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Clinical Evaluation of Dose Calculation Algorithms in Stereotactic Radiation Therapy for Lung Cancer

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Y Tomiyama

Y Tomiyama*, F Araki, T Ono, K Hioki, Kumamoto University, Kumamoto, Kumamoto

SU-E-T-515 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the dose calculation accuracy of the model-based algorithms and a new grid-based Boltzmann equation solver by comparing with Monte Carlo-based algorithm in stereotactic lung irradiation with photon beams.
Methods:The stereotactic body radiation therapy (SBRT) for 20 clinical lung cancer cases was planned using Eclipse (Varian Medical Systems) treatment planning system (TPS). The prescribed dose at isocenter was 48 Gy with 4 fractions and six non-coplanar fields. First, the dose distributions were calculated with analytical anisotropic algorithm (AAA). Next, pencil beam convolution (PBC) and Acuros XB (AXB) based on a new grid-based Boltzmann equation in Eclipse, and Voxel Monte Carlo algorithm (VMC) in iPlan (BrainLAB) were implemented under identical planning conditions as AAA. The dose distributions and dose volume histograms (DVHs) for SBRT were compared among algorithms. Similarly, the dose indices and monitor unit (MU) for the planning target volume (PTV) were also compared. The grid size for all dose calculations was 2.5x2.5x2.5 mm3.
Results:AAA tended to underestimate the PTV dose compared to VMC. In contrast, PBC overestimated the PTV dose in almost all plans. The discrepancies in the D95 evaluation of AAA and PBC for VMC were up to 4.4% and 16.1%, respectively. AXB tended to slightly overestimate the PTV dose compared to VMC but the discrepancy was within 3% in D95. This discrepancy was attributed to differences in material assignments, material voxelization methods, and an energy cut-off for electron interactions. The differences in MU of AXB, AAA and PBC for VMC were up to 1.7%, 3.5%, and 7.8%, respectively.
Conclusion:The dose distributions in lung regions significantly differ based on the principle of the calculation algorithms. The dose calculation accuracy of AXB is comparable to VMC and is more suitable than AAA.

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