放射性9C束流不同贯穿深度上的线能谱测量

为阐述放射性⁹C束流应用于治癌的物理基础, 运用一个球形生物组织等效正比计数器测量了⁹C束流不同贯穿深度上的线能谱, 得到了沿束流贯穿深度上的剂量平均线能分布. 将实验测量得到的线能谱转换成为不同传能线密度在吸收剂量中所占份额的分布, 得到了该⁹C束流在不同贯穿深度上的剂量平均传能线密度分布. 将生物组织等效正比计数器测量得到的与先前通过平行板正比计数器测量得到的该⁹C束流的剂量平均传能线密度分布进行比较, 发现: 在束流入射通道上, 两者测量数据符合很好, 而在束流Bragg峰附近⁹C离子的沉积区域, 由组织等效正比计数器测量得到的剂量平均传能线密度值大于由平行板正比计数器测量得到的值.

Measurement of Lineal Energy Spectra at Different Penetration Depths along a Radioactive 9C-Ion Beam

It is expected that a radioactive ~9C-ion beam as a type of double irradiation source can increase the curative effect when applying it to heavy-ion cancer therapy, and it has been proved in our previous radiobiological experiment that the relative biological effectiveness (RBE) at the depths around the Bragg peak of a ~9C beam was greater than that of a therapeutic ~(12)C beam at least by a factor of 2. To characterize the physical basis of a ~9C ion beam applying to radiotherapy, a spherical tissue-equivalent proportional counter (TEPC) was used to measure the lineal energy (y) spectra at different depths along a radioactive ~9C-ion beam in this work. Based on the measured spectra, the distribution of dose-averaged lineal energy in depth was derived. Moreover, the measured lineal energy spectra were converted into the distributions of LET in absorbed dose at the different depths. The distribution of dose-averaged LET in depth, therefore, has been obtained for the ~9C beam. The dose-averaged LETs measured with the TEPC and our preceding parellel-plate proportional counter (PPPC) were compared. It has been found that both the measurements agreed well with each other at the entrance channel of the ~9C beam while the dose-averaged LETs by the TEPC were larger than those by the PPPC around the Bragg peak, i.e. the stopping region of the incident ~9C ions. This coincides with the expectation that all of the delayed alpha particles and protons, which are emitted isotropically during the decays of the ~9C ions, can be included by means of the TEPC measurement. The data sets obtained in this work provide a substantial physical basis for revealing the advantages of ~9C beams in cancer therapy.