鼻咽腔对其内表面剂量分布的影响

CAVITY EFFECT IN THE DOSE DISTRIBUTION ON THE INNER SURFACE OF NASOPHARYNX

用灵敏层厚度为25μm的GR-200F LiF(Mg,Gu,P)TL测量膜片,在组织等效Mix-D人体头、颈、肩模型内相应位置处,模拟鼻咽部空气腔。结果表明:1.对于8MV-X线和^(60)Co的同轴对穿照射野,气腔6个内表面的剂量分布是均匀的;2.每个壁面和6个壁面平均值之间的相对剂量偏差小于5％;3.由于射线出入气腔内表面的建成和跌落效应对剂量分布的影响不太大。因此,在此种条件的临床实践中可忽略鼻咽腔对剂量分布的影响。

A skin dosimeter of thin film GR200 F LiF(Mg,Cu,p) TL with sensitive layer of about 25 um thick was used. A head, neck and shoulder human phantom of tissue equivalent Mix-D was used for the measurements. A nasopharyngeal cavity of 2.5×3×4 cm was made in the reference position of the phantom to simulate the human organ anatomically. The experimental results showed that: 1. The dose distribution on the six inner surfaces of the air cavity was uniform for the two coaxial-opposing irra- diation fields of 8 MV-X and 60Co rays, 2. The relative dose diversities of the average dose between each wall surface and six wall surfaces were less than 5%, 3. The dose distributions on the exit and incident surfaces due to the 'build-down'and 'building-up'through the interfaces varied little. It is concluded that the influence of the nasopharyngeal cavity on the dose distribution is negligible in clinical practice.