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在基于被动式束流配送系统的分层适形重离子治疗当中,需要利用微型脊形过滤器(mini ridge filter,mini-RF)将单能重离子束Bragg峰展宽为峰区近似高斯分布的微小展宽峰(mini spread-out Bragg peak,mini-SOBP),从而达到减少照射分层数及照射时间的目的。采用较宽的mini-SOBP可以有效减少照射分层数,但会增大展宽Bragg峰(SOBP)远端剂量跌落距离,增加对靶区后方正常组织或危及器官的辐照剂量。这一问题可以通过双mini-SOBP的组合照射方法来解决。使用2种mini-RF对单能重离子束Bragg峰略微展宽得到2种半高宽(FWHM)且剂量分布近似高斯分布的mini-SOBP,通过基于放射生物学模型的剂量优化,证实了在SOBP平顶区按生物有效剂量均匀和物理吸收剂量均匀的展宽情况下,双mini-SOBP组合照射方法均可以在减少照射分层数的同时较大幅度地减小SOBP远端剂量跌落距离。
In layered conformal-based heavy ion therapy based on passive beam delivery systems, the Bragg peak of a single energy heavy ion beam needs to be broadened to a small Gaussian distribution with a peak area using a mini ridge filter (mini-RF) Mini spread-out Bragg peak (mini-SOBP), so as to reduce the number of irradiation layers and the irradiation time. The use of a wider mini-SOBP can effectively reduce the number of irradiation layers but increase the dose fall distance at the far end of the extended Bragg peak (SOBP) and increase the irradiation dose to the normal tissue or organ at the rear of the target. This problem can be solved by a combination of dual mini-SOBP irradiation method. The mini-SOBP with two FWHMs and an approximate Gaussian distribution of the dose distribution was slightly broadened using two mini-RFs for the single-energy heavy ion beam Bragg peak. The dose optimization based on the radiobiological model demonstrated that in the SOBP In the flat-top area, the double mini-SOBP combination irradiation method can significantly reduce the far-end dose fall distance of SOBP while reducing the number of irradiation stratification according to uniform uniform effective dose and physically absorbed dose.