Parallel-plate chambers as radiation-hard detectors for time-based beam diagnostics in carbon-ion radiotherapy

TL;DR

This study demonstrates that parallel-plate ionization chambers can provide real-time, high-precision range and energy verification for carbon-ion beams, enhancing safety and accuracy in radiotherapy.

Contribution

The paper introduces a novel application of parallel-plate chambers with CO₂ gas for real-time, picosecond-precision beam diagnostics in carbon-ion radiotherapy.

Findings

Timing precision approaching one picosecond.

Range uncertainty of approximately 1 mm.

Beam energy determination within 1 MeV/nucleon.

Abstract

Accurate range verification of carbon ion beams is critical for the precision and safety of charged particle radiotherapy. In this study, we evaluated the feasibility of using a parallel-plate ionization chamber for real-time, time-based diagnostic monitoring of carbon ion beams. The chamber featured a 0.4 mm gas gap defined by metallic electrodes and was filled with carbon dioxide (CO$_2$), a non-polymerizing gas suitable for high-rate applications. Timing precision was assessed via self-correlation analysis, yielding a precision approaching one picosecond for one-second acquisitions under clinically relevant beam conditions. This level of timing accuracy translates to a water-equivalent range uncertainty of approximately 1 mm, which meets the recommended clinical tolerance for carbon ion therapy. Furthermore, the kinetic energy of the beam at the synchrotron extraction point was determined from the measured orbital period, with results consistently within 1 MeV/nucleon of the nominal energy. These findings demonstrate the potential of parallel-plate chambers for precise, real-time energy and range verification in clinical carbon ion beam quality assurance.