Purpose: For high-dose-rate intracavitary brachytherapy for uterine cervical cancer, all procedures including CT imaging, treatment planning, verification, and irradiation are performed within a few hours. Although verification is important for safe treatment, patient-specific quality assurance by secondary check software or measurement are not common. In this study, we developed a system which automatically check treatment plans.
Methods: Reference treatment plans were generated for all patterns of Tandem & Ovoid applicators constructed in air. A software was developed to compare the clinical plans with the reference plan and automatically check the dwell positions, applicator length and offset, weights of dwell time, applicator geometry, and the coordinates of the reference points (Point A). The total dwell time of the reference plan was corrected for source intensity and prescribed dose to predict the total dwell time of the patient plans. Three-dimensional dose distribution was also calculated using the AAPM Task group 43 update 1 equation, and V100%, D90% of target, and D2cc of critical organs were evaluated. 517 plans of 155 cases were retrospectively analyzed.
Results: Calculation time for each plan was 10.4 ± 3.3 s (range 3.3 - 21.1 s). Differences between the predicted and clinical total dwell time were 3.8% ± 5.4% (range -13.1% - 19.1%) and -0.4% ± 11.7% (range -28.9% - 36.5%) for point A prescription and optimized plans, respectively. The ratio of total dwell time to the predicted value showed quadratic correlation with the ratio of V100 of the patient plans to that of reference plans, with an error of 0.0% ±0.5% (range −1.5% - 3.0%). The software successfully detected errors of the plans with deliberate mistakes.
Conclusion: The software developed in this study enabled quick evaluation of the accuracy and validity of the treatment plans even for the optimized plans.