Empirical model for a three-dimensional dose verification system and its application in volumetric-modulated arc therapy for heterogeneous and long-target tumors

Purpose: To perform commissioning of the VMAT dose verification system 3DVH from a unique perspective and investigating its clinical applications in unreported cases with heterogeneous organs or long-target tumors. Methods: Initially, the standard ArcCheck calibration process was conducted. Then, the impact of absolute dose calibration values and ArcCheck CT density settings on the accuracy of the 3DVH reconstruction model was assessed. Subsequently, ten lung cancer cases with heterogeneous organ-encased targets and ten cervical cancer cases with large target volumes were selected to receive VMAT treatment with a TrueBeam Linac. Finally, the performance of the 3DVH method in such radiotherapy validations was assessed. Results: Various calibration files had distinct impacts on ArcCheck 2D surface dosimetry and 3DVH dose reconstruction, thus requiring separate optimal calibrations files for these two purposes. The 3DVH dose reconstruction mode exhibited the highest accuracy when using the optimal ArcCheck density value of 1.1787 g/cm³ and an absolute dose calibration value of 249.96 cGy. In all test cases, deviations for target Dmean and D95% were within ±4.2% compared to the planned dose, with notable variations in critical organ doses. In structure-based 3D gamma evaluation, differences were observed compared to existing reports. Conclusions: It's crucial to account for the ArcCheck array calibration and the interplay between CT density settings and absolute dose calibration values to identify the best combination for an optimal 3DVH dose reconstruction model. The performance of 3DVH in verifying VMAT doses for tumors in heterogeneous or longer target areas may exhibit slight variations compared to other regions.