鼻咽癌常规放疗中面颈联合野的剂量分布研究

Study of dose distribution of facial-cervical fields in the conventional radiotherapy of nasopharyngeal carcinoma

目的分析鼻咽癌常规放疗中面颈联合野的剂量分布图以了解剂量分布上存在的问题。方法采用美国ADAC公司的Plnnacle治疗计划系统对1例鼻咽癌患者（福州分期为T2N0M0 Ⅱ期）行双侧面颈联合野和中下颈前切野常规定位，再用CT模拟定位机进行CT扫描，把CT影像传送到Plnnacle治疗计划系统进行图像重建及照射野重建，再进行二维计划剂量运算，从而得到各层的剂量分布曲线。结果100％等剂量曲线仅能全包鼻咽腔和蝶窦底壁；105％等刺量曲线全包口咽和射野内的全部颈段脊髓，110％等剂量曲线包口咽的下部分和颈3、4段部分脊髓；95％和90％等剂量曲线穿过蝶窦和斜坡中央；5O％的等剂量曲线与射野各界重叠。两野共线处附近组织位于110％等剂量曲线内，最高剂量达220％。结论面颈联合野剂量分布存在着以下几点缺陷：（1）蝶窦和斜坡均在100％～50％的等剂量曲线之间，故存在颅底和斜坡欠量；（2）口咽部剂量在105％～110％的等剂量曲线之间，为高量区，故放射性咽炎常见；（3）颈段脊髓均位于105％～110％高剂量区，易产生放射性脊髓病；（4）两野共线处出现剂量重叠。

Objective To explore the problems of dose distribution by analyzing the dose distribution graph in the conventional radiotherapy of nasopharygeal carcinoma （NPC）.Methods One patient with NPC was designed on a X-ray simulator with bilateral facial-cervical fields and low neck-supraclavicular field, then by the CT- based simulation and the CT images were transferred to the ADAC Pinnacle treatment planning system to reconstruction. Then the radiation fields were reconstructed and the dose distribution curves were got by the two-dimensional planning dose operation. Results Nasopharygeal cavity and the base wall of sphenoid sinus were within the 100% isodose curve; oropharynx and all cervical spinal segments in the radiation field were within the 105% isodose curve; lower part of oropharynx and 3rd and 4th cervical spinal segments were within the 110% isodose curve; the 95% and the 90% isodose curve were through sphenoid sinus and the center of clivus; the 50% isodose curve was overlapped with the borders of the radiation fields. The tissues adjacent to the overlap were within the 110% isodose curve and the highest dose was 220%. Conclusions The deficiency of dose distribution of facial-cervical fields were： （1） Sphenoid sinus and skull base were within the 100% to 50% isodose curves and these two places were dose deficient. （2） Oropharynx was within the 105% to 110% isodose curves and was within high dose area, so radiopharyngitis happened frequently. （3） Cervical spinal segments were all within the 105% to 110% high dose area , with high rate of radiation myelopathy. （4）There exist dosage overlap at the conjunction of two beams（radiation fields）.