Directionality of extruded lithium fluoride thermoluminescent dosemeters in a cobalt-60 beam

An experimental investigation of the directionality of commercially available extruded lithium fluoride (LiF:Mg,Ti) thermoluminescent dosemeters was carried out in a cobalt-60 beam at a water depth of 5 cm. One-half of a batch of 60 chips (3.1 x 3.1 x 0.9 mm3) was exposed face-on (faces perpendicular to the beam central axis), and the other half was exposed in an edge-on orientation (two edges perpendicular and faces parallel to the beam axis). Measurements show that an edge-on exposure results in a thermoluminescence reading approximately 0.9% lower than a face-on exposure. Although this is of minor importance in every day patient dosimetry, it is relevant in evaluating errors in in-phantom dosimetric measurements where greater accuracy is required.