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目的 对单个等中心上下半野照射鼻咽癌颈部剂量分布特征进行研究。方法 在加速器上用 6MVX射线分别按常规技术和单个等中心上下半野技术方法对剂量体模进行模拟照射 ,用热释光和胶片剂量仪测出面颈野和颈锁野衔接层面相关剂量及剂量重叠情况。对用 2种照射技术治疗的 2组患者定时拍摄验证片比较摆位重复性。结果 热释光测量结果显示单中心技术在照射野衔接层面平均剂量 (1.0 1Gy)接近剂量DT1Gy,而常规分野技术在照射野衔接层面平均剂量 (1.0 9～ 1.13Gy)有 10 %左右的超出 ,胶片显示单中心技术照射在颈部的等剂量分布较均匀合理 ,无明显高剂量区出现。验证片证实单中心技术的照射野重叠 (1mm)和摆位偏移 (0 .5mm)很小 ,分别优于常规分野技术 (6～ 14mm和 3mm)。结论 单中心上下半野照射技术在照射野衔接处可以得到比较准确和均匀的剂量分布 ,减少了摆位误差并有较好的摆位重复性 ,是一种值得推广的照射技术。
Objective To study the neck dose distribution of nasopharyngeal carcinoma in upper and lower half of a single isocenter. Methods The dose phantom was irradiated by 6MV X-ray with 6MV X-ray respectively according to the conventional technique and the single center-half technique. The dose and dose of surface-neck and neck-lock junction were measured by thermoluminescence and film dosimeter Overlap The two groups of patients treated with two irradiation techniques time-lapse verification tablets compared positioning repeatability. Results The results of thermoluminescence showed that the average dose (1.01Gy) approached the dose of DT1Gy in the single-center technique at the convergence level of irradiation field, while the conventional technique exceeded the average dose (1.09-1.13Gy) in the irradiation field by about 10% Film shows that the single-center technique irradiation in the neck of the equal dose distribution is more uniform and reasonable, no obvious high-dose area. The verification chip confirmed that the overlap of the irradiation field (1mm) and the setup offset (0.5mm) of the single-center technique are very small, which are superior to the conventional separation techniques (6-14mm and 3mm respectively). Conclusions Single center irradiation technique can obtain a more accurate and uniform dose distribution at the irradiation field convergence point, reduce the setup error and have better positioning repeatability, which is a kind of irradiation technique worthy of promotion.