Direct Comparison between Protons and Alpha-particles of the Same LET: I. Irradiation Methods and Inactivation of Asynchronous V79, HeLa and C3H 10T½ Cells

TLDR

Proton effectiveness rises sharply between 17–30 keV µm⁻¹, whereas α‑particles peak above 100 keV µm⁻¹, highlighting LET‑dependent differences in biological impact. The study directly compares the biological effectiveness of protons and α‑particles at identical LETs across multiple in vitro cell systems. Cell monolayers were irradiated with 1.2 and 1.4 MeV protons and 30 and 35 MeV α‑particles, each delivering 23 and 20 keV µm⁻¹ LETs, respectively. In V79‑4 cells the dose‑response linear term for protons exceeded that for α‑particles, a pattern also seen in HeLa and HeLa S3 cells but not in C3H 10T½; these findings agree with Belli et al.

Abstract

AbstractA direct comparison was carried out of the biological effectiveness of protons and α-particles of the same linear energy transfer (LET) under identical conditions with a variety of in vitro biologial systems. Monolayers of mammalian cells were irradiated with accelerated beams of protons (1·2 and 1·4 MeV) and α-particles (30 and 35 MeV) corresponding to LETs of 23 and 20 keV µm−1 for each particle type. For V79-4 cells it was observed that the linear term of the dose-response for cell inactivation by protons was significantly greater than that for α-particles of the same LET. For HeLa and HeLa S3 cells, also, the linear term appeared to be greater for protons, but this was not observed with more limited data for C3H 10T½ cells. The result for V79 cells is in agreement with the report of Belli et al. (1989) who observed that the biological effectiveness of protons rose sharply between 17 and 30 keV µm−1 in strong contrast to α-particles which reached a peak effectiveness at > 100 keV µm−1. These results place new constraints on the biologically relevant features of the microscopic structure of radiation tracks, and have implications for the mechanistic and practical comparison between radiations.