[2-component theory and radiation therapy]

The two-component theory which describes the biological effect of X-ray and particle irradiation divides radiation into densely ionizing radiation (ion density in water greater than four ions per 100 A, i.e. LET greater than 12 keV/microns) and loosely ionizing radiation with low ion densities. In case of densely ionizing radiation, the ions can produce breaks of both cords of DNA thus causing the death of the cell (alpha effect). Lower ion densities will produce only slight damages which are possibly lethal but can be partly repaired (beta effect). If the cell parameters are known (L. Cohen 1983), the number of surviving cells after an irradiation can be calculated. The surviving lung cells and tumor cells (squamous cell carcinoma) have been calculated for a pulmonary irradiation with 30 MeV electrons and 200 keV X-rays (single doses of 2 and 5 Gy), respectively. The electron irradiation with single doses of 5 Gy turned out to be the most favorable therapy sparing the greatest number of lung cells and reducing the tumor cells in the most effective way (down to 1.6 x 10(-10)).