鼻咽癌锥形束CT引导方案与摆位误差的相关性

Correlation between cone beam computed tomography-guided scheme and setup errors in nasopharyngeal carcinoma

目的探讨鼻咽癌放疗过程中锥形束CT（CBCT）引导方案摆位误差变化规律。方法选择2014年11月至2015年8月在广东省梅州市人民医院行根治性放疗的87例鼻咽癌患者，所有患者放疗期间采用Elekta Synergy S型直线加速器配备的千伏级CBCT行10次治疗前扫描，分析左右（X）方向、头脚（Y）方向、垂直（Z）方向上的摆位误差变化规律。结果随着CBCT扫描次数的增加，鼻咽癌患者X方向、Y方向10次摆位误差均值组间比较，差异均无统计学意义（均P〉0.05）。Z方向前6次摆位误差均值组间比较，差异均无统计学意义（均P〉0.05），但从第7次开始，Z方向的系统误差呈增大趋势，第7、8、9、10次的系统误差依次为0.140、0.292、0.461、0.640 mm，且前7次摆位系统误差组间均值比较，差异有统计学意义（H=15.232，P=0.019），前8、9、10次摆位系统误差均值组间比较，差异亦有统计学意义（均P〈0.05）。结论非连续的CBCT可以降低系统误差和随机误差，根据摆位误差变化规律选择合理的使用频率是鼻咽癌较理想的CBCT引导方案。

ObjectiveTo study the more safe and accurate guidance scheme of cone beam computed tomography （CBCT） in nasopharyngeal carcinoma.MethodsCBCT was regularly performed on 87 patients with nasopharyngeal carcinoma in Meizhou People＇s Hospital from November 2014 to August 2015. For each patient, 10 times CBCT scans were obtained pre-treatment. All the setup errors were obtained and analysed on the orientation X （left and right）, Y （head and foot） and Z （vertical） axis.ResultsWith the increase of the number of CBCT scans, there was no statistically significant difference among the mean setup errors of the 10 times scans in X （left and right） and Y （head and foot） directions （all P 〉 0.05）. And there was no statistically significant difference among the mean setup errors of 6 times scans in Z （vertical） direction, but from the beginning of the 7th, the systematic error in Z direction was increasing, the system error of the 7th, 8th, 9th, 10th time was 0.140, 0.292, 0.461, and 0.640 mm. Moreover, the difference of the mean systematic errors among the first 7 times was statistically significant （H = 15.232, P = 0.019）, and the differences of the mean systematic errors among the first 8, 9 and 10 times were statistically significant （all P 〈 0.05）.ConclusionsNon-consecutive scans of CBCT could reduce the systematic and random errors. The appropriate frequency of application of CBCT based on the change law of setup errors is an ideal CBCT guidance scheme for nasopharyngeal carcinoma.