SU-E-T-461: Validation of Planning Algorithms in Dynamic Conformal Arc in IPlan Using ArcCHECK and 3DVH

Authors


Abstract

Purpose:

To study the effect of limited angular resolution of pencil beam calculation (PBC) on dynamic conformal arc plan (DCAP) in iPlan (BrainLab) using the ArcCHECK sytem and 3DVH software (Sun Nuclear Corporation).

Methods:

Four DCAPs were generated in iPlan RT Dose 4.5 treatment planning system on the ArcCHECK cylindrical phantom with central planning target volume (PTV). A cylindrical shell structure (SHELL) 2.85cm from phantom surface and 1.5 mm thickness was created to simulate the ArcCHECK diode array. Planned doses were calculated using both Monte Carlo calculation (MCC) and PBC algorithms, and exported to 3DVH software for global and target based comparisons using the 3Dgamma index. Four additional DCAPs were created and calculated on patient CT images and mapped onto the ArcCHECK phantom for measurement using a Varian TrueBeam STx. The measurements were compared against both MC and PB calculation using gamma index analysis.

Results:

For the ArcCHECK phantom, the dose distribution agreement quantified with 3D-gamma index is better (average-gamma (<γ>)=99.9%vs.79.1% and 96.8%vs45.7%, p=0.0294, 0.0286 for gamma (2mm,2%) and (1mm,1%) criteria respectively using Mann-Whitney U test) in the PTV than in the SHELL. The measurements show better agreement with MCC than the PB (<γ>=100%vs.86.7%, 99.6%vs.72.3%, 85.5%vs.50.8%, p=0.021, 0.026, 0.029 for gamma (3mm,3%), (2mm,2%) and (1mm,1%) criteria using Mann-Whitney U test respectively). The effect due to limited (10 degree) angular resolution of the PBC was observed, and it can be one of the possible reasons for poor agreement between measurement and PB calculation.

Conclusion:

The PBC of iPlan shows poor peripheral dose calculation accuracy for dynamic conformal arc plans due to limited angular resolution, but it performs well in the area close to target volume without considering heterogeneity. Since the user cannot change the 10 degree angular resolution of PBC, MCC is more appropriate for dynamic conformal arc plans.

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