Towards breast cancer rotational radiotherapy with synchrotron radiation

We performed the first investigations, via measurements and Monte Carlo simulations on phantoms, of the feasibility of a new technique for synchrotron radiation rotational radiotherapy for breast cancer (SR³T).

A Monte Carlo (MC) code based on Geant4 toolkit was developed in order to simulate the irradiation with the SR³T technique and to evaluate the skin sparing effect in terms of centre-to-periphery dose ratio at different energies in the range 60-175keV. Preliminary measurements were performed at the Australian Synchrotron facility. Radial dose profiles in a 14-cm diameter polyethylene phantom were measured with a 100-mm pencil ionization chamber for different beam sizes and compared with the results of MC simulations. Finally, the dose painting feasibility was demonstrated with measurements with EBT3 radiochromic films in a phantom and collimating the SR beam at 1.5cm in the horizontal direction.

MC simulations showed that the SR³T technique assures a tumour-to-skin absorbed dose ratio from about 7:1 (at 60keV photon energy) to about 10:1 (at 175keV), sufficient for skin sparing during radiotherapy. The comparison between the results of MC simulations and measurements showed an agreement within 5%. Two off-centre foci were irradiated shifting the rotation centre in the horizontal direction.

The SR³T technique permits to obtain different dose distributions in the target with multiple rotations and can be guided via synchrotron radiation breast computed tomography imaging, in propagation based phase-contrast conditions. Use of contrast agents like iodinated solutions or gold nanoparticles for dose enhancement (DE-SR³T) is foreseen and will be investigated in future work.