Dose computation for irregular fields in cobalt-60 beam

Dose computation in large irregular fields used for treating certain malignant tumors cannot be done by equivalent field methods. The present methods available for such dose computations are accurate but complicated and tedious and are amenable to only computers. This paper describes an algorithm (a semiempirical formula) of dose computation in an irregular field. Attempt is also made to estimate the dose outside the field border and in the shielded region. The dose values computed with this method at different depths in mantle and inverted Y-field in a cobalt-60 beam are compared with the experimentally measured values. The method proves to be simple and accurate. The calculations can be done even manually with a calculator and a statistical table in the absence of computer facility. It also successfully estimates the dose in the shielded region and in the penumbra.