Dosimetry of normally and obliquely incident cobalt-60 teletherapy beams

Standard isodose charts are generally given by the manufacturer for normal incidence of radiation beams of various qualities. These charts are used for routine treatment planning in a radiotherapy department. Due to the enormous variety of the cases encountered in the department, the physicist often runs short of appropriate charts required for specific treatment planning. Besides, the plan sometimes needs a beam directed at an angle to the patient's surface. As a result, isodose charts for individual treatment plans are desirable for precise delivery of the requisite dose to the tumour volume. In this paper a computer method is described for determining dose distributions for normally and obliquely incident 60Co beam. The experimental verification of the computed results using a 0.4 cm3 ionization chamber and a perspex water phantom assembly is also presented. The results are found to be in good agreement.