Evaluation of dose homogeneity in volumetric modulated arc therapy (VMAT): total body irradiation (TBI) using multiple uniformity indices

Purpose: Total body irradiation (TBI) requires a highly uniform dose distribution to ensure treatment efficacy while minimizing toxicity. With the increasing use of volumetric modulated arc therapy (VMAT) for TBI, robust evaluation of dose homogeneity is essential. This study aims to assess dose uniformity in VMAT-based TBI plans using multiple homogeneity indices and to examine their relationship with standard deviation (StDev) derived from the planning target volume (PTV_TBI_Eval). Methods: Twenty VMAT TBI treatment plans were retrospectively analyzed. Dose homogeneity within the PTV_TBI_Eval was evaluated using the difference between maximum and minimum dose (Dmax–Dmin), the ICRU 83 homogeneity index, and the Yoon homogeneity index. Standard deviation (StDev) of the voxel dose distribution was obtained from the treatment planning system. Dose parameters including D2%, D98%, D50%, Dmax, and Dmin were recorded. Comparative and correlation analyses were performed between StDev and the homogeneity indices. Results: All plans achieved clinically acceptable dose coverage; however, variations in dose homogeneity were observed. The ICRU 83 homogeneity index ranged from 0.105 to 0.165, with similar trends observed for the Yoon index. Variations in Dmax–Dmin further reflected dose inhomogeneity. StDev demonstrated greater sensitivity to overall dose variation, particularly in cases with low-dose regions. A positive correlation was observed between StDev and both homogeneity indices. Conclusion: VMAT-based TBI plans achieved acceptable homogeneity; however, differences between evaluation metrics were evident. While conventional homogeneity indices provide practical DVH-based assessment, StDev offers a more comprehensive evaluation of dose distribution. The combined use of these metrics is recommended to enhance plan quality assessment in VMAT TBI.