Abstract

Purpose

The present study investigated the biological effects of spot scanning and passive scattering proton therapies at the distal end region of the spread-out Bragg peak (SOBP) using single cell and multicell spheroids.

Materials and methods

The Geant4 Monte Carlo simulation was used to calculate linear energy transfer (LET) values in passive scattering and spot scanning beams. The biological doses of the two beam options at various points of the distal end region of SOBP were investigated using EMT6 single cells and 0.6-mm V79 spheroids irradiated with 6 and 15 Gy, respectively, by inserting the fractions surviving these doses onto dose-survival curves and reading the corresponding dose.

Results

LET values in the entrance region of SOBP were similar between the two beam options and increased at the distal end region of SOBP, where the LET value of spot scanning beams was higher than that of passive scattering beams. Increases in biological effects at the distal end region were similarly observed in single cells and spheroids; biological doses at 2–10 mm behind the distal end were 4.5–57% and 5.7–86% higher than physical doses in passive scattering and spot scanning beams, respectively, with the biological doses of spot scanning beams being higher than those of passive scattering beams (p < .05).

Conclusions

In single cells and spheroids, the effects of proton irradiation were stronger than expected from measured physical doses at the distal end of SOBP and were correlated with LET increases.

中文翻译：

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单细胞和多细胞球体中扩散布拉格峰远端的被动散射和点扫描质子束的生物效应

 抽象的

 目的

本研究使用单细胞和多细胞球体研究了点扫描和被动散射质子疗法在扩散布拉格峰（SOBP）远端区域的生物学效应。

 材料和方法

Geant4 蒙特卡罗模拟用于计算被动散射和点扫描光束中的线性能量传递 (LET) 值。使用分别用 6 和 15 Gy 照射的 EMT6 单细胞和 0.6 毫米 V79 球体，通过将这些剂量的存活分数插入到剂量存活中，研究了 SOBP 远端区域不同点的两种光束选项的生物剂量。曲线并读取相应的剂量。

 结果

两种光束选项之间 SOBP 入口区域的 LET 值相似，而 SOBP 远端区域的 LET 值有所增加，其中点扫描光束的 LET 值高于被动散射光束的 LET 值。在单细胞和球体中也类似地观察到远端区域生物效应的增加；远端后2~10 mm处的生物剂量分别比被动散射和点扫描光束的物理剂量高4.5~57%和5.7~86%，其中点扫描光束的生物剂量高于被动散射的生物剂量梁 ( p < .05)。

 结论

在单细胞和球体中，质子照射的效果比在 SOBP 远端测量的物理剂量所预期的要强，并且与 LET 增加相关。