Real-Time System 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, while reducing the exposure of normal surrounding tissue. The Novac7 is a new linear accelerator expressly conceived to perform in the operating room. This accelerator supplies electron beams with high dose rate. Because these peculiar characteristics, classical dosimetric techniques are not able to give at once a real-time response and an extensive measure of the absorbed dose. The new system is composed by a grid of scintillating optical fibres coupled with two arrays of photodiodes. The instrument samples the delivered beam at 100 Hz. The dedicated software collects the two projection-signals and reconstructs the bi-dimensional image. Moreover it provides a series of dosimetric parameters. We studied an appropriate reconstruction algorithm searching the best compromise between the computational complexity and an high precision. An accelerator having energies ranging from 3 to 12 MeV has been used for the tests. The system is able to give a real time response (within 30 seconds), the resolution is of 1 millimeter. The response is linear versus dose and the measures are not affected by the high dose rate. The conclusions confirm the capability of the instrument to overcome problems encountered with classic dosimetry, showing that the results obtained strongly encourage the continuation of this research.