Simulation of neutron interactions at the single-cell level.
We recently reported that the exposure of cancer cells to 14 MeV neutrons at a very low dose rate (0.8 mGy min(-1)) produced a marked increase in cell killing at 5 cGy, followed by a plateau in survival and chromosomal damage. Simulation of the energy deposition events in irradiated cells may help to explain these unusual cell responses. We describe here a Monte Carlo simulation code, Energy Deposition in Cells Irradiated by Neutrons (EDCIN). The procedure considered the experimental setup and a hemispheric cell model. The simulation data fitted the dosimetric measurements performed using tissue-equivalent ionization chambers, Geiger-Müller counters, fission chambers, and silicon diodes. The simulation showed that 80% of the energy deposited in a single cell came from the interactions of neutrons outside the cell and only 20% came from neutron interactions inside the cell. Thus the "external" interactions that result in the production of recoil protons and secondary electrons may induce most of the biological damage, which may be repaired efficiently at low dose rate. The repair process may be triggered from a threshold level of damage, which would explain an initial increase cell death due to unrepaired sublethal damage, and then may compensate for induced damage, resulting in the plateaus.
Alard
Jean-Pierre
JP
Laboratoire de Physique Corpusculaire, Université Blaise Pascal, IN2P3/CNRS, 63177 Aubière, France.
Bodez
Véronique
V
Tchirkov
Andrei
A
Nénot
Marie-Laure
ML
Arnold
Jack
J
Crespin
Sylvain
S
Rapp
Maryse
M
Verrelle
Pierre
P
Dionet
Claude
C
D016923:Cell Death / Q000528:radiation effects; D002467:Cell Nucleus / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008545:Melanoma / Q000473:pathology; D008954:Models, Biological; D009502:Neutrons / Q000009:adverse effects*; D011522:Protons; D011829:Radiation Dosage; D013997:Time Factors; D014407:Tumor Cells, Cultured
D011522:Protons