An optical method of estimating the relative output of a superficial unit for small applicators.

The uncertainties associated with the measurement of the radiation output from a superficial x-ray unit are increased when using small applicators, as discussed in the text. The method described here uses two stages to measure the relative outputs: the first stage uses a large-diameter flat chamber to measure the radiation integrated over the applicator end, and the second stage uses an optical imaging system to investigate the shape of the beam. These are combined to produce a relative output for each applicator, which may then be transformed to an absolute output by applying the relative factors to a direct measurement of absolute output on one of the larger applicators.