直线加速器放射外科剂量分布的数学模型探讨

A STUDY OF THE MATHEMATICAL MODEL ON THE DOSE DISTRILUTIONS OF LINAC-BASED RADIOSURGERY

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。作者认为，靶区中心剂量最高，沿辐射方向大致按正态分布曲线以指数级递减，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。最大剂量梯度处位于５０％～８０％水平之间．该处至靶区中心的距离是临床选择准直仪孔径的重要标准．准直仪孔径越大，照射的弧度越小，则剂量分布越差，对瘤周正常脑组织的危胁也就越大。剂量分布的数学模型是指导放射外科剂量设计的良好方法。

A mathematical model was found on the doses measured in an anthropomorphc phantom dur-ing the LINAC-based radiosugery irradiations,Resulting dose' distributions were studied by model calcula-tions.The highest doses were delivered to the targets. The dose decreases with leaving the target,and the dose fall off profiles appear nomorl distribution.the dose decreases slowly near the target forming high doselevels in the target areas,and then decreases in very deep gradients,which could coincide with the rnargins oftreatment areas,and consequeatly decreases slowly in the low dose levels in the nomal tissue.The greatestgradients were found to be between 50%and 80%isodose levels.The displacements of the greatest gradientpoints from the target centers could be used to chose the optimum collimator sizes.The larger the collimatorsize is and the fewer the irradiation arcs are,the worse the dose distribution will be and the rnore easily thebrain tissue around the tumor will be involved.The mathematical model was an important tool to guide clini- cal dose planning.