Technical and Dosimetric Study of Four Facio-cervical Fields Conformal Radiotherapy for Nasopharyngeal Carcinoma

摘要

Purpose: The aim of this study is to establish the methods of four facio-cervical fields' conformal radiotherapy (4F-CRT) for nasopharyngeal carcinoma (NPC), and to optimize the methods for clinical practice. Methods and Materials: Forty patients with untreated NPC of T1 ～ T4 (1997 AJCC Staging System) were rolled into this study. Conventional and four facio-cervical fields conform plans were designed for each patient using Pinnacle 8.0 three-dimension treatment planning system (3D-TPS): 1. Improved plan, four facio-cervical fields' conform plan, anterior , posterior facio-cervical and two lateral opposing facio-cervical fields; and2. Conventional 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. The mean doses of Dmax for brain stem in conventional plan were much lower than those in the improved plan, though both were within safety limits. 3. Compared with the conventional plans, the improved plan significantly decreased the hotspot areas in the target volume and had better parotid glands and temporal mandibular joints sparing effect. Conclusions: Compared with the conventional plan, the improved plan provides satisfactory dose coverage to the tumor volume and better sparing of the parotid gland, TMJs and other normal tissues in external beam radiotherapy of NPC.