ESTRO 2025 - Abstract Book

S3599

Physics - Quality assurance and auditing

ESTRO 2025

Results: SciMoCa provides a very accurate secondary dose calculation that can identify dose calculation errors much smaller than 1 % [3]. For example, SciMoCa has found a strong correlation between PTV mean dose deviation (primary/secondary dose calculation) and MLCLO for multiple treatment sites (Figure 1), likely caused by a too simple modeling of the MLC leaf tip in Eclipse 16.5. Log file analysis can easily identify planned/actual 2D fluence deviations of 1 % due to MLC and MU deviations. However, no correlation has been found between 2D fluence deviations and PCMs over a period of 5 years (examples in Figure 2). Thus, all observed 2D fluence deviations are caused by accelerator technical faults. For example, a single TrueBeam MLC fault in 2019 caused fluence deviations >2 % for >10 % of the field area for 65 fields, which went undetected by Varian TrueBeam.