Discussion on application of mean gamma index to Compass 3D dose verification in target area receiving 50% of prescribed dose
10.3760/cma.j.cn112271-20230110-00008
- VernacularTitle:探讨靶区处方剂量50%生成区域的平均γ值在Compass三维剂量验证中的应用
- Author:
Qianqian ZHENG
1
;
Jing CAO
;
Rongrong QU
;
Wenchao GAO
;
Wenzhang CHEN
Author Information
1. 首都医科大学石景山教学医院北京市石景山医院放疗科，北京 100043
- Keywords:
Compass;
3D dose verification;
Mean GI value;
Reconstructed dose
- From:
Chinese Journal of Radiological Medicine and Protection
2023;43(6):469-474
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To explore the value of using the mean gamma index (GI) in targer area receiving 50% prescribed dose as reference in VMAT planned dose verification through model-based dose calculation and measurement-based dose reconstruction.Methods:Based on Compass dose verificantion system, the VMAT plans for 70 patients were validated using two method. The mean GI and passing rate in target area receiving 50% of prescribed dose area for each validation plan were obtained to evaluate its application value in dose validation. First, plan information obtained by TPS calculation was input into the Compass system for performing independent dose calculation based on the accelerator data model, and obtain a three-dimensional dose based on the independent model calculation. The planned fluence measured for each patient′s treatment plan on the accelerator was reconstructed through the Compass system to obtain a three-dimensional dose based on measurement reconstruction. The three-dimensional dose obtained by the two method were compared with the three-dimensional dose calculated by TPS.Results:Combined with the gamma criteria of 3%/3 mm in the error setting condition of GI analysis, the mean GI in the area receiving 50% of prescribed dose was evaluated. GI≤0.4 was classified as PASS, 0.4 < GI ≤ 0.6 as being clinically acceptable, and GI > 0.6 as FAIL. The VMAT planned dose verification for 70 patients showed that the model-based independent calculation was in a better agreement with the TPS calculation. The GI values were all < 0.6: GI≤0.4 for 67 patients and 0.4 90% for 88 patients and < 90% for other 2, all meeting the requirements of clinical dose verification. The model-based independent dose verification is better than the measurement-based reconstructed dose verificantion, and the difference is statistically significant ( t=15.20, 10.71, P < 0.05). Conclusions:The mean GI in target area receiving 50% of prescribed dose can be used as a reference to judge the operatability of clinical plan in clinical dose verification. The mean GI value, in combination with the comprehensive result of gamma passing rate, is more convincing to evaluate dose verification. A combination of model-based dose verification, despite time-saving and labor-saving, and the measurement-based dose verification could become a reliable dose verification method for clinical application.
