Development and characterization of a 2D scintillation detector for quality assurance in scanned carbon ion beams

• At the CNAO Foundation a scintillating dosimetry system has been developed for beam QA.
• The detector response was tested for the first time for carbon ion pencil beams.
• The system was preliminary characterized in terms of response linearity, reproducibility and homogeneity.
• The detector performances were evaluated by performing a cross-check with reference radiochromic films.
• The results showed that the scintillation detector is suitable for relative 2D dosimetry.

At the Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), a two-dimensional high resolution scintillating dosimetry system has been developed and tested for daily Quality Assurance measurements (QA) in carbon ion radiotherapy with active scanning technique, for both single pencil beams and scanned fields produced by a synchrotron accelerator.The detector consists of a thin plane organic scintillator (25×25 cm2, 2 mm thick) coupled with a high spatial resolution CCD camera (0.25 mm) in a light-tight box.A dedicated Labview software was developed for image acquisition triggered with the beam extraction, data post-processing and analysis. The scintillator system was preliminary characterized in terms of short-term reproducibility (found to be within±0.5%), linearity with the number of particles (linear fit χ2=0.996χ2=0.996) and dependence on particle flux (measured to be <1.5%<1.5%).The detector was then tested for single beam spot measurements (Full Width at Half Maximum and position) and for 6×6 cm2 reference scanned field (determination of homogeneity) for carbon ions with energy from 115 MeV/u up to 400 MeV/u. No major differences in the investigated beam parameters measured with scintillator system and the radiochromic EBT3 reference films were observed. The system allows therefore real-time monitoring of the carbon ion beam relevant parameters, with a significant daily time saving with respect to films currently used.The results of this study show the suitability of the scintillation detector for daily QA in a carbon ion facility with an active beam delivery system.