A method of describing the characteristics of flattening filter-free photon beam
10.3760/cma.j.issn.1004-4221.2019.01.011
- VernacularTitle:一种描述无均整器光子束特性的方法
- Author:
Guishan FU
1
;
Qian WANG
;
Jiayun CHEN
;
Ke ZHANG
;
Lingling YAN
;
Jianrong DAI
Author Information
1. 国家癌症中心/中国医学科学院北京协和医学院肿瘤医院放疗科
- Keywords:
Flattening filter free photon beam;
Field size;
Off-axis ratio characteristics
- From:
Chinese Journal of Radiation Oncology
2019;28(1):52-56
- CountryChina
- Language:Chinese
-
Abstract:
Objective To establish a novel method of describing the off-axis ratio (OAR) characteristics of the flattening filter-free (FFF) beam.Methods The OAR curves at a depth of 1.5,5,10 and 20 cm were measured for Varian Edge,Elekta VersaHD and Tomotherapy using the water tank.The second derivatives of the OAR in the positive and negative directions were calculated.The center of the line connecting the maximum and minimum second derivatives was defined as the field edge.The distance between the left and right field edges was defined as the dosimetric field size.The OAR curve within the 80％ of dosimetric field size was fitted using the gaussian function and the fitting parameters were adopted to describe the shape of OAR.Results The calculated field size error was less than 0.11 cm and the central axis position error was less than 0.05 cm.The fitting correlation coefficient was greater than O.998.The fitting maximum error of OAR curve did not significantly alter with the depth,whereas slightly increased over the increased field size.The maximum error for a field size of 10,20,30 and 40 cm was 0.49％,0.67％,1.25％ and 2.52％,respectively.Conclusions A method which can independently and accurately describe the OAR characteristics of FFF photon beam is established for the first time,which can calculate the field size of FFF beam and fit the OAR curve of FFF beam using the gaussian function.
