This study aimed to evaluate dosimetrically the feasibility of saving both the lens and the ciliary body in the treatment of a choroidal melanoma by using spatially fractionated proton minibeams. A multi-slit brass collimator was designed by using Monte Carlo simulation data and was fabricated with a 0.4-mm beam opening and a 1.1-mm center-to-center distance. A phantom was also fabricated for proton beam dosimetry, involving five polymethylmethacrylate (PMMA) plates of 2 mm and 8 mm thicknesses, respectively. The peak-to-valley dose ratio (PVDR) of the proton minibeams was used to validate the feasibility of lens and ciliary body sparing. The typical single-scattered proton beam for treating a patient with a choroidal melanoma was delivered to Gafchromic EBT3 films in the phantom after having passed through the multi-slit: the energy of proton beam was 60 MeV, and its depth dose profile was a full spread-out Bragg peak (SOBP). The average dose at mid-depth of the SOBP was approximately 3 CGE with ±3% of ripple. Dosimetric evaluation showed the PVDR depended on the air gap strongly. It varied from 3.4 to 1.1 in the air gap range from 2 mm to 62 mm. The PVDR values at PMMA depths of 2, 12, 22, and 32 mm were 2.0, 1.5, 1.1, and 1.06, respectively. This result shows that a spatially fractionated proton beam might save the lens and ciliary body seated at a shallow depth in the eye ball when a choroidal melanoma is treated using proton minibeam radiotherapy.

中文翻译：

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质子微束放射治疗脉络膜黑色素瘤的初步剂量学研究

本研究旨在通过使用空间分离质子微束在治疗脉络膜黑色素瘤中对保存晶状体和睫状体的可行性进行剂量学评估。使用蒙特卡罗模拟数据设计了多缝黄铜准直器，其光束开口为 0.4 毫米，中心距为 1.1 毫米。还为质子束剂量测定制作了一个体模，分别涉及五个厚度为 2 毫米和 8 毫米的聚甲基丙烯酸甲酯 (PMMA) 板。质子微束的峰谷剂量比 (PVDR) 用于验证晶状体和睫状体保留的可行性。用于治疗脉络膜黑色素瘤患者的典型单散射质子束在通过多缝后被传送到体模中的 Gafchromic EBT3 膜：质子束的能量为 60 MeV，其深度剂量分布为完全展开的布拉格峰 (SOBP)。SOBP 中间深度的平均剂量约为 3 CGE，波动为 ±3%。剂量学评估表明 PVDR 强烈依赖于气隙。它在 2 毫米到 62 毫米的气隙范围内从 3.4 到 1.1 不等。PMMA 深度为 2、12、22 和 32 mm 时的 PVDR 值分别为 2.0、1.5、1.1 和 1.06。该结果表明，当使用质子微束放射治疗脉络膜黑色素瘤时，空间分割质子束可能会挽救位于眼球较浅深度的晶状体和睫状体。剂量学评估表明 PVDR 强烈依赖于气隙。它在 2 毫米到 62 毫米的气隙范围内从 3.4 到 1.1 不等。PMMA 深度为 2、12、22 和 32 mm 时的 PVDR 值分别为 2.0、1.5、1.1 和 1.06。该结果表明，当使用质子微束放射治疗脉络膜黑色素瘤时，空间分割质子束可能会挽救位于眼球较浅深度的晶状体和睫状体。剂量学评估表明 PVDR 强烈依赖于气隙。它在 2 毫米到 62 毫米的气隙范围内从 3.4 到 1.1 不等。PMMA 深度为 2、12、22 和 32 mm 时的 PVDR 值分别为 2.0、1.5、1.1 和 1.06。该结果表明，当使用质子微束放射治疗脉络膜黑色素瘤时，空间分割质子束可能会挽救位于眼球较浅深度的晶状体和睫状体。