Measurements of linear energy transfer (LET) distributions by CR-39 for a therapeutic carbon ion beam with a new 2D ripple filter

This study aims to measure the linear energy transfer (LET) spectra of therapeutic carbon ion beams with a new 2D 6 mm thick ripple filter (RiFi) by using a CR-39 detector. A water phantom was irradiated by three different single energy carbon beams (86.2 MeV/u, 276.5 MeV/u, and 430.0 MeV/u) at Shanghai Proton and Heavy Ion Center (SPHIC), CR-39 detectors were used to measure the LET spectra with and without the RiFi. The Monte Carlo toolkit Geant4 was employed to perform the simulations. The dose-averaged LET (LETd) was calculated according to the LET spectra. The results showed that the 2D RiFi broadens the Bragg peak width and LETd distribution. The simulation LET spectra of primary carbon ions were in good agreement with the experimental results. The LETd can be well estimated by using the measured LET spectra. This result indicated that the RiFi affects the depth-dose distribution and the shape of LET spectra for mono-energetic carbon beams. The CR-39 detector is suitable for LET spectra measurement. It is hoped that this work could provide a new reference method for the cross-validation of basic data in carbon ion clinical quality assurance and benefit clinical treatment.