Source:http://linkedlifedata.com/resource/umls/id/C2955689
UMD: Plates designed to become fluorescent temporarily when activated by ionizing radiation (i.e., photons and electrons). These devices consist of a plate with a substrate typically made of acrylic or polycarbonate and a fluorescent material; the plate displays permanent graduated (e.g., in centimeters or inches) marks showing the active radiation field areas a short time after the radiation is turned off. The use of appropriate filters avoids activation of the phosphor by other light sources. Ionizing radiation alignment plates are intended to align the radiation field in relation to the treatment table during periodic quality assurance measurements according to established standards and/or recommendations.