改进鼻咽癌体外放射治疗方法的建议

IMPROVEMENT OF EXTERNAL RADIOTHERAPY FOR NASOPHARYNGEAL CARCINOMA

鼻咽癌放射治疗的5年生存率滞留在40～50％左右,治疗失败的主要原因之一是局部癌复发,复发率约30～40％,多由于放射剂量分布欠理想,靶区内存在着低剂量“冷区”。

The dose distribution patterns of 3 kinds of external radiotherapy currently used for nasopharyngeal carcinoma (NPG) as mapped out by TPS were studied. It was demonstrated that the dose at foramen ovale, posterior portion of the orbit and maxillary siuns were nuderdosed. It was especially marked at the paranasopharyngeal spaces, the ante- and retro- styloid regions. The 3 conventional methods are valid for very early NPG lesions only.For moderately advanced or advanced NPC, we prefer a new method using 2 opposing lateral portals and two 45° oblique retroauricular portals. The dose distribution of this new method is more satisfactory by : 1. having the target volume encompassing the paianasopharyngeal spaces, the ante- and retro-styloid regions in addition to the structures previously cited. 2. setting posterior border of the lateral portal at the posterior border of the axis vertebra in order to increase the dose in the paranasopharyngeal spaces and the ante- and retro- styloid regions, 3. elective use of the anterior nasal portal which is used for very early lesions, and 4.. showing that 60Co was better than g MV-X ray. Therefore, linear accelerators may not be pesistently sought for.