The LET spectra at different penetration depths along secondary⁹C and¹¹C beams

Abstract

Owing to the potentially therapeutic enhancement of delayed particles in treating malignant diseases by radioactive 9C-ion beam, LET spectra at different penetration depths for a 9C beam with 5% momentum spread, produced in the secondary beam line (SBL) at HIMAC, were measured with a multi-wire parallel-plate proportional counter. To compare these LET spectra with those of a therapeutic 12C beam under similar conditions, the 12C beam was replaced with an 11C beam, yielded in the SBL as well and having almost the same range as that of the 9C beam. The LET spectra of the 9C beam and its counterpart, i.e. the 11C beam, at various depths were compared, especially around the Bragg peak regions. The results show that nearby the Bragg peak lower LET components decreased in the LET spectra of the 9C beam while extra components between the LET peak caused by the primary beam and the lower components due to the fragments could be observed. These additional contributions in the LET spectra could be attributed to parts of the emitted particles from the radioactive 9C ions with suitable conditions regarding the LET counter. Integrating these LET spectra in different manners, depth-dose and dose-averaged LET distributions were obtained for the 9C and 11C beams, forming the basic data sets for further studies. In general, the depth-dose distributions of the 9C and 11C beams are comparative, i.e. almost the same peak-to-plateau ratio. The ratio for the 9C beam, however, has room to increase due to the geometric structure limitation of the present detector. The dose-averaged LETs along the beam penetration are always lower for the 9C beam than for the 11C beam except at the falloff region beyond the Bragg peak. Applying the present depth-dose and dose-averaged LET data sets as well as the essential radiobiological parameters obtained with 12C beams previously for HSG cells, an estimate concerning the HSG cell surviving effects along the penetration of the 9C and 11C beams shows that lower survival fractions for the 9C beam at the distal part of the Bragg peak, corresponding to the stopping region of the incoming 9C ions, can be expected when the same entrance dose is given. It is still hard to appreciate the potential of 9C beams in cancer therapy based on the present LET spectrum measurement, but it provides a substantial basis for upcoming radiobiological experiments.

Unraveling the mystery of enhanced cell-killing effect around the Bragg peak region of a double irradiation source 9C-ion beam

“…2, it can be found that the maximum RBE value is beyond the depth of the Bragg peak and coincides with the dose-averaged LET and ion-stopping distributions. This agrees with the theoretical prediction [13] and the experimental measurement [27] in which the maximum of dose-averaged LET is downstream the Bragg peak of depth dose.…”

“…The calculation result shows that the maximum stopping probability density is located at the depth of 148 mm, corresponding to the peak of the RBE values at the depth of 151 mm. Additionally, our previous measurement demonstrated that the maximum of the dose-averaged LET values of the 9 C beam in penetration depth occurred at the depth of about 151 mm [27] . So the resulting cell lethal effect of the 9 C beam is influenced by both of the beam itself and the delayed particles.…”

Depth absorbed dose and LET distributions of therapeutic , , , and beams

“…Various investigations on ion beam radiation quality have been carried out considering the absorbed dose and LET distributions as well as fragmentation processes. 9,[13][14][15][16] The present study focuses on the depth dose and LET distributions of 1 H, 4 He, 7 Li, and 12 C ions in tissuelike media using the Monte Carlo code SHIELD-HIT. 17 The influence of range straggling on the fluence average LET in the Bragg peak region was studied for protons as well as other light ion beams in water.…”

Unraveling the mystery of enhanced cell-killing effect around the Bragg peak region of a double irradiation source9C-ion beam

“…It is clear that the region where the RBE values of the 9 C beam are higher than those of the 12 C beam, i.e. This agrees with the theoretical prediction [13] and the experimental measurement [27] in which the maximum of dose-averaged LET is downstream the Bragg peak of depth dose. We preliminarily conclude that the reason why the 9 C beam showed the enhanced effect at the depths around its Bragg peak is due to the emitted alpha particles and protons from the decays of the stopping 9 C ions.…”