title: The importance of scatter correction for the assessment of lung shunting prior to yttrium-90 radioembolization therapy.
abstract: BACKGROUND
  Treatment of inoperable hepatocellular carcinoma or secondary metastases by radioembolization using yttrium-90 (90Y) microspheres is a promising method for the treatment of unresectable liver metastases. A pretreatment scintigraphy planar scan using 99mTc-labelled macroaggregated albumin (99mTc-MAA) injected directly into the hepatic artery is carried out to assess the degree of portal shunting of blood between the liver and the lungs. The quantitative results of this scan are used to modulate the activity of therapeutic 90Y microspheres injected into the patient to limit the radiation dose received by the lungs. The presence of scattered events in the MAA lung shunt scan leads to an overestimation of the true shunting ratio, which in turn leads to the administered therapeutic activity being lowered unnecessarily to comply with the protocols of radiation protection. Overall, this may impact the efficacy of treatment.
  
  
  METHODS
  This study analyses the impact of a window-based analytical scatter-correction method on lung shunt analysis using an anthropomorphic torso phantom, and retrospectively analysed three patient case studies.
  
  
  RESULTS
  Our results of scatter in the phantom show a marked decrease in the lung shunt percentage. Clinical analysis of patient data shows that the lung shunt percentage can be overestimated by up to 50% in clinical cases, and depending on the lung shunt percentage, the efficacy of treatment by therapeutic dose reduction may be compromised.
  
  
  CONCLUSIONS
  Our results indicate that scatter correction should be used on 90Y pretreatment 99mTc-MAA scans in order to more accurately assess the lung shunting percentage before therapy.
authors.affiliation: Department of Nuclear Medicine, St Lukes Wing, Royal Surrey County Hospital, Guildford, UK. jim.o'doherty@nhs.net
authors.forename: Jim
authors.initials: J
authors.lastname: O'Doherty
authors.forename: James
authors.initials: J
authors.lastname: Scuffham
authors.forename: Paul
authors.initials: P
authors.lastname: Hinton
mesh_terms: D016477:Artifacts; D004621:Embolization, Therapeutic; D006801:Humans; D008168:Lung / Q000502:physiology*; D008863:Microspheres; D019047:Phantoms, Imaging; D012039:Regional Blood Flow; D012542:Scattering, Radiation; D014692:Ventilation-Perfusion Ratio; D015021:Yttrium Radioisotopes / Q000737:chemistry / Q000627:therapeutic use
chemical_list: D015021:Yttrium Radioisotopes