Measurement of relative output for 90Sr ophthalmic applicators using radiochromic film

The treatment of various superficial lesions of the eye has, for many years, been conducted using strontium 90 (90Sr) ophthalmic applicators that have a steep dose gradient near their surface. A new applicator acquired by a treatment facility must have its output compared with that of any older applicators already in use to ensure consistent treatments. These measurements may be done using available dosimeters such as film and thermoluminescent detectors. Our work made use of radiochromic film and a document scanner to perform relative output measurements for 4 different 90Sr ophthalmic applicators acquired from the same manufacturer (Amersham Healthcare, Arlington Heights, IL) over a span of 28 years. Relative outputs were found to vary by < 10% with respect to the manufacturer's values, which is well within the uncertainty limit for absolute output of 20% specified by the manufacturer. The film measurements were verified using thermoluminescent dosimeters. Radiochromic film was also used to obtain a percentage depth dose curve and a 2 dimensional isodose distribution in a plane perpendicular to the active surface for the newest applicator (SIA 20).