Department of Medical Radiation Physics, Clinical Sciences-Lund, Lund University, Sweden.
Acta Oncol. 2011 Aug;50(6):973-80. doi: 10.3109/0284186X.2011.582517.
Clinical treatment with radionuclides is usually preceded by biokinetic and dosimetry studies in small animals. Evaluation of the therapeutic efficacy is essential and must rely on accurate dosimetry, which in turn must be based on a realistic geometrical model that properly describes the transport of radiation. It is also important to include the source distribution in the dosimetry calculations. Tumours are often implanted subcutaneously in animals, constituting an important additional source of radiation that often is not considered in the dosimetry models. The aims of this study were to calculate S values of the mouse, and determine the absorbed dose contribution to and from subcutaneous tumours inoculated at four different locations.
The Moby computer program generates a three dimensional (3D) voxel-based phantom. Tumours were modelled as half-spheres on the body surface, and the radius was varied to study different tumour masses. The phantoms were used as input for Monte Carlo simulations of absorbed fractions and S factors with the radiation transport code MCNPX 2.6f. Calculations were performed for monoenergetic photons and electrons, and the radionuclides (125)I, (131)I, (111)In, (177)Lu and (90)Y.
Electron energy and tumour size are important for both self- and cross-doses. If the activity is non-uniformly distributed within the body, the position of the tumour must be considered in order to calculate the tumour absorbed dose accurately. If the uptake in the tumour is high compared with that in adjacent organs the absorbed dose contribution to organs from the tumour cannot be neglected.
In order to perform accurate tumour dosimetry in mouse models it is necessary to take the additional contribution from the activity distribution within the body of the mouse into account. This may be of significance in the interpretation of radiobiological tumour response in pre-clinical studies.
临床治疗中通常会先在小动物身上进行生物动力学和剂量学研究。评估治疗效果至关重要，必须依赖准确的剂量学，而准确的剂量学又必须基于能够准确描述辐射传输的现实几何模型。在剂量计算中纳入源分布也很重要。肿瘤通常被皮下植入动物体内，构成了辐射的重要附加源，而在剂量学模型中往往没有考虑到这一点。本研究的目的是计算小鼠的 S 值，并确定来自四个不同位置皮下肿瘤的吸收剂量贡献。
Moby 计算机程序生成一个三维（3D）体素化体模。肿瘤在体表被建模为半球体，半径变化以研究不同的肿瘤质量。将体模用作蒙特卡罗模拟吸收分数和 S 因子的输入，使用辐射传输代码 MCNPX 2.6f。对单能光子和电子以及放射性核素（125）I、（131）I、（111）In、（177）Lu 和（90）Y 进行了计算。
电子能量和肿瘤大小对自剂量和交叉剂量都很重要。如果体内的放射性活度分布不均匀，为了准确计算肿瘤吸收剂量，必须考虑肿瘤的位置。如果肿瘤的摄取量与相邻器官相比较高，则不能忽略肿瘤对器官的吸收剂量贡献。
为了在小鼠模型中进行准确的肿瘤剂量学，有必要考虑到小鼠体内放射性活度分布的额外贡献。这在解释临床前研究中的放射生物学肿瘤反应可能具有重要意义。
