Tumor cell-killing with radiotherapy

Radiation effects on cells can be better understood and calculated when the more severe, irreparable cell killing caused by high-LET components of radiation (alpha-effects) are distinguished from the less severe, delayed and partly repairable damage (beta-effects) caused by low-LET parts of radiation. Both radiation effects have been treated separately and various influences such as radiation quality, dose dependence and oxygen enhancement are calculated and discussed. The resulting total cell killing values are used to calculate cell survivals for fractionated radiation treatments with various types of radiation. Aerobic and hypoxic cells are treated separately. Reoxygenation of hypoxic cells is described by a "conversion factor K" indicating the relative part of the hypoxic cells being reoxygenated and converted after each irradiation. The calculations show that also for high-LET radiations, such as pion and neutron therapy, the reoxygentation process is of importance. Calculated RBE and Co-RBE factors are given.