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Impact of Volumetric Modulated Arc Therapy Control Point Discretisation on Dosimetry: A Comparative Evaluation of Two
Sankar Arumugam1,2, Tony Young1,3
1Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, New South Wales, Australia.
Aim:
The aim of the study was to investigate the dose calculation accuracy of volumetric modulated arc therapy (VMAT) control point (CP) discretisation approaches in Pinnacle and RayStation treatment planning systems (TPSs).
Methods:
The 6MV beam model for Elekta linear accelerator with Agility head generated in Pinnacle and RayStation was used in this study. The impact of CP discretization on dose calculation was assessed using 10 prostate and ten breast VMAT plans generated in each TPS. In Pinnacle, VMAT plans were generated using both 4° and 2° CP gantry spacing, while RayStation plans used 2° spacing. To assess the dosimetric differences due to CP discretization, VMAT plans from Pinnacle were recalculated in RayStation, and vice versa. The impact of CP discretization on target volume and critical structures was assessed by comparing dose volume histogram metrics. The agreement between ArcCheck-measured and TPS-calculated doses was assessed using gamma analysis with a 2%2 mm tolerance criterion.
Results:
The prostate and breast plans with 2° spacing generated in Pinnacle and recalculated in RayStation showed a mean (Std Dev) target dose agreement of 1.0 (0.4)% and 0.3 (0.8)%, respectively. The similar comparison for RayStation-generated plans recalculated in Pinnacle was 0.8 (0.2)% and 2.4 (0.2)%, respectively. The ArcCheck measurements of Pinnacle-generated prostate and breast plans showed a mean gamma pass rate of 96.5 (1.2)% and 91.5 (5.2)%, respectively. Similarly, RayStation-generated prostate and breast plans had a mean gamma pass rate of 96.7 (2.3)% and 95.4 (3.7)%, respectively.
Conclusions:
The CP discretization approach implemented in RayStation results in improved dose calculation accuracy of VMAT plans, particularly for plans with larger CP spacing.
