ABSTRACT
Objective:To compare the effects of parameters, such as planning target volume (PTV), calculation grid size, and dose threshold, on the dosimetric verification result of three dosimetric verification systems ArcCHECK, SRS MapCHECK, and 3DMap for stereotactic body radiation therapy (SBRT).Methods:Based on the dosimetric verification result of the SBRT plans of 50 patients, this study compared the effects of PTV (<25 cm 3 and ≥25 cm 3), calculation grid size (1.0, 1.5, and 2.0 mm), and dose threshold (5%, 10%, and 15%) on the γ passing rates of the three dosimetric verification systems at five criteria, i. e., 3 mm/3%, 3 mm/2%, 3 mm/1%, 2 mm/3%, and 2 mm/2%. Results:The changes in PTV affected 3DMap more significantly. With an increase in PTV, the γ passing rates of 3DMap at the criteria of 3 mm/3%, 3 mm/2%, 2 mm/3%, and 2 mm/2% increased by 2.2%, 2.2%, 4.4%, and 4.7% ( t=-2.76, -2.17, -4.72, -3.86, P<0.05), respectively. The increase in the calculation grid from 1.0 mm to 1.5 mm had greater effect on MapCHECK, with the γ passing rates at the criteria of 3 mm/3%, 3 mm/2%, 3 mm/1%, 2 mm/3% and 2 mm/2% decreased by 0.7%, 1.1%, 1.7%, 0.9%, 1.5% ( t=-6.15, -6.23, -5.98, -5.11, -8.34, P<0.05), respectively. The increases in the calculation grid from 1.0 mm to 2.0 mm had greater impact on ArcCHECK, with the γ passing rates at the criteria of 3 mm/3%, 3 mm/2%, 3 mm/1%, 2 mm/3%, 2 mm/2% decreased by 1.0%, 1.7%, 2.4%, 1.7%, 2.7% ( t=-4.75, -7.3, -8.63, -7.11, -8.26, P<0.05), respectively. The increase in the dose threshold from 5% to 10% had greater impact on ArcCHECK, with the γ passing rates at the criteria of 3 mm/3%, 3 mm/2%, 2 mm/3% and 2 mm/2% decreased by 1.1%, 1.4%, 2.5%, and 3.0% ( t=5.20, 5.68, 8.17, 9.99, P<0.05), respectively. Moreover, the increase in the dose threshold from 5% to 15% had more impact on 3DMap, with the γ passing rates at the criteria of 3 mm/3%, 3 mm/2%, 2 mm/3%, and 2 mm/2% decreased by 1.6%, 1.7%, 2.8%, and 3.2% ( t=3.25, 2.98, 4.40, 4.21, P<0.05), respectively. Conclusions:Target volume, calculation grid, and dose threshold are influencing factors in the dosimetric verification of three dosimetric verification systems for SBRT. Therefore, the effects of these parameters should be considered for different verification systems in clinical applications.
ABSTRACT
Objective@#To analyze the patient-specific dosimetric verification result of stereotactic body radiotherapy (SBRT) plans, and to investigate the sensitivity of the result to three factors: interpolation of measured data, size of dose calculation grid and assessment threshold.@*Methods@#The dosimetric verification results of SBRT plans of 50 patients were retrospectively analyzed to evaluate the impact of the following factors. The linear interpolation (1.00 mm) and non-interpolation (7.62 mm) were applied to measured data respectively. Three dose calculation grid sizes of Eclipse planning system, i. e., 1.0 mm, 2.5 mm and 4.0 mm were compared 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@#Under criteria of 2%/2 mm, 3%/2 mm and 3%/3 mm, the average γ passing rates were (86.3±7.3)% and (93.7±5.6)%, (94.1±4.4)% and(97.7±3.9)%, (97.7 ±2.2)% and (99.1±1.7)%, respectively, with and without linear interpolation. Relative to the 1.0 mm reference grid, the grids of 2.5 mm and 4.0 mm significantly decreased γ passing rates by 3.8%, 1.9%, 0.8% (t=8.41, 9.06, 5.30, P<0.05) and by 6.5%, 6.0%, 3.5% (t=-13.76, -13.15, -9.80, P<0.05) under criteria of 2%/2 mm, 3%/2 mm and 3%/3 mm, respectively. Relative to the 10% reference threshold, the shresholds of 20% and 30% significantly decreased γ passing rates by 2.4%, 1.0%, 0.6%(t=-8.60, -5.86, -4.68, P<0.05) and by 4.0%, 1.7%, 0.9% (t=-9.45, -6.66, -5.06, P<0.05) under criteria of 2%/2 mm, 3%/2 mm and 3%/3 mm, respectively.@*Conclusions@#Interpolation, dose calculation grid size and dose assessment threshold are influential factors of dose verification result, and need to be considered during dosimetric verification of stereotactic radiotherapy patients.
