A website for voxel dosimetry: Free databases and on-line calculations of voxel S values

Objectives Voxel dosimetry can be defined as the calculation of radiation absorbed dose to tissue regions with dimensions ranging from hundreds of micrometers to a few centimeters. Voxel dosimetry is based on activity quantification with tomographic imaging or autoradiographic techniques, and is of particular interest in radionuclide targeted therapy applications. The voxel cumulative activity can be derived from SPECT or PET, and tissue inhomogeneities from CT. By using this approach, the activity and dose distributions can be determined at the maximal experimental resolution of the radiotracer distribution. Direct radiation transport simulation with Monte Carlo (MC) codes can account for non-uniform source and density distribution, whereas convolution calculation with voxel S values is based on the hypothesis of uniform density distribution. The latter approach cannot account for non-uniform tissue density distribution, but it could result more suitable for most of the clinical physicists, as the MC codes are not always available in clinical settings. Nevertheless, the use of voxel S values has been limited because of the lack of data for different voxel dimensions and radionuclides.

Methods To encourage the spread of this method, a web site has been instituted. Tabulations of voxel S values calculated with MC codes are now available for different voxel dimensions and radionuclides of interest.

Results MC data underwent a severe accuracy control, whose results are reported in the present study.

Conclusions Further work in progress consists to the calculation of S values at the voxel level with convolution of dose point kernels, by means of an on-line software providing real time results for any voxel dimensions