The calculation and measurement of exposure distributions from 60 Co ophthalmic applicators.

Abstract The paper discusses the calculation and measurement of exposure distributions from 60Co γ-ray ophthalmic applicators used in the treatment of retinoblastoma in children. Exposures within the eye were calculated assuming an inverse square law attenuation with no absorption. Photographic emulsions were used to measure the exposure distributions, and corrections for depth and angular dependence of film sensitivity and reciprocity failure were estimated. It was found that agreement between calculation and measurement was reasonable except near the applicator surface, where the measured values were thought to be more correct. New values of “design depth”, the maximum depth of tumour each applicator is intended to treat, are presented.