Effects of field edge position in a two-dimensional ion chamber array on Gamma passing rate(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2019年第8期
- Page:
- 898-902
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Effects of field edge position in a two-dimensional ion chamber array on Gamma passing rate
- Author(s):
- BAO Chao’en; LU Junli; ZHAI Fushan; CAO Xiaohui; LIU Bing; YANG Yongfeng; LIU Ming; LI Feng
- Department of Oncology, the Third Hospital of Hebei Medical University, Shijiazhuang 050051, China
- Keywords:
- ; Keywords: radiotherapy; ion chamber array; Gamma passing rate; beam edge
- PACS:
- R318.6；R811.1
- DOI:
- DOI:10.3969/j.issn.1005-202X.2019.08.007
- Abstract:
- Abstract: Objective To discuss the effects of the position of a (10×10) cm2 field edge in ion chamber array on the measurement of field sizes and Gamma passing rates. Methods A two-dimensional ion chamber array detector (MatriXX) was used to measure the radiation dose distributions of a (10×10) cm2 field. The position of the field edge was changed by either moving the collimator in X direction or the treatment couch in Y direction while keeping the field size constant. The length variation of the field edge after each 0.1 cm movement was recorded and analyzed with OmniPro I’mRT(1.7) software. The measured dose distribution and the corresponding radiation dose distribution in the treatment planning system of XiO (4.40) were compared. The Gamma passing rates (3% and 3mm) and the minimum acceptance criterion at 100% Gamma passing rate were recorded. Results The length variations of the field edge in the outer space of ion chamber cavity were less than 0.1 cm, and the minimum length variation of the field edge in the middle of two outer spaces was close to 0.05 cm. However, the length variations were larger than 0.1cm when the field edge was in the ion chamber cavity and the length variation at the center of each ion chamber cavity nearly reached the maximum value of 0.2 cm. The analysis on Gamma passing rates (3% and 3 mm) showed that the number of failure points was related to the position of field edge; and that the highest Gamma passing rates were found when the length variation of field edge was maximum or minimum; and that the range of evaluation criterion at 100% Gamma passing rate was 2%/2 mm-6%/3 mm. Conclusion The deviation in the measurement of field size is minimal when the field edge is in the center of the ion chamber and in the middle of two outer spaces, and the Gamma passing rate is the highest when the field edge is as above. Therefore, the effects of the position of high dose gradient area in the ion chamber array on Gamma passing rates during the dose verification of intensity-modulated radiotherapy should be comprehensively considered. It is possible to increase the effectiveness of Gamma passing rate through adjusting the position of dose distribution in the ion chamber array or selecting the optimal evaluation criterion.
Last Update: 2019-08-26