Dosimetry of Sr‐90 ophthalmic applicators

Abstract

Sr-90 ophthalmic applicators are commonly used for the treatment of superficial eye disorders. Although a variety of dosimetric devices such as film, thermoluminescent dosimeters (TLD's), ion chambers, and radiochromic foils have been used to measure the peak dose at the applicator surface, there is no internationally agreed upon calibration procedure. Recently, large discrepancies among calibrations of the same applicator at three institutions have been reported. Here we describe a technique to obtain the peak dose rate at the applicator surface using LiF TLD's. The technique can be used for the calibration of flat as well as curved surface applicators. Results for two flat and three concave applicators are presented. Our measurement of the surface dose rate for one of the flat applicators is compared with those obtained by four other institutions, each using different dosimetric devices.

Breast cancer following radiotherapy for a hemangioma during childhood

“…This leads to large errors in dose estimations, which is the reason for the limited availability of estimations with such particles. The few experimental data available and all the theoretical published data show that the absorbed doses from beta sources are attenuated to negligible values in the first 1 cm from the source [26][27][28][29][30]. Misspecification of about 1 cm may induce large differences between the true dose and the estimated dose.…”

NCS Report 14: Quality control of sealed beta sources in brachytherapy

“…The use of parallel plate ionization chambers has been described for measurements on planar strontium sources [34,39,40]. Because of the large electrode size (at least 5 mm), these chambers are not suitable for characterization of the activity distribution of a source.…”

“…Although most hospitals make use of TLDs for dosimetry, dedicated TLDs are required for measurements on beta sources [34,40,41,56]. The most important property of these TLDs is their small size (as small as 0.1 mm thickness and 1 mm diameter for the active volume), which makes them suitable for determining the spatial distribution of the dose around a source.…”

Calculating lens dose and surface dose rates from ophthalmic applicators using Monte Carlo modeling

“…Other methods used to determine surface dose rate include diodes, thermoluminescent dosimeters ͑TLDs͒, and radiochromic foils. 20 Although surface dose rate has no true physical meaning since dose is defined on a per unit mass basis, there is a mathematical method which uses the extrapolation of measured values to find this theoretical value. The advantage of using surface dose rate is that it provides a simple means of estimating the dose being delivered to the sclera for each treatment.…”