三种调强放疗技术对鼻咽癌患者下颈部亚临床靶区剂量分布的影响

Dosimetric evaluation of lower-neck subclinical target volume in nasopharyngeal carcinoma for three different intensity modulated radiotherapy techniques

目的比较3种不同调强放疔技术对鼻咽癌患者下颈部和锁骨上区亚临床靶区剂量分布均匀性和正常组织受量。方法3种照射方法分别为颈部切线野技术，机架角度分别为180°、150°、120°、90°、270°、240°、210°的7野调强技术，机架角度分别为180°、150°、120°、90°、0°、270°、240°、210°的8野调强技术。利用剂量分布和剂量体积直方图比较3种不同照射技术的剂量均匀性以及正常组织受量，高剂量区域用受照剂量〉60Gy体积占全体积（V60）百分比比较，执行效率用子野数目和总机器跳数比较。结果3种调强治疗技术的处方剂量均能包括计划靶区（PTV2），但剂量分布存在差别，V60分别为65％、10％和3％。3种技术中脊髓最大受量分别为42．0、48．9和45．1Gy，气管平均剂量分别32．92、52．17和36．56Gy。结论颈部切线野技术方法简单，但下颈部和锁骨上区剂量分布非常不均匀。7野调强技术靶区剂量分布有所改善，但在气管和喉所在区域以及靶区外产生剂量重叠区，脊髓受量也较高。8野调强技术靶区和正常组织剂量分布都明显改善。

Objective To evaluate the absorbed doses of lower-neck and supraclaviclar subclinical target and the normal tissues of nasopharyngeal carcinoma using three different intensity-modulated radiation therapy （IMRT） techniques. Methods Three radiotherapy techniques were single tangential low neck-supraclavicular field technique （techl）, seven portal IMRT in which the gantry angles are 180°, 150°, 120°, 90°, 270°, 210° （tech2） and 240°and eight portal IMRT in which the gantry angles are 180°, 150° 120°, 90°, 0°, 270°, 210°and 240°（tech3）. The dose distribution of lower-neck and supraclaviclar subclinical target and normal tissues were analyzed through the dose-volume histograms, high dose volumes were analyzed using V60 （volume of accepted 〉 60 Gy/all volume x 100% ）. The delivery efficiencies were evaluated by means of the total number of segments and MUs. Results The V60 of PTV2 were 65 %, 10% and 3 % in techl, tech2 and tech3 respectively. The maximum doses of spinal cord were 42.0, 48.9 and 45.1 Gy in techl, tech2 and tech3 respectively. The average doses of trachea were 32.92, 52.17 and 36.56 Gy in techl, tech2 and tech3 respectively. Conclusions Techl is simple method, but the dose distribution is very nonuniform. Tech2 is better than the Techl, but the spinal cord and trachea receive the highest doses in three strategies. Tech3 uses less number of segments and MUs than Tech2, and has the best dose distribution.