title: Temporal evolution of administered activity in cardiac gated SPECT and patients' effective dose: analysis of an historical series.
abstract: OBJECTIVE
  Myocardial perfusion imaging contributes >20 % of the average medical radiation exposure to the population in the USA. Imaging protocols able to achieve a radiation exposure ≤9 mSv in 50 % of the studies by 2014 have been recommended. The aim of this study was to analyse the temporal evolution of administered activities in patients scheduled for dual-day (99m)Tc tracer gated single photon emission computed tomography (SPECT) and to compare different dose administration protocols in terms of patients' effective dose.
  
  
  METHODS
  Patients evaluated from 1 July 2002 to 31 January 2012 were allocated according to the protocol adopted: group 1: fixed activity according to diagnostic reference level: 740 MBq up to 80 kg (adapted for weight <60 kg); 900 MBq 80-100 kg, 1,110 MBq >100 kg, standard filtered back-projection (FBP) reconstruction; group 2: weight-adjusted activity: 8 MBq/kg up to 1,110 MBq, standard FBP reconstruction; and group 3: 4 MBq/kg, UltraSPECT wide beam reconstruction (WBR) reconstruction. A dual-head Anger camera (GE Helix) was used.
  
  
  RESULTS
  A total of 9,060 patients were allocated to different groups: 4,751 in group 1, 2,844 in group 2 and 1,465 in group 3. The stress + rest administered activity was 1,617 ± 180 in group 1, 1,136 ± 260 in group 2 and 682 ± 164 MBq in group 3 (all p < 0.001). Patients' effective dose was 13.7 ± 3 in group 1, 9.5 ± 2.8 in group 2 and 5.7 ± 1.6 mSv in group 3 (all p < 0.001). The 50th percentile was 12.6 in group 1, 9.1 in group 2 and 5.3 mSv in group 3. The effective dose received by the dedicated cardiologists was 2.1, 1.5 and 1.0 μSv/exam in group 1, group 2 and group 3 periods, respectively (all p < 0.001).
  
  
  CONCLUSIONS
  A significant reduction over time in the administered activity for gated SPECT was achieved; accordingly, a significant reduction in patients' exposure was obtained. A simple weight-adjusted strategy with 8 MBq/kg immediately fulfils the recommendations to limit exposure. In selected group 3 patients, a stress-only strategy allows for studies with <3 mSv exposure. Thus, at least the adoption of a new reconstruction algorithm is strongly encouraged, and suggested tracer activities for cardiac gated SPECT are to be revised.
authors.affiliation: Cardiology Dept., S. Maugeri Fnd, IRCCS, Scientific Institute of Veruno, V. Per Revislate 13, 28010, Veruno, Italy. claudio.marcassa@fsm.it
authors.forename: C
authors.initials: C
authors.lastname: Marcassa
authors.forename: O
authors.initials: O
authors.lastname: Zoccarato
authors.forename: P
authors.initials: P
authors.lastname: Calza
authors.forename: R
authors.initials: R
authors.lastname: Campini
mesh_terms: D000368:Aged; D055426:Cardiac-Gated Single-Photon Emission Computer-Assisted Tomography / Q000009:adverse effects / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D055414:Myocardial Perfusion Imaging / Q000009:adverse effects; D016273:Occupational Exposure / Q000032:analysis; D011829:Radiation Dosage; D012189:Retrospective Studies; D017256:Technetium Tc 99m Sestamibi / Q000009:adverse effects; D013997:Time Factors
chemical_list: D017256:Technetium Tc 99m Sestamibi