Thursday, February 18, 2016

Effects of Radiation on Cancer in Mice - Lung Cancer Mortality

There are three studies that address the effects of ionizing radiation on lung cancer mortality in mice. The most recent of these was a 1997 experiment by Y. Hosoi and K. Sakamoto [Suppression of spontaneous and artificial tumors by low dose total body irradiation in mice. In Low Doses of Ionizing Radiation: Biological Effects and Regulatory Control, Atomic Energy Agency, TECDOC-976, Vienna, 1997] in which mice were injected with artificial metastases (a fancy medical term for cancer cells) and then irradiated with gamma rays up to 100 cGy (100,000 mrad). Data showed the lowest cancer rate in a range between 15 and 40 cGy, with the minimum being 41% of controls at 15 cGy.

The Hosoi-Sakamoto study demonstrated another tenet of the hormesis theory, however, which most other experimenters have neglected to investigate - namely that hormesis is a property of the organism and not its individual cells. When tumor cells that had been irradiated with 10 to 50 cGy gamma rays in vitro were injected in the mice, there was no difference from the controls - indicating that the suppression affects the mouse, not tumor cells. Unfortunately, the study involved only 200 - 250 mice (perhaps they are scarce in Japan?) and lacks the statistical significance I would like to see for compelling evidence.

Both of the lung cancer experiments were performed by Ullich et al., whom we have seen laboring earlier with mouse pituitaries; and both experiments involved several thousand mice. His 1977 investigation [Ullrich, R.L., et al. Neutron carcinogenesis. Dose and dose-rate effects in BALB.C mice. Radiation Research, 72, 487, 1977], which showed a minimum lung cancer mortality in the area of 100 cSv, was repeated in 1979 [Ullrich, R.L., et al. Influence of irradiation on the development of neoplastic disease in mice. Radiation Research, 80, 135, 1979]. This time, instead of only two data points, six were examined from 10 to 300 cSv. As shown in Figure 9, the minimum appeared around 25 cSv in the 1979 data but was still significantly lower than controls even at the 100 cSv level.

At the risk of sounding repetitive, it is evident that the LNT is completely inadequate to explain this phenomenon, while the hormesis theory predicts just such an occurrence.

Caption for Figure 9 Lung Cancer Mortality in Mice Source: Ullrich, R.L., Jernigan, M.C., and Storer, J.B. Neutron carcinogenesis. Dose and dose-rate effects in BALB/C Mice, Radiation Research, 72, 487, 1977. Also Ullrich, R.L., and Storer, J.B. Influence of irradiation on the development of neoplastic disease in mice. I. Reticular tissue tumors. II. Solid tumor. III. Dose-rate effects. Radiation Research, 80, 135, 1979.