MICRODOSIMETRIC STUDY AT THE CNAO ACTIVE-SCANNING CARBON-ION BEAM

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Instrumentation

Background:

• The Italian National Centre for Oncological Hadrontherapy (CNAO) utilizes carbon-ion beams with active-scanning for cancer treatment since 2011.
• This modality involves high particle-fluence rates (>10^5 s^-1 mm^-2) and narrow Bragg peaks (~1 mm FWHM).
• Commercial tissue-equivalent proportional counters (TEPCs) are often too large for accurate measurements under these conditions.

Purpose of the Study:

• To develop and evaluate novel, smaller detectors for microdosimetric measurements in high-fluence carbon-ion therapy beams.
• To assess the capability of home-made detectors in characterizing microdosimetric spectra at CNAO.
• To compare measurements from different detector types in a therapeutic carbon-ion beam.

Main Methods:

• Utilized two custom-built detectors: a mini tissue-equivalent proportional counter (mini-TEPC) with a 0.81 mm^2 sensitive area and a silicon telescope with a 0.125 mm^2 sensitive area.
• Performed measurements using a monoenergetic carbon-ion beam (189.5 ± 0.3 MeV/u) at CNAO, scanning a 3 × 3 cm^2 treatment area.
• Analyzed microdosimetric spectra and calculated mean microdosimetric values.

Main Results:

• Spectral differences were observed in the low y-value region between the detectors.
• Mean microdosimetric values obtained from both detectors were found to be consistent.
• Microdosimetric spectra in the high y-value region were also consistent across the tested detectors.

Conclusions:

• Home-made mini-TEPC and silicon telescope detectors are suitable for microdosimetric measurements in high-fluence therapeutic carbon-ion beams.
• These detectors provide consistent results, particularly in the high y-value region, crucial for understanding radiation effects.
• The developed detectors overcome limitations of commercial instruments, enabling more precise characterization of particle therapy beams.