用最小二乘法探讨放射外科剂量分布的规律

A STUDY OF THE MATHEMATICAL MODEL ON THE DOSE DISTRIBUTIONS OF LINAC—BASED RADIOSORGERY

将直线加速器放射外科照射中测得的吸收剂量建立数学模型,探讨剂量分布的规律性,对指导临床应用有重要的作用。作者认为,靶区中心剂量最高,沿辐射方向大致按指效级递减,先缓慢递减,以维持靶区高剂量,再较快递减,形成治疗区边缘,再在低剂量水平缓慢递减,治疗区边缘的大小与准直仪孔径大小及照射方式有关。

A mathematical model was found on the doses measured in an anthropomorphic phantom during the LINAC—based radiosurgery irradiations. Resutting close distributions were studied by model calculations. The highest doses were delivered to the targets. The dose decreases wirh leaving the target, and the dose fall off profiles appear nomorl distribution. The dose decreases slowly near the target forming high dose levels in the target areas, and then decreases in very deep gradients, which could coincide with the margins of treatrment areas, and consequently decreases slowly in the low dose levels in the normal tissue. The greatest gradients were found to be between 50% and 80% isodose levels. The displacements of the greatest gradient points from the target centers could be used to chose the optimum collimator sizes. The larger the collimator size is and the fewer the irradiation arcs. are, the worse the dose distribution will he and the more easily the brain tissue around the tumor will be involved. The mathematical model was an important tool to guide dinical close planning.