[Patterns of the formation of a dosage field in arranging 252Cf and 60Co sources in a single plane]

A computerized study was made of a change in the correlation between the sizes of an irradiated volume and the distribution of sources. Criteria have been established for the utilization of 252Cf and 60Co sources of different active length and design placed on the same plane. Reference dose rate and its derivatives have been chosen as the main parameters that characterize a dose field. A dosimetric analysis was performed using the data for an absorbed dose of neutrons in the tissue, taking account of high RBE of 252Cf fast neutrons that equals 6-7, and a slight change of the local RBE value near the source resulting from a change of the effective spectrum of neutrons in combination with the growth of a contribution of gamma-radiation into the summary dose with the removal from the source. The irradiated volume was evaluated by introducing 3 linear parameters--length, thickness and width. It has been shown that the ratio of the length of an irradiated volume to the active length of 252Cf sources with radionuclide regular linear density changes from 0.7 with the isodose value of 85% up to 0.97 with the isodose value of 60%. For 60Co sources with a higher linear density of the radionuclide on the edges the lower limit of this value equals 1. Intervals of changes in the rest of parameters have also been defined. The results obtained are presented graphically. The results of the study are used for a dosimetric control of the clinical trials of 252Cf and 60Co sources in the treatment of patients with tumors of the tongue, oral cavity fundus, lip and other sites.