Stavrev P V, Stavreva N A, Round W H
Department of Physics, University of Waikato, Hamilton, New Zealand.
Australas Phys Eng Sci Med. 1997 Mar;20(1):4-10.
An objective function analysis when target volumes are deliberately enlarged to account for tumour mobility and consecutive uncertainty in the tumour position in external beam radiotherapy has been carried out. The dose distribution inside the tumour is assumed to have logarithmic dependence on the tumour cell density which assures an iso-local tumour control probability. The normal tissue immediately surrounding the tumour is irradiated homogeneously at a dose level equal to the dose D(R) delivered at the edge of the tumour. The normal tissue in the high dose field is modelled as being organized in identical functional subunits (FSUs) composed of a relatively large number of cells. Two types of organs--having serial and parallel architecture are considered. Implicit averaging over intrapatient normal tissue radiosensitivity variations is done. A function describing the normal tissue survival probability S0 is constructed. The objective function is given as a product of the total tumour control probability (TCP) and the normal tissue survival probability S0. The values of the dose D(R) which result in a maximum of the objective function are obtained for different combinations of tumour and normal tissue parameters, such as tumour and normal tissue radiosensitivities, number of cells constituting a normal tissue functional unit, total number of normal cells under high dose (D(R)) exposure and functional reserve for organs having parallel architecture. The corresponding TCP and S0 values are computed and discussed.
针对外照射放疗中为考虑肿瘤移动性和肿瘤位置的连续不确定性而故意扩大靶区体积的情况，进行了目标函数分析。假设肿瘤内部的剂量分布与肿瘤细胞密度呈对数依赖关系，以确保肿瘤局部控制概率相同。紧邻肿瘤的正常组织以等于肿瘤边缘处剂量D(R)的剂量水平进行均匀照射。高剂量场中的正常组织被建模为由相对大量细胞组成的相同功能亚单位（FSU）。考虑了具有串联和平行结构的两种类型的器官。对患者体内正常组织放射敏感性变化进行了隐式平均。构建了描述正常组织存活概率S0的函数。目标函数表示为总肿瘤控制概率（TCP）与正常组织存活概率S0的乘积。针对肿瘤和正常组织参数的不同组合，如肿瘤和正常组织放射敏感性、构成正常组织功能单位的细胞数量、高剂量（D(R)）照射下的正常细胞总数以及具有平行结构器官的功能储备，获得了使目标函数最大化的剂量D(R)值。计算并讨论了相应的TCP和S0值。
