Evaluation of the feasibility of log file-based three-dimensional independent dose verification system in quality assurance of intensity-modulated radiation therapy

Objective: To assess the feasibility of the log file-based three-dimensional independent dose verification system for the quality assurance of clinical radiotherapy. Methods: The statistical values of the percentage depth dose, off-axis curves and output factor calculated by the Mobius system were statistically compared with the measured data by three-dimensional water tank. The three-dimensional independent dose verification in clinical radiotherapy plan and the acceleratr log file-based three-dimensional dose verification during the treatment were performed in 17 patients with nasopharyngeal cancer. The accuracy of dose calculation and reconstruction of Mobius system was assessed. A statistical analysis was performed on the intra-fractional γ pass rate (3%/3mm) for each patient to evaluate the stability of intra-fractional radiotherapy. Results: The percentage depth dose, off-axis curve and output factor statistically calculated by the Mobius system matched well with the data measured by three-dimensional water tank. The dose-volume histogram (DVH) parameters between the target area and organ at risk during clinical radiotherapy plan were statistically compared in 17 patients with nasopharyngeal cancer. The maximum deviation was -2.16% for the three-dimensional independent dose verification in the clinical radiotherapy plan, and 0.18 Gy for the accelerator log file-based three-dimensional dose verification. The average γ pass rate for 17 nasopharyngeal cancer patients was 99.26%, and the maximum deviation of intra-fractional radiotherapy was below 0.5%. Conclusions: The function of dose reconstruction and independent calculation of the Mobius system yeilds the same accuracy with the treatment planning system, which can quickly perform three-dimensional independent dose verification in the clinical radiotherapy plan and accelerator log file-based three-dimensional dose verification throughout the treatment, thereby guarantting and providing the safe and reliable technical support for clinical treatment. (authors)