鼻咽癌常规外照射改进方案的剂量学研究

Dosimetric improvement of external beam radiotherapy for nasopharyngeal Carcinoma

目的 应用三维治疗计划系统 ( 3DTPS)对鼻咽癌常规外照射改进方案进行剂量学研究 ,探讨其临床使用价值。方法 选取初治鼻咽癌患者 8例 ,采用 3DTPS设计照射方案。每例患者均设计 2个方案 :( 1)以鼻前面颈野和双侧面颈联合野为主的常规外照射方案 (改进方案 ) ;( 2 )以双侧面颈联合野为主的常规外照射方案 (传统方案 )。每例患者的 2个方案照射剂量相同。采用剂量体积直方图比较各期鼻咽癌以两种方案照射时靶区、脑干、脊髓、腮腺及颞颌关节的受照体积和剂量。结果 ( 1)改进方案可满足鼻咽和颈部计划靶体积的剂量要求。 ( 2 )两种方案脊髓受照剂量无差异 ;对 5 %和 10 %体积脑干平均受照剂量 (D5、D10 ) ,T1～T3期患者改进方案高于传统方案 (P <0 .0 5 ) ,T4期患者两种方案无差异。 ( 3)改进方案双侧腮腺和颞颌关节受照剂量、分割剂量和被高剂量覆盖的体积均明显低于传统方案 (P <0 .0 1) ,其他正常组织被较高剂量覆盖的体积亦明显小于传统方案 (P <0 .0 1)。结论 与传统方案比较 ,改进方案靶体积在获得满意的剂量覆盖同时 ,可更好地保护腮腺。

Objective To evaluate the dosimetric improvement of conventional external beam radiotherapy for nasopharyngeal carcinoma (NPC) using three-dimensional treatment planning system (3DTPS), and the value in clinical practice. Methods Eight patients with untreated NPC of T1～T4N0～N1M0 (1992 Fuzhou Staging System) were selected into this study. Traditional and improved external beam plans were designed for each patient using 3DTPS: 1. Improved plan, anterior facio-cervical and two lateral opposing facio-cervical fields; and 2. Traditional plan, two lateral opposing facio-cervical fields only with the same dose delivered to the target in each plan, dose volume histograms (DVHs) of the targets and normal organs[brain stem, spinal cord, parotid glands, and temporal mandibular joints (TMJs)] were compared and the dose distribution were evaluated. Results 1. The dose distribution of the improved plan could meet the requirements for the target volume. 2. There was not any significant difference in the dose of spinal cord between the two plans (P>0.05). The mean dose of D5 and D10 for brain stem in traditional plan were much lower than those in the improved plan for T1-T3 patients (P<0.05), though both were within safety limits, but it was not significantly different for the T4 patients (P>0.05). 3. Compared with the conventional plans, the improved plan significantly decreased the hot-spot areas in the target volume and had better parotid glands and temporal mandibular joints sparing effect(P<0.01).Conclusions Compared with the conventional plan, the improved plan provides satisfactory dose coverage to the target volume and better sparing of the parotid gland, TMJs and other normal tissues in external beam radiotherapy of NPC.