Intra Operative Radiation Therapy (I.O.R.T.) is a special radiotherapy technique based on delivery of a single high dose of ionising radiation to the cancerous tissue during oncological surgery.  Novac7, a new kind of linear accelerator (manufactured by Hitesys), has been expressly conceived for direct use in the surgical room. Novac7 can deliver electron beams of different energies (3, 5, 7 and 9 MeV), with a high dose rate (up to 20 Gy/minute).  These peculiar characteristics give rise to some complications with classical dosimetric techniques. 
The aim of this work, funded by ENEA in the framework of a research contract, is the development of an innovative system for real time measurements of 2D dose distributions and electron beam characterisation, before radiotherapy treatment with Novac7.

THE ACQUISITION LINE 

The detector is entirely contained in an aluminium box, without light loss and is made up of the following components: 
- a scintillator (150x150 mm2) which “converts” electrons into light, 
- a camera with a Peltier cooled CCD sensor (768x512 pixel, 9x9 mm2 each), 
- a 45° mirror. 

The light produced within the converter is reflected by the mirror and is focalised on the CCD sensor by a large angle lens. 

SPIKES CORRECTION 

A stochastic noise is present within the images and it is probably caused by bremsstrahlung radiation, which have a direct interaction with the CCD chip. This results in large signals in isolated pixels (“spikes”). We have developed a software, using ad hoc studied filters, able to eliminate it almost completely. Figures right: a beam image and its profile before and after software correction. 

SYSTEM ANALYSIS 

System response as a function of pulse number, with different converters: 
- a BC-430 plastic scintillator, 
- a Gd2O2S:Tb screen, 
- a ZnS converter. 

SYSTEM ANALYSIS 

System response as a function of beam energy, with BC-430 converter.