Kilovoltage rotational radiotherapy of breast cancer with the BriXS source

Kilovoltage rotational radiotherapy of breast cancer has been proposed as an alternative procedure to the conventional breast radiotherapy with 6 MeV photon beams. The use of orthovolt- age X-ray tubes rotating around the breast, instead of conventional medical linear accelerators, would allow for significant reduction of acquisition and management costs. However, the employment of an X-ray tube limits the maximum available photon flux: a synchrotron radiation source could provide a high dose rate, but its clinical use is prevented by the size of such a source. In this work, we propose the use of the BriXS twin Compton pulsed X-ray source as a compact alternative to the synchrotron radiation source, for kilovoltage radiotherapy of breast cancer. This proposed source presents a footprint of 40 m × 20 m, and the X-ray spectrum presents a mean energy of 88 keV with a suitable photon flux. The dose distribution in a simulated radiotherapy session was computed via a Monte Carlo software based on the Geant4 simulation toolkit. The study focused on the skin dose ratio, i.e. the percent ratio between the dose to the skin and that to the tumor volume in the modelled breast. A low skin dose allows for a suitable sparing of skin tissue during radiotherapy. For a cylindrical model breast with a diameter of 140 mm embedding a spherical simulated lesion with a diameter of 10 mm placed at the rotational axis of the cylinder, the calculated skin-to-tumor dose ratio was as low as 7%.