单中心上下半野照射鼻咽癌颈部剂量分布的研究

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6MV X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要性。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（1．01Gy)接近剂量DT1 Gy，而常规分野技术在照射野衔接层面平均剂量（1．09－1．13Gy)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。

Dosimetry of mono-isocenter irradiation technique in radiotherapy for nasopharyngeal carcinoma

Objective To study the dosimetry of mono isocenter irradiation technique in radiotherapy for nasopharyngeal carcinoma. Methods Conventional and mono isocenter irradiation techniques were used to simulate irradiation of the phantom and nasopharyngeal carcinoma patients with Siemens primus linear accelerator equipped with asymmetric collimators. Dose uniformity?isodose distribution and field overlap were measured at the plane of junction with TLD and film dosimeter on the phantom. The reproducibility of the set up was tested on patients with verification films. Results For an applied dose of 1?Gy, TLD dosimetry showed that the mean dose at the junction of fields were 1.01 ?Gy for the mono isocenter technique as compared to 1.09 1.13?Gy for the conventional technique. An ideal isodose distribution at the junction with mono isocenter technique was found by film dosimetry. The reproducibility of the set up was obviously better for the mono isocenter technique, with less field overlap (1mm) and set up deviation (0.5?mm) than those (6 14?mm and 3?mm) of the conventional technique. Conclusions This investigation of junction dosimetry confirms the potential advantage of the mono isocentric technique. Not only does it lead to superior dosimetry in the plane of junction but also associates with a better reproducibility of the set up.