Medical physics: Radiation Dosimetry at Cellular Level

Researchers: P. Välimäki*, J. Lampinen*, S. Ilvonen1 A. Kuronen*, S. Savolainen*
and J. Stepanek2
*Helsinki University Central Hospital, Finland
1Electromagnetics Laboratory, HUT
2University 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. We have developed a method based on mechanical hard-sphere collisions to build densely packed cell cluster models consisting of a tumor surrounded by healthy cells. The results show that the interface between the tumor cells and healthy cells is more densely packed by the optimization method as compared to the conventional model of cubic close-packed structure. Assuming that the activity is concentrated in the tumor cells and that the radiation components of the activity have short ranges – as is often the case in radioimmuno and neutron capture therapies – the calculated absorbed dose of the healthy tissue depends strongly on the cell model used in the calculations.

In order to take into account the variability of sizes and shapes of the cells, a cell cluster model based on real tissue data from confocal fluorescence microscope images is currently under development.

Figure 37a Figure 37b

Figure 37: 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.