Impact of dose calculation algorithm on magnetic resonance imaging-only radiotherapy for prostate and glioma

Synthetic computed tomography (sCT) enables magnetic resonance imaging (MRI)-only radiotherapy by providing electron density information for dose calculation. While sCT-based planning has been proven sufficiently accurate for convolution-based dose calculation algorithms, linear Boltzmann transport equation (LBTE)-based approaches exhibit higher sensitivity to tissue heterogeneities. This study evaluated the accuracy of both dose calculation algorithm types for MRI-only in prostate and glioma radiotherapy.

Clinical treatment plans for thirty-nine prostate cancer patients and seventeen glioma patients were recalculated on atlas- and deep learning (DL)-based sCTs and conventional CT using convolution- and LBTE-based algorithms. Target dose metrics were analyzed as relative differences, while organs of interest (OOI) dose criteria were evaluated as absolute differences between sCT- and CT-based calculations. Statistical significance was assessed using paired t-tests (α = 0.05).

For target volumes, statistically significant differences between sCT- and CT-based calculations were observed for both dose calculation algorithms (p < 0.001). In prostate patients, mean differences in target dose metrics were ≤ 1.4% for the LBTE-based algorithm and ≤ 0.5% for the convolution-based algorithm. Slightly smaller dose differences were observed for glioma patients, ≤ 0.8% and ≤ 0.5%, respectively. OOI dose differences were small (≤ 0.6%). The LBTE-based algorithm consistently yielded the largest dose differences between CT and sCT.

Although the LBTE-based approach demonstrated higher sensitivity to sCT-related CT number discrepancies than the convolution-based dose calculation algorithm, the resulting dose differences remained within clinically acceptable limits, supporting the robustness of MRI-only radiotherapy for both atlas- and DL-based sCTs.