(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To analyze the patient-specific dosimetric verification results of 50 stereotactic body radiotherapy (SBRT) plans and to investigate the sensitivity of the result to three factors: interpolation of measurement data, size of dose calculation grid and assessment threshold.
Methods: The dosimetric verification results of SBRT plans for 50 patients from February 2012 to November 2018 were retrospectively analyzed. The linear interpolation (1 mm) and non-interpolation (7.62 mm) were selected for measured data interpolation. Dose calculation grid size of 1.0 mm, 2.5 mm and 4.0 mm was selected, respectively. The threshold of dose assessment was selected as 10%, 20% and 30%, respectively. Three criteria of γ analysis were selected: 2%/2 mm, 3%/2 mm and 3%/3 mm.
Results: To evaluate the effects of interpolation on γ passing rate, linear interpolation and non-interpolation were selected for the measured data. With different criteria (2%/2 mm, 3%/2 mm and 3%/3 mm), the average γ passing rate was 86.30% ± 7.30% and 93.67% ± 5.54%, 94.09% ± 4.37% and 97.73% ± 3.87%, 97.69% ±2.16% and 99.06% ± 1.70%, respectively. For the effects of dose calculation grid size, γ passing rate changes were separately evaluated. Compared with dose calculation grid size of 1 mm, the average γ passing rate of 2.5 mm and 4.0 mm with different criteria decreased by 3.79%, 1.92%, 0.80%and 6.51%, 5.97%, 3.50%, respectively. Significant decreasing was observed (P <0.005). For the effects of dose assessment threshold, the average γ passing rate 20% and 30% with different criteria was compared with that the threshold 10%. Significant decreasing of 2.40%, 0.96%, 0.57% and 3.98%, 1.74% 0.91%was found, respectively (P <0.005).
Conclusion: Interpolation, dose calculation grid size and dose assessment threshold all have an prominent impact on the dose verification results, and need to be considered during dosimetric verification of stereotactic radiotherapy.
Keywords
Stereotactic Radiosurgery, Data Interpolation, Treatment Verification
Taxonomy
TH- Radiation dose measurement devices: Multi-dimensional diode/chamber arrays
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