title: Characterization of geometric uncertainties of a dose calibrator during measurement of 90Y activity.
abstract: The performance and measurement of (90)Y with a dose calibrator has always been a key point of several international recommendations, specifically in the case of the radiopharmaceutical (90)Y-ibritumomab tiuxetan, among other applications, used in the treatment of non-Hodgkin lymphoma. The objective of the present work was to examine in detail some important sources of geometric errors that, if neglected, can lead to an increase in uncertainty about the measured activity of this β(-) emitter radionuclide.
  
  
  METHODS
  A CRC-15R dose calibrator was used to measure and quantify some of these sources, although the same methodology can easily be applied to any other similar equipment. The depth response along the main axis of the dose calibrator was carefully characterized, as well as syringe volume effects and source angular dependence.
  
  
  RESULTS
  It was found that, if not taken properly into account, these issues can contribute to an increase in the activity uncertainty (e.g., 5.1% in the present example). This finding implies the possibility of easily reaching higher values than the internationally suggested 5% uncertainty in activity measurement for therapeutic purposes.
  
  
  CONCLUSIONS
  These errors can be greatly reduced by previous characterization of the dose calibrator and careful implementation of the methodology for measurement.
authors.affiliation: Serviço de Física Médica and Centro de Investigação, Instituto Português de Oncologia do Porto Francisco Gentil, E.P.E, Porto, Portugal. j.a.miranda.santos@gmail.com
authors.forename: João A M
authors.initials: JA
authors.lastname: Santos
authors.forename: Anabela G
authors.initials: AG
authors.lastname: Dias
authors.forename: Artur L
authors.initials: AL
authors.lastname: Bastos
mesh_terms: D002138:Calibration; D011874:Radiometry / Q000295:instrumentation*; D013594:Syringes; D035501:Uncertainty; D015021:Yttrium Radioisotopes
chemical_list: D015021:Yttrium Radioisotopes