碳离子束FLASH照射实验束流配送方式的研究

Research on the beam delivery method of carbon ion beam FLASH irradiation experiment

目的:改进一套临床碳离子治疗系统的束流配送方式,并测试其性能,以满足使用碳离子束进行FLASH细胞及动物实验的条件。方法:使用碳离子治疗系统的垂直束,通过缩短同步加速器束流引出时间提高流强的方法,来获取超高剂量率。将高流强的束流在深度方向采用脊形过滤器展宽,横向使用点扫描技术扩展,可形成细胞学实验和动物实验所需的射野。测量射野平坦度、半影、吸收剂量、平均剂量率等,以验证束流性能是否满足要求。结果:深度方向展宽的Bragg峰和设计一致,横向剂量曲线测量得到的射野平坦度和半影等参数满足实验要求。扩展后在20 mm×20 mm×10 mm的靶体积内,射野吸收剂量达到8 Gy,射野平均剂量率>60 Gy/s,最大可以达到100 Gy/s;30 mm×30 mm×10 mm靶体积内,射野吸收剂量为4 Gy,部分能量的射野平均剂量率>40 Gy/s,实验中可选择剂量率适合的能量进行照射。结论:经过对束流配送方法的改进,已经能够在同步加速器上实现碳离子FLASH细胞学实验的条件,通过对加速器的改进实现加速粒子数倍增后,剂量率和剂量都可以达到目前文献报道的FLASH动物实验条件。

Objective To perform FLASH irradiation experiments on cells and animals with carbon ion beams by updating the beam conditions and testing the performance of a clinical carbon ion therapy system.Methods By using the vertical beam of the carbon ion therapy system and shortening the synchrotron beam extraction time to increase the current intensity,ultra-high dose rate beam could be achieved.Spreading the high current beam in the depth direction using a ridge filter and expanding it horizontally using point scanning technology could form the required field for cellular and animal experiments.The field flatness,penumbra,absorbed dose,average dose rate and other parameters were measured to verify whether the beam performance met the requirements.Results The spread-out Bragg peak in the depth direction was consistent with the design,and the parameters such as field flatness and penumbra obtained by the measured lateral dose curve met the experimental requirements.After expansion,within a target volume of 20 mm×20 mm×10 mm,the absorbed dose in the field reaches 8 Gy,with the equivalent field dose rate of over 60 Gy/s and the maximum could reach 100 Gy/s.Within a target volume of 30 mm×30 mm×10 mm,the absorbed dose in the field is 4 Gy,and the equivalent filed dose rate of some energy in the field is greater than 40 Gy/s.In the experiment,the energy with a suitable dose rate can be selected for irradiation.Conclusion After beam optimization,the carbon ion FLASH irradiation conditions for cytology and animal experiments can be realized on synchrotrons,and the beam performance parameters can meet the experimental requirements.