Study and development of two innovative electron beam imaging systems for dosimetry in IORT (intra operative radiation therapy)

Intra operative radiation therapy (IORT) is a technique based on delivery of a high dose of ionising radiation to the cancer tissue, after tumour ablation, during surgery. The major stumbling block to the large-scale application of this radiotherapy technique is the transfer of the patient, with an open wound, from the operating room to the radiation therapy bunker, with the consequent organisational problems and the increased risk of infection. To overcome these limitations, Novac7, a new linear accelerator expressly conceived to perform in the operating room, has been developed. It can deliver electron beams of different energies with a high dose rate (up to 20 Gy/min). These peculiar characteristics give rise to some complications with classical dosimetric techniques. In the framework of a research contract between ENEA and the Physics Department of the University of Bologna, Italy, two original systems have been developed to study and visualise the Novac7 electron beam in real time. The first system is composed by an electron-light converter, a cooled CCD camera and a computer with dedicated software. The second dosimeter is based on a grid of scintillating optical fibres coupled with photodiodes. The achieved results prove that the first system is able to obtain two dimensional measurements of dose distributions in real time and it is a good system for quality controls. The second system has the same capabilities of the first one, but moreover it has the possibility to monitor the delivered beam impulse by impulse. The conclusions confirm the capability of both instruments to overcome problems encountered with classic dosimetry, showing that the results obtained strongly encourage the continuation of this research.