Effects of carbon fiber couch of TrueBeam accelerator in flattening filter-free and flattening filter modes on radiotherapy dose(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2019年第8期
- Page:
- 867-871
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Effects of carbon fiber couch of TrueBeam accelerator in flattening filter-free and flattening filter modes on radiotherapy dose
- Author(s):
- SHI Yinghua; GE Chao; WANG Libo; XIA Wenming; CHEN Kunzhi; YANG Xu; DONG Lihua; WANG Huidong; GAO Yan
- Department of Radiotherapy, the First Bethune Hospital of Jilin University, Changchun 130021, China
- Keywords:
- ; Keywords: carbon fiber couch; flattening filter mode; flattening filter-free mode; penetration factor; surface dose
- PACS:
- R815.6；R312
- DOI:
- DOI:10.3969/j.issn.1005-202X.2019.08.001
- Abstract:
- Abstract: Objective To evaluate the dosimetric effects of carbon fiber couch of Varian TrueBeam accelerator in flattening filter-free (FFF) and flattening filter (FF) modes on the central and surface doses of a phantom. Methods The solid water phantom of 30 cm×30 cm×20 cm was placed on 3 parts (thin, medium and thick) of treatment couch, and the center of the phantom was set at the isocenter of gantry. The isocenter dose was measured with German IBA FC65-G ionization chamber. In this study, 6/10 MV photon beam with FF/FFF models, a standard field of 10 cm×10 cm and isocentric irradiation were adopted. Taking the measured dose with beam incidence angle which was changed in every 10° gantry angles between 0° and 80° as reference, the penetration factor was obtained by calculating the ratio between the dose in the range of 100°-180° and the corresponding reference dose. EBT3 Gafchromic film was placed at the surface and bottom of the phantom, with a corresponding gantry angle of 0° and 180°. Finally, the corresponding percent depth doses were analyzed. Results The penetration factor were 0.956 6-1.0000, 0.955 4-1.000 0 and 0.954 8-1.000 0 at the thin, medium and thick parts of treatment couch. The penetration factor was minimal at 6 MV-FFF 120° for thin and thick parts of treatment couch, and at 6 MV-FFF 130° for the thick part of treatment couch. Compared with 0° irradiation, 180° irradiation with 6 MV-FFF, 6 MV, 10 MV-FFF and 10 MV X rays increased the surface doses from 30.6%, 24.1%, 18.3% and 14.1% to 95.4%, 93.0%, 83.0% and 79.6%, respectively. Conclusion The use of carbon fiber couch not only reduces tumor dose, but also increases surface dose. Moreover, the dosimetric effect of FFF modes is significantly larger than FF mode. The application of virtual carbon fiber couch in treatment planning system can reduce the dosimetric effects caused by treatment couch.
Last Update: 2019-08-26