术中放疗的吸收剂量测算方法的研究

Experimental study of dosimetry for intra-operative radiotherapy

目的 研究和比较水、固体水及有机玻璃 3种模体的术中放疗吸收剂量的测算方法。方法 对于 3种模体 ,使用固定在水模体中的电离室对加速器的电子束术中放疗限光筒进行吸收剂量的测算 ,首先选定参考限光筒对所有能量的电子束在源皮距SSD =10 0cm ,水模内射束中心轴上特定深度 ,通过调整加速器使 1cGy =1MU ,然后使用术中放疗及参考限光筒在相同的辐照条件下进行测量 ,即测量术中放疗限光筒的输出因数。对于水模体 ,计算出各限光筒的吸收剂量cGy对应的加速器输出MU数值。并据此计算出固体水模体和有机玻璃模体的各限光筒吸收剂量cGy对应的加速器输出的MU数值。结果 相对于水模体 ,有机玻璃模体的测量误差为 0 2 7%。固体水为0 45 %。

Objective\ To study and compare the dosimetry for intra operative radiotherapy in three kinds of phantoms;water,solid water and polymethyl ones. Methods\ The absorbed dose from electrons of the accelerator with the applicator for intra operative radiotherapy was measured using an ionization chamber fixed on each phantom.The dose at the specific depth in water on the beam central axis was adjusted to 1 cGy per monitor unit for the reference applicator with SSD at 100 cm for all energy levels of electrons.Then the applicator for intra operative radiotherapy was used with no other change,i.e.the output factor was measurd.The values of MU per cGy absorbed dose for all applictors in water phantom were calculated,and these values were used to calculate the MU value per cGy absorbed dose from the output factors for solid and polymethyl phantoms. Results\ The deviation from water phantom was 0.27% and 0.45% for polymethyl and solid water ones,respectively. Conclusion\ Using a polymethyl phantom to measure the absorbed dose may be a practical method when no special water tank or solid water is available.