Oncogenic transformation in C3H10T1/2 cells by low-energy neutrons.
OBJECTIVE
Occupational exposure to neutrons typically includes significant doses of low-energy neutrons, with energies below 100 keV. In addition, the normal-tissue dose from boron neutron capture therapy will largely be from low-energy neutrons. Microdosimetric theory predicts decreasing biological effectiveness for neutrons with energies below about 350 keV compared with that for higher-energy neutrons; based on such considerations, and limited biological data, the current radiation weighting factor (quality factor) for neutrons with energies from 10 keV to 100 keV is less than that for higher-energy neutrons. By contrast, some reports have suggested that the biological effectiveness of low-energy neutrons is similar to that of fast neutrons. The purpose of the current work is to assess the relative biological effectiveness of low-energy neutrons for an endpoint of relevance to carcinogenesis: in vitro oncogenic transformation.


METHODS
Oncogenic transformation induction frequencies were determined for C3H10T1/2 cells exposed to two low-energy neutron beams, respectively, with dose-averaged energies of 40 and 70 keV, and the results were compared with those for higher-energy neutrons and X-rays.


RESULTS
These results for oncogenic transformation provide evidence for a significant decrease in biological effectiveness for 40 keV neutrons compared with 350 keV neutrons. The 70 keV neutrons were intermediate in effectiveness between the 70 and 350 keV beams.


CONCLUSIONS
A decrease in biological effectiveness for low-energy neutrons is in agreement with most (but not all) earlier biological studies, as well as microdosimetric considerations. The results for oncogenic transformation were consistent with the currently recommended decreased values for low-energy neutron radiation weighting factors compared with fast neutrons.
Miller
R C
RC
Center for Radiological Research, Columbia University, New York, NY 10032, USA.
Marino
S A
SA
Napoli
J
J
Shah
H
H
Hall
E J
EJ
Geard
C R
CR
Brenner
D J
DJ
D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000528:radiation effects*; D016018:Least-Squares Analysis; D016013:Likelihood Functions; D051379:Mice; D009502:Neutrons / Q000009:adverse effects*; D012062:Relative Biological Effectiveness