Dosimetry requirements for reproduction accuracy of certain parameters of remote gamma units for radiotherapy

The combined effect is considered of parameters of the gamma-therapeutic unit (errors in the regulation of field dimensions, angle of the displacement, speed of the rotation of the radiation head, the screening time of the source by shutter) on the characteristics of the dose field. The maximum deviation of the relative dose from the nominal one at the margin of the 80 per cent dose contour has been used as a criterium of the evaluation. The determination and the calculation are given of the dose in the supporting point-the main characteristics of the dose field - and errors during its determination. It is shown that the main error occurs during the determination of the contour and structure of the irradiated section. It is also shown that errors of the reproduction of parameters of the dose deviation from the nominal one at the margin of the 80 per cent contour and the dose in the supporting point can average 10 per cent, when the error of the gauge is (<=)5 per cent