Dose calculation errors for volumetric modulated arc therapy plans of various complexity

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• Volumetric Modulated Arc Therapy (VMAT) plans often feature complex beam apertures, challenging accurate dose calculations.
• Assessing dose calculation accuracy is crucial for ensuring effective and safe radiotherapy.

Purpose of the Study:

• To investigate potential dose calculation errors in VMAT plans across varying complexity levels.
• To compare the performance of six different dose calculation methods for VMAT.

Main Methods:

• Sixty VMAT plans from twenty patient cases with differing complexities were analyzed.
• Six distinct dose calculation algorithms were employed for each plan.
• Three-dimensional dose distributions were evaluated using voxel-wise standard deviations (2SDs), focusing on 2SDMean and 2SD2cc metrics.

Main Results:

• Higher dose calculation variations (2SD values) were observed outside the planning target volume (PTV), particularly in low-dose and buildup regions.
• Average 2SDMean/2SD2cc values within the PTV were 0.9-1.2%/1.8-5.1%, increasing to 1.8-3.1%/8.4-18.7% in regions 1 cm outside the PTV.
• Organs at risk showed larger variations than PTVs, with up to 5%/15% differences noted for prostate cases.

Conclusions:

• Dose calculation method variations were more pronounced in organs of interest compared to PTVs.
• Patient-specific case differences in dose calculation variability exceeded differences attributed to plan complexity levels.