Assessment of the relative contribution of volume and concentration changes in Yttrium-90 labelled resin microspheres on ionization chamber measurements

Re-entrant ionization chambers or, “dose calibrators”, are the standard equipment used to assay radiopharmaceuticals in clinical practice. These devices consist of a gas-filled (usually argon), pressurized ionization chamber surrounding a well in which the source is placed. When calibrated they can provide a measurement of radioactivity with a linear response over a very wide range of values [ 1 ]. The readout of the device is the current recorded from the chamber multiplied by a calibration factor [ 2 ]. This calibration factor is specific for the isotope being assayed and the geometry of the source. Generally radioactivity in a glass ampoule or vial is used to measure the accuracy of the dose calibrator against a national standard. In the clinical setting the radioactivity can be measured using a variety of vessels and source volumes such as syringes and glass or plastic vials.