ABSTRACT
Objective To analyze the patient-specific dosimetric verification result of stereotactic body radiotherapy ( SBRT ) plans, and to investigate the sensitivity of the result to three factors:interpolation of measured data, size of dose calculation grid and assessment threshold. Methods The dosimetric verification results of SBRT plans of 50 patients were retrospectively analyzed to evaluate the impact of the following factors. The linear interpolation ( 1. 00 mm) and non-interpolation ( 7. 62 mm) were applied to measured data respectively. Three dose calculation grid sizes of Eclipse planning system, i.e., 1. 0 mm, 2. 5 mm and 4. 0 mm were compared 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 Under criteria of 2％/2 mm, 3％/2 mm and 3％/3 mm, the average γ passing rates were (86. 3±7. 3)％ and (93. 7±5. 6)％, (94. 1±4. 4)％ and(97. 7±3. 9)％, (97. 7 ±2. 2)％ and (99. 1±1. 7)％, respectively, with and without linear interpolation. Relative to the 1. 0 mm reference grid, the grids of 2. 5 mm and 4. 0 mm significantly decreased γ passing rates by 3. 8％, 1. 9％, 0. 8％ ( t=8. 41, 9. 06, 5. 30, P<0. 05) and by 6. 5％, 6. 0％, 3. 5％ ( t=-13. 76, -13. 15, -9. 80, P<0. 05) under criteria of 2％/2 mm, 3％/2 mm and 3％/3 mm, respectively. Relative to the 10％ reference threshold, the shresholds of 20％ and 30％ significantly decreasedγpassing rates by 2. 4％, 1. 0％, 0. 6％(t=-8. 60, -5. 86, -4. 68, P<0. 05) and by 4. 0％, 1. 7％, 0. 9％ (t=-9. 45, -6. 66, -5. 06, P<0. 05) under criteria of 2％/2 mm, 3％/2 mm and 3％/3 mm, respectively. Conclusions Interpolation, dose calculation grid size and dose assessment threshold are influential factors of dose verification result, and need to be considered during dosimetric verification of stereotactic radiotherapy patients.
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In this study, we evaluated the effect of grid size on dose calculation accuracy using 2 head & neck and 2 prostate IMRT cases and based on this study's findings, we also evaluated the efficiency of a 2D diode array detector for IMRT quality assurance. Dose distributions of four IMRT plan data were calculated at four calculation grid sizes (1.25, 2.5, 5, and 10 mm) and the calculated dose distributions were compared with measured dose distributions using 2D diode array detector. Although there was no obvious difference in pass rate of gamma analysis with 3 mm/3% acceptance criteria for the others except 10 mm grid size, we found that the pass rates of 2.5, 5 and 10 mm grid size were decreased 5%, 20% and 31.53% respectively according to the application of the fine acceptance criteria, 3 mm/3%, 2 mm/2% and 1 mm/1%. The calculation time were about 11.5 min, 4.77 min, 2.95 min, and 11.5 min at 1.25, 2.5, 5, and 10 mm, respectively and as the grid size increased to double, the calculation time decreased about one-half. The grid size effect was observed more clearly in the high gradient area than the low gradient area. In conclusion, 2.5 mm grid size is considered acceptable for most IMRT plans but at least in the high gradient area, 1.25 mm grid size is required to accurately predict the dose distribution. These results are exactly same as the precious studies' results and theory. So we confirmed that 2D array diode detector was suitable for the IMRT QA.