Dosimetric comparison at different gantry and collimator angles in flattening filter-free or flattening filter mode(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2020年第8期
- Page:
- 958-964
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Dosimetric comparison at different gantry and collimator angles in flattening filter-free or flattening filter mode
- Author(s):
- DENG Ying1; 2; ZHANG Meifang1; 2; SUN Wenzhao1; CHEN Li1; YANG Xin1; HUANG Xiaoyan1
- 1. Sun Yat-sen University Cancer Center/State Key Laboratory of Oncology in South China/Collaborative Innovation Center for Cancer Medicine/Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangzhou 510060, China 2. Xinhua College of Sun Yat-sen University, Guangzhou 510520, China
- Keywords:
- Keywords: flattening?ilter-free isocenter dose treatment couch attenuation factor
- PACS:
- R312；R811.1
- DOI:
- DOI:10.3969/j.issn.1005-202X.2020.08.004
- Abstract:
- Abstract: Objective To investigate the effects of different gantry angles or collimator angles on dose output in flattening filter-free (FFF) or flattening filter (FF) mode. Methods Two kinds of photon beam energies (6 MV and 10 MV) in FFF or FF mode in Versa HD linear accelerator were selected for the experiment. The dose measurements were performed at 9 points in the standard field of 10 cm×10 cm. Firstly, after that Mapcheck2 was fixed at the head of the treatment machine with the assistance of an isocentric fixture tool IMF, Mapcheck2 was used to measure the planar doses output by 4 kinds of photon beams at the same angles of gantry and collimator. Then the central axis doses of 4 kinds of photon beams in two cases (at the same gantry angle and different collimator angles at the same collimator angle and different gantry angles) were measured. Finally, the collimator was fixed at 0° and two sets of gantry were set up to pass through the irradiation field (0° and 180°, 90° and 270°). Mapcheck2 was removed, and then solid water and FC65-G ionization chamber were used to build a measurement phantom for measuring the dose of 4 kinds of photon beams in two groups of isocenter parallel-opposed fields. The data collected in this experiment were compared and analyzed by SPSS statistical software. Results When the angles of gantry and collimator were kept consistent, there were significant differences in the planar doses at 9 points irradiated by 4 kinds of photon beams (P6 MV FF =0.020, P6 MV FFF=0.017, P10 MV FF =0.030, P10 MV FFF=0.016). In the cases of different gantry angles or different collimator angles, there was no statistical difference in the central axis dose of 4 kinds of photon beams. The output doses of the 4 kinds of photon beams were significantly different in the parallel-opposed fields of 0° and 180° (P6 MV FF =0.001, P6 MV FFF=0.002, P10 MV FF =0.003, P10 MV FFF=0.001), but there were no significant difference in the parallel-opposed fields of 90° and 270°. Conclusion Versa HD linear accelerator has excellent mechanical isocentric performances. The rotation of both the gantry and the collimator does not affect the accurate output of the central axis dose of the photon beam in practice. In FF mode, the higher the energy is, the smaller the dose attenuation caused by the treatment couch is. Due to the softness of beams and the higher the energy in FFF modes, the output dose is more easily affected by the attenuation effect of the treatment couch, which should be pay attention to in practice.
Last Update: 2020-08-27