Source of Support: None, Conflict of Interest: None
In the western countries cobalt-60 machines have become obsolete, whereas in India we have about 250 machines operational for clinical radiotherapy. The basic differences of '6 MV x-ray beam' and 'cobalt-60 beam' are :- a) build-up dmax point, b) flatness of beam at depths, and c) sharpness of the beam edge. We looked at the homogeneity of delivered dose in the target volume in a 3 field SAD technique for 60Co (80 cm, 100 cm) and 6 MV treatments. More dose variations are seen in 60Co treated volume. The excess curvature of isodose curves of 60Co at depths may be one of the reasons for this in homogeneity in dose to target volume. Therefore, there is need for achieving perfect flatness in the isodose curves at desired depths.