ESTRO 2024 - Abstract Book

S4853

Physics - Quality assurance and auditing

ESTRO 2024

error was simulated by shifting all the spot positions uniformly by 2mm in various directions. Gamma Passing Rate (GPR) is used to assess the dose perturbations compared to the nominal plans.

Results:

For random error with GD of PE of 1mm, both SPArc and IMPT are comparable with a GPR exceeding 95%. However, SPArc could provide better GPR in the presence of 2mm PE with GD (Figure 1). For system error of 1mm, SPArc and IMPT maintained the feasible GPR of over 99%. As the criterion is stricter to 1%/1mm?, SPArc provides much better GPR compared to IMPT. As PE of 2mm, SPArc also shows much better GPR. More specifically, SPArc could provide (99.40±0.74)%, (93.66±4.75)% and (61.53±10.30)% of GPR for 3mm/3%, 2mm/2%, and 1mm/1% criteria in comparison with IMPT . In the brain case, SPArc could provide smaller dose difference for the brainstem (maximum dose: 2.12% vs 5.71%) and left cochlea (mean dose: 4.26% vs 12.80%) compared to IMPT (table1) with similar differences for other OARs.

Figure 1. A representative comparison between IMPT and SPArc in the presence of spot position error in a brain case.

Table 1. Dosimetric comparison

Dosemetric parameter

IMPT

SPArc

ΔDmax_CTV/Dmax_CTV (%)

0.69%

0.00%

ΔTarget Coverage/Target Coverage (%)

3.94%

4.22%

ΔDmax_Brainstem/Dmax_Brainstem (%)

5.71%

2.12%

ΔDmean_Cochlea_R/Dmean_Cochlea_R (%)

1.69%

3.58%