding 90% in all cases, indicating a very good agreement between measurements and AAA v.13.6 calculations.