Effects of different parameter settings on Gamma passing rate in EPID-based IMRT verification for cervical cancer(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2021年第8期
- Page:
- 935-939
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Effects of different parameter settings on Gamma passing rate in EPID-based IMRT verification for cervical cancer
- Author(s):
- ZHENG Xuliang; XING Xiaofen; CUI Tong; ZHANG Jun; PENG Jinxin
- Department of Radiation Oncology, Shanxi Provincial Cancer Hospital, Taiyuan 030013, China
- Keywords:
- Keywords: cervical cancer electronic portal imaging device Gamma passing rate
- PACS:
- R815.6
- DOI:
- DOI:10.3969/j.issn.1005-202X.2021.08.003
- Abstract:
- Abstract: Objective To verify the Gamma passing rates of radiotherapy plans in 80 patients with cervical cancer after operation using Varian electronic portal imaging device (EPID) for analyzing differences in Gamma passing rates between two accelerators and different gantry angles, and to discuss the effects of 3 different parameter settings on the Gamma passing rate, thereby providing a practical theoretical basis for plan verification. Methods Seven-field treatment plan was developed for each patient, and the corresponding verification plan was created. Plans were verified at two accelerators of the same type (Varian Unique 1, 2), and verification images were also obtained. Portal Dosimetry (PD) was used to obtain the Gamma passing rates under different parameter settings (standard dose difference and distance to agreement), and then the obtained Gamma passing rates were statistically analyzed. Results Parameter settings included PD_Global/PD_Local 1%/1 mm, 2%/2 mm, 3%/3 mm, with a dose threshold of 10%. (1) When the parameter was set as PD_Global（2%/2 mm, 1%/1 mm), the Gamma passing rate of Gan=0° was the highest and the Gamma passing rates of Gan=104°, 256° were lower than others (P<0. 05). The Gamma passing rate of Gan=0° was the lowest when adopting PD_Local (3%/3 mm, 2%/2 mm, 1%/1 mm) (P<0.05). (2) When the parameter was set as PD_Global 1%/1 mm and PD_Local 1%/1 mm, the Gamma passing rate of Unique-2 was higher than that of Unique-1 (P<0.05). Conclusion Strict parameter setting can reflects the effect of gantry angle, accelerator performance on Gamma passing rate. Relevant analytical conditions should be added for different tumor sites. In order to improve radiotherapy accuracy, physicists need to increase the detection frequency of the equipment parameters such as imaging devices, gantry angular displacement, multileaf collimator positioning accuracy, and stricter parameters and limits of Gamma passing rate should be established through the accumulation of large amounts of data and combination with clinical information.
Last Update: 2021-07-30