Betatron with variable energy for IORT

Abstract

Introduction Since 2014 years in Tomsk Polytechnic University a new generation of betatrons for intraoperative radiation therapy (IORT) has been developing which has typical diameter approx. 70 cm at 6 MeV energy. The main advantages of the betatrons are that they operate at large frequency (400 Hz) at rather low pulse current, they have low energy spread and the relatively low cost of a device (typically $200,000). Purpose The purpose of the project is to develop and test the compact betatron with adjustable energy of the extracted electron beam. Materials and methods The depth dose distribution was measured along axis using plane-parallel Marcus ionization chamber and Gafchromic EBT-3 polymer film. Dosimetry was carried out following TG-51 and TRS-398 international protocols. The polymer films were calibrated using 10 MeV electron beam of Electa Axcess accelerator and 6 MeV electron beam of previous generation IORT betatron with constant energy. All measurements were performed in tissue-equivalent phantom with zero air gap. Results The investigation of 3D dose distributions generated by new type of IORT source based on betatron was carried out in the energy range 2–6 MeV with 500 keV steps. In addition the radiation background distribution near the betatron was measured and it would be used for design of biological protection. Conclusion According to the measured data it was proved that the extracted electron beam has designed energy that could be changed. The dose distributions allow assume that the compact IORT source based on betatron could be developed in the nearest future.