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 layer-stacking conformal heavy-ion therapy based on passive beam delivery system, it is neces-sary to minimize the layer numbers and reduce irradiation time for layer-stacking conformal heavy-ion therapy. Gaussian shaped mini spread-out Bragg peaks (mini-SOBP) were generated by mini ridge filters (mini-RF) for monoenergetic heavy ion beams. It is effective to minimize the layer number by using mini-SOBPs with the bigger full width at the half maximum (FWHM), but in this way the distal dose fall-off distance of a spread-out Bragg peak (SOBP) will be enlarged, increasing the radiation damage to normal tissue or organ at risk behind the target volume. This issue could be solved by using mini-SOBPs based combinatorial irradiation method. In this study, Gaussian shaped mini-SOBPs with two different FWHMs were generated by two different mini-RFs for monoenergetic heavy ion beams. Based on radiobiological model calculations and dose optimizations, the mini-SOBPs based combinatorial irradiation method was confirmed to reduce the distal dose fall-off distances of SOBPs while minimizing the layer numbers for layer-stacking conformal heavy-ion therapy.
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