不纯泊松分布法在6 MV X射线局部照射剂量估算中的应用

目的从离体和活体两方面探索不纯泊松分布法估算6MV X射线局部受照射剂量和受照射份额的适用性。方法2、4Gy6MV X射线离体照射健康人外周血，受照射份额为20％、50％和80％模拟局部照射；选择2、3Gy6MV X射线局部放射治疗的肿瘤病人，观察首次放射治疗前、后24h外周血淋巴细胞染色体畸变，采用不纯泊松分布法，估算受照射剂量和份额。结果2Gv离体照射50％、80％份额和4Gy照射20％、50％、80％份额的淋巴细胞双着丝粒 环(dic r)畸变呈过分散分布，受照射剂量和份额估算值与实际值基本吻合。单次2Gy盆腔照射、受照射局部红骨髓比例大于20％或3Gy全颅照射放射治疗病人的外周血淋巴细胞dic r畸变呈过分散分布，估算的受照射份额与受照射局部红骨髓比例相接近，较大剂量3Gy放疗时估算的受照射剂量较为准确。患者局部放射治疗后与放射治疗前离体模拟的实验结果都显示较好的一致性。结论采用不纯泊松分布法可以比较准确的估算离体和活体局部受照射剂量和份额，适用于照射剂量较高和照射份额不是太小的低LET射线，受照射局部红骨髓占全身的比例可大致反映局部照射的份额。

Study on estimating the dose for 6 MV X-ray partial-body irradiation using contaminated Poisson technique

Objective To explored the applicability of estimation of the dose and irradiated fraction using the contaminated Poisson method in partial-body simulated exposures and medical exposures with 6 MV X-rays. Methods Partial-body accidental irradiations were simulated by in vitro irradiation of blood from healthy volunteers. The dicentric plus ring aberrations were analyzed by simulated 20%,50%,80% exposure to 2,4 Gy of 6 MV X-rays. Three cancer patients treated with radiotherapy were included in the study. Blood samples of the patients were obtained 24 h before and after treatment. Lymphocytes were cultured in the usual way and metaphases were scored for dicentric and centric ring aberrations. The dose and fraction of cells irradiated were estimated by the contaminated Poisson method. Results The lymphocytes of 80% exposure to 2 Gy and 20%,50%,80% exposure to 4 Gy showed an overdispersed distribution of dicentrics plus rings,and their estimates of irradiation dose and irradiated fraction fell within 30% of the true values in simulated partial-body irradiation. The 2 Gy radiotherapy in the pelvic region and the fraction of irradiated red bone marrow being larger than 20% or radiotherapy in the skull region involving large dose (3 Gy) of 6 MV X-rays produced an overdispersed distribution of dicentrics plus rings. The estimates of irradiated fraction were consistent with those of the fraction of irradiated red bone marrow of the red marrow of whole body. At the higher dose of radiotherapy (3 Gy),the dose estimate,which was 23% off,was a good accuracy to attain. It is noted that the results in vivo were in good agreement with those of simulated partial-body irradiation from cancer patients. Conclusion Contaminated Poisson method will be feasible in the assessment of dose and fraction in accidents involving larger dose partial-body exposure.