| Liu Hongdong,Ding Shouliang,Yang Lu,Wang Bin,Li Yongbao,Huang Xiaoyan.A preliminary study on the out-of-field in-air electron streaming effect in MRI guided radiotherapy[J].Chinese Journal of Radiological Medicine and Protection,2021,41(9):647-652 |
| A preliminary study on the out-of-field in-air electron streaming effect in MRI guided radiotherapy |
| Received:November 30, 2020 |
| DOI：10.3760/cma.j.issn.0254-5098.2021.09.002 |
| KeyWords:MR-linac MRgRT Electron streaming effect Out-of-field dose |
| FundProject:国家自然科学基金项目（11805292）；广东省自然科学基金项目（2018A0303100020） |
| Author Name | Affiliation | E-mail | | Liu Hongdong | Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou 510060, China | | | Ding Shouliang | Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou 510060, China | | | Yang Lu | Radiotherapy Center, Affiliated Tumor Hospital of Guangzhou Medical University, Guangzhou 510095, China | | | Wang Bin | Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou 510060, China | | | Li Yongbao | Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou 510060, China | | | Huang Xiaoyan | Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou 510060, China | huangxiaoy@sysucc.org.cn |
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| Abstract:: |
| Objective To investigate the impacts of electron streaming effect (ESE) on out-of-field dose distribution in 1.5 T MRI-guided radiotherapy. Methods Firstly, the Monaco v5.40.1 (Elekta AB, Stockholm, Sweden) treatment planning system (TPS) was implemented to investigate the ESE in a square field (5 cm×5 cm) at the entry and exit sides of a special homogeneous water phantom. Afterward, a retrospective investigation was conducted into one laryngeal cancer case and one breast cancer case who had been treated on a conventional linear particle accelerator (linac). Then doses were recalculated in the Monaco system using a Unity machine model. Meanwhile, the out-of-field skin dose enhancement induced by ESE was investigated. Results ESE-induced dose variations were observed at both the entry and exit sides of the phantom surface in the presence of a magnetic field, with the ESE on the exit side notably stronger than that on the entry side. For the laryngeal cancer case, the ESE was not notable and had insignificant impacts on the out-of-field skin dose. In contrast, ESE-induced in-air high-dose region outside the body stretched to the chin area for the breast cancer case. This led to the skin dose escalation of the chin at D1 cm3 454.6 cGy. After the application of 1 cm bolus, the corresponding skin dose of the chin D1 cm3 reduced to as low as 113.6 cGy, which is almost equivalent to that in the absence of a magnetic field (D1 cm3=92.5 cGy). Conclusions The ESE in a magnetic field can alter out-of-field dose and lead to local dose enhancement along the electron path. Although the ESE had insignificant impacts on the out-of-field dose of the laryngeal cancer case, it reached the chin area of the breast cancer case. ESE can be effectively shielded by adding protective bolus. |
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