Medical Physics: Radiation Dosimetry at Cellular Level

Researchers: P. Välimäki1, A. Kuronen, S. Savolainen1
and J. Stepanek2
1Helsinki University Central Hospital, Finland
2 University of Zurich and Paul Scherrer Institute, Switzerland

New promising methods in cancer treatment like radioimmuno and neutron capture therapies provide new challenges to dosimetry. Contrary to the therapies exploiting external beam, radiation distributions in these new methods are generally highly non-uniform. Since there exists at the moment no means to measure the doses absorbed by the patients from internally deposited radionuclides, the only way to proceed is to develop theoretical methods to estimate these doses.

One remarkable, but mostly disregarded factor in analytical microdosimetry is the cell cluster model to which the dosimetric calculation itself is applied. Three dimensional cell cluster models have so far been quite simple consisting mainly of clusters of spheres largely due to insufficient computing capacity. On the other hand the cell-level dosimetry field has lacked totally the verification of the cluster models against biological reality. We are currently developing a new method to overcome both of these deficiencies. As the basis for the modelling the method uses realistic cell related microscopy data of the tissues. Dose calculations in the realistic cell cluster makes it possible to verify the usefulness of the currently used cell cluster models and to further estimate the effects of the cell shape, the cell size variation and the spatial distribution of the cells in the cell-level dosimetry.

Figure 34a Figure 34b

Figure 34: Cell models used in cell-level dosimetry. On the left: Cross section of a cell cluster based on the simple cubic close-packed structure. On the right: Cross section of the model created using the optimization method. Red spheres are the smaller tumor cells and green spheres denote the larger healthy cell surrounding the tumor.