Monte Carlo Design, Dosimetry and Radiation Protection Studies for a New Mobile Electron Accelerator for IORT

Intraoperative radiation therapy (IORT) delivers a large, single fraction dose of radiation to a surgically exposed tumor or tumor bed. This presentation reviews the design concept and dosimetry characteristics of an electron beam forming system for an IORT accelerator, with special emphasis on beam flatness, X-ray contamination and protecting personnel from dose delivered outside the treatment field.
The Monte Carlo code, BEAMnrc/EGSnrc, was used to design, verify and optimize the electron beam forming system for two different docking methods with circular metallic applicators. Calculations of therapeutic beam characteristics were performed at the patient surface. Findings were obtained for initially monoenergetic electron beams with an energy range from 4 to 12 MeV, SSD equal to 60 cm., and circular applicators with diameters from 3 to 12 cm. The aim was to build an electron beam forming system (collimators, scattering-flattening foils, applicators ) that is universal for every beam energy and every field diameter described above.
As direct irradiation of surgically exposed organs with an accelerator in a regular operating room raises specific questions concerning radiation safety of the patient and medical personnel, an important aim of this project was to optimize the beam forming system and external shields in order to assure radiation safety. FLUKA code was used to optimize the beam stopper and an optimal configuration of movable shields in the operating room during an IORT procedure.
Two–D distribution of dose equivalents inside and outside the operating room was calculated for a maximum energy of 12 MeV. Dose distribution inside and outside operating room, meets all regulatory requirements for radiation protection. A prototype of mobile electron accelerator is now being constructed for testing in the laboratory.

This project was funded by the Polish Ministry of Science and Higher Education and the EU in frame of Operational Programme – Innovative Economy, project no. POIG 1.1-21