分化型甲状腺癌患者口服^(131)I后体内活度变化及剂量水平

Activity variation and dose level in patient's body with differentiated thyroid cancer after ^(131)I therapy

目的研究^(131)I治疗分化型甲状腺癌(DTC)患者体内放射性活度及外部剂量水平的变化规律,分析二者之间的关系,并估算400 MBq患者剂量当量率的修正因子。方法研究对象为43例甲状腺全切术后,首次行^(131)I"清甲"治疗的DTC患者,服药量为1850~3700 MBq,平均服药量(2405±777)MBq。分别于口服^(131)I后2、6、20、22、24、27、30、44、46、48、54、68及72 h,测定患者的体内剩余放射性活度以及患者前部0.3、1及3 m处的剂量当量率。结果患者服^(131)I后的体内剩余放射性活度随时间变化函数为A=A_(0)(1.03316e^(-0.0624t)+0.01717)。可估算出"清甲"治疗的DTC患者有效半减期为12.19 h,体内放射性活度降至400 MBq仅需26.4~38.9 h。患者服用^(131)I后距其0.3、1及3 m的标准化剂量当量率随时间变化函数分别为:Ḣ_(0.3)=127.2207e^(-0.0548t)+3.76571、Ḣ_(1)=30.2258e^(-0.0644t)+0.82467、Ḣ_(3)=4.1619e^(-0.0615t)+0.16797。患者服^(131)I后体内剩余放射性活度与1 m处剂量当量率呈正相关(r=0.982,P<0.05),函数为Ḣ_(1)=0.025A+1.245。DTC患者体内剩余活度分别为1000、700和400 MBq时,距患者1 m处对应的剂量当量率分为26.2、18.7和11.2μSv/h。估算活度为400 MBq的患者0.3、1及3 m处剂量当量率的修正因子分别为0.25、0.49及0.70。结论服用^(131)I活度在3700 MBq以下的DTC患者仅需住院2日便可达到出院标准。当DTC患者体内活度降至400 MBq时,其1 m处的剂量当量率远小于25μSv/h。单纯利用点源公式估算患者周围剂量当量率会造成高估的情况,因此对于公式估算患者周围辐射水平时使用的修正因子还需进一步研究,使模型估算结果更贴合实际情况。

Objective To study the variation in activity in patient's body with differentiated thyroid cancer(DTC)treated with^(131)I and external dose level,analyze the relationship between the both,and estimate the correction factor for the dose equivalent rate for the patients with residual activity of 400 MBq.Methods A total of 43 DTC patients who received^(131)I therapy for the first time after total thyroidectomy were studied.The dose was 1850-3700 MBq and average dose was(2405±777)MBq.The measurements of residual activity in patient's body and of dose equivalent rate at 0.3,1 and 3 m in front of the patients were performed at 2,6,20,22,24,27,30,44,46,48,54,68 and 72 h after administration of^(131)I.Results The residual activity in patient's body after^(131)I therapy varied with time as a function of A=A_(0)(1.03316e^(-0.0624t)+0.01717).It can be estimated that the effective half-life of DTC patients treated with thyroid remnant^(131)I ablation therapy is 12.19 h.It needs only 26.4-38.9 h to reduce the internal activity to the 400 MBq.The functions of variation with time of normalized dose equivalent rate at 0.3,1,and 3 m away from patients were:Ḣ_(0.3)=127.2207e^(-0.0548t)+3.76571;Ḣ_(1)=30.2258e^(-0.0644t)+0.82467;and Ḣ_(3)=4.1619e^(-0.0615t)+0.16797,respectively.There was a positive correlation between residual activity and dose equivalent rate at 1 m(r=0.982,P<0.05),and the function is Ḣ_(1)=0.025A+1.245.When residual activities in DTC patient's body were 1000,700 and 400 MBq,the corresponding dose equivalent rates at 1 m from patients were 26.2,18.7 and 11.2μSv/h,respectively.The correction factors for dose equivalent rate at 0.3,1 and 3 m from patients with 400 MBq were 0.25,0.49 and 0.70,respectively.Conclusions DTC patients with administration of^(131)I activity below 3700 MBq need only to be hospitalized for two days to reach the discharge standards.When the residual activity in DTC patient's body drops to 400 MBq,the dose equivalent rate at 1 m is far less than 25μSv/h.Simply using the point source formula to estimate the dose equivalent rate around the patient will result in overestimation.Therefore,the correction factor used in the estimation of radiation doses to patients by using the formula needs to be further studied so as to make the model-based estimated result more consistent with the actual situation.