Speaker
Description
Radiation therapy with carbon ions is characterized by high biological effectiveness due to the high Linear Energy Transfer (LET) of both primary ions and the secondary fragments produced along the beam path. In clinical practice, RBE calculations are typically based on radiobiological models which links microscopic energy deposition patterns to cellular response. Microdosimetry provides useful tools to characterize the complex mixed radiation fields generated by carbon ions by describing the stochastic energy deposition at the micrometric scale which can be linked to the biological response.
In this work, microdosimetric measurements were performed at the italian National Centre of Oncological Hadrontherapy (CNAO) using a silicon telescope composed of a micrometric ΔE stage coupled to a residual-energy E detector. The ΔE stage operates as a microdosimeter, while the E stage enables particle identification and discrimination.
Microdosimetric spectra were acquired in-field, in lateral out-of-field regions, and beyond the Bragg peak. The measurements revealed a substantial contribution of light fragments (protons, helium ions, and intermediate mass fragments) in distal and lateral regions. The lineal energy distributions exhibited a pronounced increase in high LET components near the Bragg peak, associated with slow carbon ions and fragments. High LET contributions were observed outside the primary field due to fragmentation and scattering processes. The dose-mean lineal energy showed strong spatial variation correlated with depth and fragments distribution.
RBE was estimated from the measured microdosimetric spectra using biologically weighted approaches like the Microdosimetric Kinetic Model. The results indicate a marked increase in RBE in the Bragg peak and distal regions, together with non-negligible biological effectiveness in lateral out-of-field areas attributable to high-LET fragments.
These findings demonstrate the capability of silicon-based microdosimetry to characterize carbon-ion radiation fields and provide input for variable RBE modeling, contributing to improved assessment of biological dose both inside and outside the target volume.