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背景与目的:N2-3期鼻咽癌常规照射时,需设置中间挡铅的前切线野照射下颈锁骨上淋巴引流区,目前对于中间铅挡块宽度仍有不同的做法,本研究通过应用三维治疗计划系统(three-dimensional treatment planning system,3D-TPS)对前切线野照射下颈锁骨上区的剂量分布进行分析,探讨合适宽度的铅挡块。方法:选取初治N2-3期鼻咽癌患者10例,采用3D-TPS设计照射方案。每例患者均采用逐步缩野照射技术,下颈锁骨上区均设置单前切线野,前40Gy中间分别采用铅挡0cm(A方案)、2.1cm(B方案)、2.5cm(C方案)、3.0cm(D方案),之后中间均挡3.0cm4种方案。每例患者的4种方案照射剂量均相同。比较4种照射方案的靶区及主要危及器官的受照体积和剂量。结果:(1)4种方案下颈锁骨上亚临床病灶区(PTV50a)的高剂量区覆盖率(V95、V90)比较:A方案(82.44%、87.89%)优于B方案(78.21%、84.03%)、C方案(77.10%、82.68%)、D方案(73.80%、77.50%)(P<0.05);B方案、C方案好于D方案(P<0.05);B方案与C方案比较无统计学意义(P>0.05)。而对于原发灶大体肿瘤区(PTVnx)、颈部转移淋巴结(PTVnd)、原发灶周围高危区(PTVnx60)、转移淋巴结周围高危区(PTVnd60)及环状软骨以上的亚临床病灶区(PTV50b)的V95、V90,4种方案之间比较差异均无统计学意义(P>0.05)。(2)4种方案脊髓、喉的受照剂量无统计学意义;甲状腺、食管、气管的受照剂量(D50):A方案(49.47、44.52、44.18Gy)高于B方案(41.95、8.41、10.16Gy)、C方案(38.73、7.03、8.55Gy)、D方案(26.82、5.63、7.60Gy)(P<0.05);B方案、C方案均高于D方案(P<0.05);B方案、C方案比较无统计学意义(P>0.05)。(3)正常组织并发症发生率(NTCP)的比较:甲状腺的NTCP,A方案(7.9%)高于B方案(4.8%)、C方案(4.3%)、D方案(3.0%)(P<0.05);B方案、C方案均高于D方案(P<0.05);B方案、C方案之间比较无统计学意义(P>0.05)。其余主要危及器官的NTCP,4种方案比较差异无统计学意义(P>0.05)。结论:在不明显增加主要危及器官受照剂量的情况下,A方案有最优的下颈锁骨上区亚临床病灶高剂量区覆盖率,D方案最差;行下颈锁骨上区照射时,我们推荐前40Gy中间不设铅挡块,之后选用个体化铅挡块。对于头颈部摆位误差小的单位,建议采用铅挡块宽度≥2.1cm、≤2.5cm。
BACKGROUND & OBJECTIVE: In the conventional irradiation of N2-3 nasopharyngeal carcinoma, there is still a need for setting the width of the middle lead block in the pre-tangent field of middle lead block under the irradiation of the supraclavicular lymphatic drainage area. In this study, Three-dimensional treatment planning system (3D-TPS) The dose distribution of the supraclavicular region under the anterior tangent field was analyzed to explore the proper width of the lead block. Methods: Ten patients with nasopharyngeal N2-stage nasopharyngeal carcinoma were selected and the irradiation program was designed by 3D-TPS. Each patient was treated with gradual shunting technique. Single anterior tangent field was placed on the lower cervical and supraclavicular regions. The first 40Gy was designed with lead block 0cm (A protocol), 2.1cm (protocol B), 2.5cm (protocol C) 3.0cm (D program), followed by the middle of 3.0cm4 kinds of programs. Each patient’s four programs irradiation dose are the same. The target areas of four irradiation protocols and the irradiated volume and dose of the major organs were compared. Results: (1) Comparison of coverage of high dose area (V95, V90) of subclavian supraclavicular subclavian area (PTV50a) under 4 protocols: A (82.44%, 87.89%) was superior to B (78.21%, 84.03 (P <0.05); B (C), C (77.10%, 82.68%), D (73.80%, 77.50% Statistical significance (P> 0.05). However, PTVnx, PTVnx60, PTVnx60, PTVnd60 and PTV50b were significantly different in primary tumor area (PTVnx), cervical lymph node metastasis (PTVnx60), high metastatic lymph node area There was no significant difference between V95, V90 and 4 protocols (P> 0.05). (2) The doses of spinal cord and larynx were not significantly different among the four regimens. The dose of thyroid, esophagus and trachea was higher than that of regimen B (49.95, 44.52, 44.18Gy) (P <0.05); B regimen, C regimen (38.73,7.03,8.55Gy), D regimen (26.82,5.63,7.60Gy) (P <0.05) C program was not statistically significant (P> 0.05). (3) Comparisons of normal tissue complication rate (NTCP): The thyroid NTCP, A regimen (7.9%) was higher than the B regimen (4.8%), C regimen (4.3%), D regimen (3.0% 0.05). There was no significant difference between B and C regimens (P> 0.05). There were no significant differences among the other four schemes (P> 0.05). CONCLUSION: Under the condition of no significant increase of dose of the organ at the main end, the optimal coverage of subclinical hypofractionation in the subclavian supraclavicular region is highest in scheme A, and scheme D is the worst. In the case of irradiation on the supraclavicular area, We recommend the middle of the first 40Gy no lead stopper, after the selection of individual lead stopper. For units with small head and neck positioning error, it is recommended to use lead stopper width ≥2.1cm, ≤2.5cm.