ESTRO 2024 - Abstract Book

S4927

Physics - Quality assurance and auditing

ESTRO 2024

2. Systematicity of deviations: to assess the systematicity of the two major source of errors the correlations between the deviations calculated for the first fraction and for all subsequent fractions in the treatment series using Pearson correlation coefficient was analyzed. The analysis was performed for all patient cases.

Results:

1. Dosimetric impact of deviations. The highest impact on gamma pass rate (PR) was observed for spot and couch position deviations, whereas deviations in spot MU and gantry angle have only minor impact. (Fig. 1). Median gamma PR (1%/1mm) shows a significant increase (12.57 percentage points (p.p.) and 4.78 p.p. for spot and couch position respectively) for doses calculated for treatment plans compared to single fields. However, this increase is not significant for plans combined into treatment series (1.41 p.p and 1.17 p.p. for spot and couch position respectively).

Figure 1. (A) Voxel-wise dose difference histograms between recalculated dose distribution from delivery log-files and nominal dose distribution, for one selected patient case. Blue line indicates the difference for one selected field, orange line indicate difference for treatment plan including multiple fields.B) Gamma pass rate (1%/1mm) between