Gastrointestinal (GI) cancer risk among astronauts after encountering galactic cosmic radiation (GCR) is predicted to exceed safe permissible limits in long duration deep-space missions. Current predictions are based on relative biological effectiveness (RBE) values derived from in-vivo studies using single-ion beams, while GCR is essentially a mixed radiation field composed of protons (H), helium (He), and heavy ions. Therefore, a sequentially delivered proton (H) → Helium (He) → Oxygen (O) → Silicon (Si) beam was designed to simulate simplified-mixed-field GCR (Smf-GCR), and Apc1638N/+ mice were total-body irradiated to sham or γ (157Cs) or Smf-GCR followed by assessment of GI-tumorigenesis at 150 days post-exposure. Further, GI-tumor data from equivalent doses of heavy-ions (i.e., 0.05 Gy of O and Si) in 0.5 Gy of Smf-GCR were compared to understand the contributions of heavy-ions in GI-tumorigenesis. The Smf-GCR-induced tumor and carcinoma count were significantly greater than γ-rays, and male preponderance for GI-tumorigenesis was consistent with our earlier findings. Comparison of tumor data from Smf-GCR and equivalent doses of heavy ions revealed an association between higher GI-tumorigenesis where dose received from heavy-ions contributed to > 95% of the total GI-tumorigenic effect observed after Smf-GCR. This study provides the first experimental evidence that cancer risk after GCR exposure could largely depend on doses received from constituent heavy-ions.
Keywords: Galactic cosmic radiation; Heavy-ions; Ionizing radiation; Tumorigenesis.
© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.