Independent Three-dimensional Dose Calculation from Log Files for Breast VMAT: A Measurement-free Quality Assurance Approach.

PURPOSE: The purpose of this study was to evaluate and validate a measurement-free patient-specific quality assurance (PSQA) approach for volumetric modulated arc therapy (VMAT) breast cancer treatments based on independent three-dimensional (3D) dose calculation from Digital Imaging and Communications in Medicine (DICOM) plans and linear accelerator log files.

MATERIALS AND

METHODS

Seventy clinical breast VMAT plans (36 left-sided and 34 right-sided) were retrospectively analyzed. Independent 3D dose calculations were performed using RadCalc v7.3 based on the DICOM treatment plan (independent dose calculation [IDC] RTPlan) and on delivery log files acquired during the first treatment fraction (IDC LOGs). Results were compared with portal dosimetry (two-dimensional [2D]) and fluence-based analysis. Gamma passing rates (GPRs) were evaluated using 3%/2 mm and 2%/2 mm criteria under action (90%) and tolerance (95%) limits. Receiver operating characteristic (ROC) analysis was performed to evaluate the discriminatory capability. Sensitivity to delivery errors was investigated by introducing controlled multileaf collimator (MLC) shifts (0.5-2.0 mm) and collimator rotation errors (1°-3°).

RESULTS

All PSQA methods met the TG-218 action limit (GPR ≥ 90%) at 3%/2 mm. Under the stricter 2%/2 mm criterion, statistically significant differences among quality assurance methods were observed (P < 0.001). ROC analysis demonstrated superior discriminatory performance for 3D dose-based methods, with area under the curve values of 0.9 for both IDC RTPlan and IDC LOGs, compared with 0.7 for portal dosimetry and 0.5 for fluence-based analysis. Error sensitivity analysis showed that stringent gamma criteria (1%/2 mm and 1%/1 mm) improved detection of subtle MLC and collimator deviations, with log file-based 3D reconstruction outperforming 2D approaches.

CONCLUSIONS

Independent 3D dose calculation is a reliable PSQA approach for breast VMAT, showing higher sensitivity than conventional 2D methods.