Transform routine medical accelerators to achieve Flash-RT and physical performance measurements
10.3760/cma.j.cn113030-20210830-00325
- VernacularTitle:改造常规医用加速器实现Flash-RT及物理性能测量
- Author:
Leijie MA
1
;
Ronghu MAO
;
Hongchang LEI
;
Hong GE
;
Peng CHEN
;
Han LIU
;
Bing LI
;
Hui LUO
Author Information
1. 郑州大学附属肿瘤医院 河南省肿瘤医院放疗科，郑州 450008
- Keywords:
Ultra high dose rate radiotherapy;
Ultra high dose rate;
Medical accelerator;
Modification of accelerator
- From:
Chinese Journal of Radiation Oncology
2022;31(11):1022-1027
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To investigate the feasibility of transforming conventional medical accelerator to achieve ultra-high dose rate required to achieve Flash radiotherapy (Flash-RT), and to understand the physical properties of the Flash-RT beam.Methods:By transforming the Varian 23CX medical accelerator, the radiation average dose rate at the isocenter was not less than 40 Gy/s. The relevant physical measurement scheme was designed to accurately measure the actual radiation dose rate of different source skin distance (SSD) conditions, the percent depth dose (PDD) curve and the off-axis dose distribution of the beam.Results:The average dose rate of 9 MeV electron beam after the transformation was measured using the HD-V2 type film, the average dose rate of 3 s was 97.9 Gy/s, and the average dose rate of 6 s was 99.27 Gy/s. When the SSD was 100 cm, 80 cm and 60 cm, the average dose rate of 9 MeV electron beam after the transformation was 99.3 Gy/s, 168 Gy/s and 297.5 Gy/s, respectively. After the transformation, the R100 of the 9 MeV beam was 2.2 cm underwater, R50 was 3.87 cm underwater, the electron range Rp was 4.58 cm, and the maximum possible energy Ep,0 on the phantom surface was 9.28 MeV. These parameters were slightly higher than those of the conventional 9 MeV beam, manifested with slight increase in the surface dose and widening high dose flat area. The overall deposit dose distribution exhibited the highest central axis and the increase in dose declines from the axis distance. Under the condition that the field size was 20 cm×20 cm and the SSD was 100 cm, the FWHM of the vertical and horizontal off-axis dose distribution curves were 16.6 cm and 16.4 cm, respectively. Conclusion:By transforming conventional medical accelerator, the average dose rate of the beam at the isocycle meets the requirement of Flash-RT, and the average dose rate under the condition of 60 cm SSD is much higher than the requirement of at least 40 Gy/s for Flash-RT.
