Microdosimetric Evaluation of Secondary Particles in a Phantom Produced by Carbon 290 MeV/nucleon Ions at HIMAC

Abstract

Microdosimetric single event spectra as a function of depth in a phantom for the 290 MeV/nucleon therapeutic carbon beam at HIMAC were measured by using a tissue equivalent proportional counter (TEPC). Two types of geometries were used: one is a fragment particle identification measurement (PID-mode) with time of flight (TOF) method without a backward phantom, and the other is an in-phantom measurement (IPM-mode) with a backward phantom. On the PID-mode geometry, fragments produced by carbon beam in a phantom are identified by the DeltaE-TOF distribution between two scintillation counters positioned up- and down-stream relative to the tissue equivalent proportional counter (TEPC). Lineal energy distributions for carbon and five ion fragments (proton, helium, lithium, beryllium and boron) were obtained in the lineal-energy range of 0.1-1000 keV/microm at eight depths (7.9-147.9 mm) in an acrylic phantom. In the IPM-mode geometry, the total lineal energy distributions measured at eight depths (61.9-322.9 mm) were compared with the distributions in the PID-mode. Both spectra are consistent with each other. This shows that the PID-mode measurement can be discussed as the equivalent of the phantom measurement. The dose distribution of the carbon beam and fragments were obtained separately. In the depth dose curve, the Bragg peak was observed. Relative biological effectiveness (RBE) for the carbon beam in the acrylic phantom was obtained based on a biological response function as a lineal-energy. The RBE of carbon beam had a maximum of 4.5 at the Bragg peak. Downstream of the Bragg peak, the RBE rapidly decreases. The RBE of fragments is dominated by Boron particles around the Bragg peak region.

Estimations of relative biological effectiveness of secondary fragments in carbon ion irradiation of water using CR‐39 plastic detector and microdosimetric kinetic model

“…These clearly separated LET spectra enabled us to calculate RBE with the MK model. In carbon ion therapy, fragments with high atomic number (Z < 6) have potentially high RBE, which should be included for an accurate RBE calculation. Our estimation showed RBEs of 1.6 and 1.3 for 90% and 10% survival fractions at the small angle, respectively.…”

In silico comparison of the dosimetric impacts of a greater omentum spacer for abdominal and pelvic tumors in carbon-ion, proton and photon radiotherapy

“…It is noteworthy that there was no significant difference between C-ion RT and proton RT in reduction of D2 cc of the GI tract by the GO spacer. In general, the distal dose to C-ion RT is considered to be higher than that to proton RT due to the fragmentation tail of C-ions [20, 30, 31]. Also, the lateral dose to C-ion RT has been reported to be lower than that to proton RT [32–34].…”

Effective Dose Measured with a Life Size Human Phantom in a Low Earth Orbit Mission

“…Also, active dosimeter that can tell an astronaut the unexpected exposure to high dose radiation caused by solar particle event is desirable to be developed. Finally, ongoing efforts in the fields of radiation biology and medicine [39][40][41][42] are no doubt important to reduce the large uncertainties associated with the biological effects of the HZE particles and their secondary radiations encountered in space. [43][44][45] …”