Investigation of the track structure of therapeutic carbon ion radiation using PTB’s nanodosimeter

As part of a joint project realized in collaboration with the Heidelberg Ion‑Beam Therapy Center (HIT), the track structure of carbon ions of therapeutic energy was investigated after they had penetrated a layer of simulated tissue. For this purpose, the ionization cluster size distribution (ICSD) was measured in several beam times using PTB’s nanodosimeter. A PMMA absorber, which simulated the layer of tissue, was irradiated with carbon ions of an energy of 3.5 GeV (292 MeV/u). When the carbon ions enter the vacuum chamber of the nanodosimeter, their energy level has decreased. The generated mixed radiation field contains not only the primary carbon ions but also all of the secondaries (ions and electrons) and fragments (generated during the penetration of the simulated tissue). The following parameters were investigated during the beam times:

-      reproducibility of the ICSD measurements

-      influence of the entrance window on the ICSD measurements

-      influence of the front PSD on the ICSD measurements

-      influence of the PMMA absorber thickness (= simulated tissue depth) on the ICSD measurements at a constant energy of the primary carbon ions

Another beam time is planned to investigate the influence of the combined variation of the PMMA absorber thickness and the carbon ion energy on the ICSD measurements, with the constraint that the carbon ion energy remains constant in the nanodosimeter’s target volume.

The objective of the measurements was to prove that the developed measuring system can be used in ion radiation therapy. Once the planned measurements have been completed, the system can be made available to interested users.

Contact

G. Hilgers, Department 6.3, Working Group 6.31