5岁儿童仿真模体千伏锥束CT模拟剂量测量

目的 利用热释光探测器（TLD）在CIRS 5岁仿真儿童模体内测量瓦里安千伏锥束CT（kV-CBCT）标准扫描参数下各重要器官剂量，并以此计算有效剂量。方法 挑选一致性在2%以内的TLD并退火。首先基于相同骨盆扫描模式分别用CT电离室和TLD测量CIRS骨盆仿真模体相同体积内的剂量和读数，二者比值即为TLD转换系数；将夹在组织等效插件中的TLD放入儿童模体器官内预留的插孔，在头部、胸部和骨盆3种标准扫描条件模式下，测量器官剂量，并计算有效剂量。结果 TLD转换系数是3.91 mGy/每读数；在头部、胸部和骨盆3种标准扫描条件下，得出全身有效剂量分别是0.63、6.85和19.3 mSv。结论 用CT电离室刻度过的TLD测量kV-CBCT给儿童仿真模体带来的辐射剂量的方法具有可行性。本研究中骨盆扫描条件的有效剂量高于胸部和头部，即该条件预期产生的辐射危害较大，诱发继发性癌症风险较高。

Simulated measurement of doses from kilovoltage cone beam CT based on a 5 years old pediatric anthropomorphic phantom

Objective To use thermoluminescense dosimeters (TLDs) to evaluate the radiation doses to various critical organs in the computerized imaging reference systems (CIRS) 5 years old pediatric anthropomorphic phantom result ing from Varian kilovoltage cone beam CT (kV-CBCT) system based on the standard scanning protocols. Effective dose were also calculated based on dose measurement. Methods A batch of TLDs with consistency no larger than 2% were selected and annealed. First, the doses in an anthropomorphic pelvic phantom were measured using a CT chamber and TLDs, respectively, based on the standard pelvic protocols. The ratio of the both measurements is the TLD conversion coefficient. Other TLDs from the same batch were placed between two tissue-equivalent inserts and placed into the pre-drilled organ cavities of the pediatric phantom. By using standard protocols, the organs dose were measured, based on which the corresponding effective doses were calculated. Results The TLD conversion coefficient was 3.91 mGy/per reading. By using the standard head, low-dose thorax, pelvis protocol, the whole body effective dose was 0.63, 6.85 and 19.3 mSv, respectively. Conclusions It is feasible for using the CT chamber-calibrated TLDs to measure the radiation doses from kV-CBCT to pediatric anthropomorphic phantom. The effective dose in pelvic protocol was higher than in thorax and head protocol, indicating that the pelvic protocol has a penitential to lead to larger radiation damage and higher risk of secondary cancer.