发泡胶在鼻咽癌放疗中对剂量分布的影响

目的：研究在鼻咽癌放射治疗中应用发泡胶进行体位固定对剂量分布的影响。方法：随机选取11例应用头颈肩热塑膜联合发泡胶进行体位固定的鼻咽癌患者，在Pinnacle计划系统中将空白CT值设置到发泡胶的CT值以下，以确保发泡胶的CT值被计算在内，作为第一组计划（Plan_F）。同时，复制第一组计划并在定位图像上勾画出发泡胶，设置发泡胶的CT值为0，在不改变射野分布、权重及计划跳数的情况下重新计算剂量分布，作为第二组计划（Plan_N）。比较两组计划的靶区及周围正常组织的剂量分布。结果：对于靶区（GTVnx、GTVnd、GTVrpn、PGTVnx、CTV1、PTV1、CTV2、PTV2）的最小剂量Dmin，最大剂量Dmax，平均剂量Dmean去除发泡胶之后，所测 255组数据中仅有6组数据出现减小（约占2.4%），Dmin、Dmax和Dmean的变化度（%）（X±SD）依次为0.215±0.969、 0.395±0.623和 0.442±0.178，其中除了GTVrpn的Dmin（P=0.727）和Dmax（P=0.142），PGTVnx的Dmin（P=0.623），CTV1 Dmin（P=0.713），CTV2 Dmax（P=0.066），其他评估指标皆显示发泡胶使用组剂量低于去除发泡胶组（P＜0.05）；而对于周围正常组织（脑干、脊髓、左右晶体、左右视神经和腮腺）的Dmean和Dmax去除发泡胶之后，所测的154组数据中仅有14组数据出现减小（约占9.1%），Dmax和Dmean的变化度（%）（X±SD）依次为0.194±0.192 和0.129±0.128，其中除了左、右晶体的平均剂量Dmean（P值分别为0.123和0.06），其余各项指标同样显示发泡胶使用组剂量低于去除发泡胶组（P＜0.05）。结论：发泡胶的使用降低了实际治疗过程中受照部位的剂量，但发泡胶对剂量变化的影响都在目前临床可接受的范围之内。

Effect of Polyurethane Foam on Dose Distribution in Radiotherapy for Nasopharyngeal Carcinoma

Objective:To study the effect of polyurethane foam on the dose distribution in radiotherapy for nasopharyngeal carcinoma(NPC).Methods:Eleven nasopharyngeal carcinoma patients using head and neck thermoplastic mask combined with polyurethane foam were selected randomly.The blank CT value were set below the polyurethane foam in the Pinnacle planning system to ensure the CT value of polyurethane foam were in the calculation(Plan_F).At the same time,Plan_F were copyed and the polyurethane foam on the CT positioning images were sketched.Set the CT value of the polyurethane foam to 0,and recalculate the dose distribution without changing the beam set,beam weight and MUs(Plan_N).The dose distributions of the target areas and organ at risk(OAR)of the two groups were compared.Results:For the target areas(GTVnx,GTVnd,GTVrpn,PGTVnx,CTV1,PTV1,CTV2,PTV2),only 6 of the 255 data measured in the minimum dose(Dmin),the maximum dose(Dmax),and the average dose(Dmean)appeared to decrease(about 2.4%)after removing the polyurethane foam and the changing degree(%)of Dmin,Dmax,and Dmean(X珔±S)were 0.215±0.969,0.395±0.623,and 0.442±0.178,respectively,among which Dmin(P=0.727)and Dmax(P=0.142)of GTVrpn,Dmin(P=0.623)of PGTVnx,Dmin of CTV1(P=0.713)and Dmax of CTV2(P=0.066),all the other evaluation indicators showed that the dosage of the application group was lower than that of the foam re-moval group(P<0.05).For the OARs(brain stem,spinal cord,crystals,optic nerves and parotid)only 14 of the 154 data measured in the Dmax,andDmean appeared to decrease(about 9.1%)after removing the polyurethane foam and the changing degree(%)of Dmax and Dmean(X珔±S)were 0.194±0.192 and 0.129±0.128 respectively.Except for the mean dose(Dmean)of left and right lens(P=0.123 and 0.06,respectively),all the other indicators also showed that the dosage of the foam group was lower than that of the foam removal group(P<0.05).Conclusion:The polyurethane foam reduces the dose distribution during the radiotherapy actually.However,the dose changes were acceptable in the clinical use currently.