HD-V2胶片在超高剂量率电子线射束剂量测量中适用性的研究

A study on the suitability of HD-V2 film in ultra-high dose-rate electron beam dosimetry

目的评估Gafchromic HD-V2胶片在改造常规直线加速器超高剂量率电子线射束中剂量测量的适用性,及其能量和剂量率响应特性。方法使用HD-V2胶片测定改造常规直线加速器电子线的平均剂量率,测量的结果与改进型Markus平板电离室、丙氨酸剂量计进行比较,并使用HD-V2胶片进行初步物理特性测量。利用直线加速器上不同能量射线(6 MV X线和9、16 MeV电子线),剂量范围10~300 Gy,研究HD-V2胶片的能量响应。同时利用直线加速器剂量率(0.03、0.06、0.1 Gy/s)及改造机超高剂量率(范围100~200 Gy/s)射束,研究HD-V2胶片的剂量率响应。结果使用HD-V2胶片测量改造后电子线在源皮距(SSD)100 cm处平均剂量率约为121 Gy/s,与改进型Markus平板电离室、丙氨酸剂量计测量结果一致。改造后超高剂量率射束百分深度剂量(PDD)曲线参数与常规9 MeV电子线相近,离轴剂量分布总体呈现中心轴最高,随离轴距离增加,剂量逐渐下降的特点。对于不同能量6 MV X线和9、16 MeV电子线,剂量范围20~300 Gy,HD-V2胶片无显示能量响应。在常规剂量率(0.03、0.06、0.1 Gy/s)条件下HD-V2胶片无明显剂量率响应,在超高剂量率范围100~200 Gy/s条件下,改造机出束时间与HD-V2胶片测量的剂量之间呈线性关系,无明显剂量率响应。结论本研究结果表明HD-V2胶片适用于改造常规直线加速器超高剂量率射束的剂量测量,且无明显能量及剂量率响应。

Objective To evaluate the usability of Gafchromic HD-V2 film for dose dosimetry in the ultra-high dose-rate(UD)electron beam from a modified medical linac,and to investigate the response between the energy and dose-rate dependence to the film.Methods The HD-V2 film was utilized to measure the average dose-rate of the UD electron beam.The measured result was compared with those by advanced Markus chamber and alanine pellets.And characteristics of the UD electron beam were also measured by HD-V2 film.Energy dependence of HD-V2 film at three beam energies(6 MV X-ray,9 MeV and 16 MeV electron beam)was investigated by obtaining and comparing the calibration curves based on the clinical linear accelerator in the dose range of 10-300 Gy.The dose-rate dependence of HD-V2 film was also studied by varying the dose rate among 0.03 Gy/s,0.06 Gy/s and 0.1 Gy/s,and range of 100-200 Gy/s.Results The measured average maximum dose-rate of 9 MeV UD electron beam at source skin distance(SSD)100 cm was approximately 121 Gy/s using HD-V2 film,consistent with the results by advanced Markus chamber and alanine pellets.The measured percentage depth dose(PDD)curve parameters of the UD electron beam were similar to the conventional 9 MeV beam.The off-axis dose distribution of the UD electron beam showed the highest central axis,and the dose was gradually decreased with the increase of off-axis distance.The energy dependence of HD-V2 film had no dependency of 6 MV and 9,16 MeV while measuring the dose in the range from 20 to 300 Gy.The HD-V2 film had no significant dose-rate dependency at the dose rate of 0.03 Gy/s,0.06 Gy/s and 0.1 Gy/s for the clinical linear accelerator.Likewise,there was also no dose-rate dependence in the range 100-200 Gy/s in the modified machine.Conclusion HD-V2 film is suitable for measuring ultra-high dose rate electron beam,independent of energy and dose rate.