Modifications of human voxel models used for radiation protection calculations

Abstract

Aim

The alteration of an already existing voxel model, after the completion of its segmentation, is a complicated process, leading to many problems to be solved. To solve those intricacies in an easy way, a new software tool was developed and shall be presented here.

In the voxel model, organs are represented by voxels (3d-pixels). If the organs are modified, no bit of tissue, i.e. voxel, may vanish nor an extra one should appear. That means organs cannot be modified without considering the neighbouring tissue. Thus, the principle of organ modification is based on the reassignment of voxels from one organ/tissue to another; deleting and adding voxels is only possible at the external surface, i.e. skin. The modifications are done by semiautomatic routines but including human control. Because of the complexity of the matter, a person has to validate that the applied changes on organs are still anatomically reasonable. A graphical user interface was designed to fulfil the purpose of a comfortable working process and an adequate graphical display of the modified voxel model was developed.

With the presented tool, called “VolumeChange”, two human models were adjusted to fit the reference organ masses of a male and a female adult, as defined by the International Commission on Radiological Protection (ICRP). These two new voxel models of the adult male and female reference person are going to succeed the MIRD-type models, which have been used for dosimetry purposes until now.

Single organs, organ complexes and even whole limbs can be edited with respect to volume, shape and location. The new software tool cannot only be used to adjust a voxel model to reference organ masses but also to fit individual patient characteristics. This introduces an important step towards individual patient dosimetry.