title: CT perfusion imaging in response assessment of pulmonary metastases undergoing stereotactic ablative radiotherapy.
abstract: BACKGROUND
  Stereotactic ablative body radiotherapy (SABR) is an emerging treatment technique for pulmonary metastases in which conventional Response Evaluation Criteria in Solid Tumours (RECIST) may be inadequate. This study aims to assess the utility of CT perfusion imaging in response assessment of pulmonary metastases after SABR.
  
  
  METHODS
  In this ethics board-approved prospective study, 11 patients underwent a 26-Gy single fraction of SABR to pulmonary metastases. CT perfusion imaging occurred prior to and at 14 and 70 days post-SABR. Blood flow (mL/100 mL/min), blood volume (mL/100 mL), time to peak (seconds) and surface permeability (mL/100 mL/min), perfusion parameters of pulmonary metastases undergoing SABR, were independently assessed by two radiologists. Inter-observer variability was analysed. CT perfusion results were analysed for early response assessment comparing day 14 with baseline scans and for late response by comparing day 70 with baseline scans. The largest diameter of the pulmonary metastases undergoing SABR was recorded.
  
  
  RESULTS
  Ten patients completed all three scans and one patient had baseline and early response assessment CT perfusion scans only. There was strong level of inter-observer agreement of CT perfusion interpretation with a median intraclass coefficient of 0.87 (range 0.20-0.98). Changes in all four perfusion parameters and tumour sizes were not statistically significant.
  
  
  CONCLUSIONS
  CT perfusion imaging of pulmonary metastases is a highly reproducible imaging technique that may provide additional response assessment information above that of conventional RECIST, and it warrants further study in a larger cohort of patients undergoing SABR.
authors.affiliation: Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia.
authors.forename: Brooke
authors.initials: B
authors.lastname: Sawyer
authors.forename: Emma
authors.initials: E
authors.lastname: Pun
authors.forename: Michael
authors.initials: M
authors.lastname: Samuel
authors.forename: Huilee
authors.initials: H
authors.lastname: Tay
authors.forename: Tomas
authors.initials: T
authors.lastname: Kron
authors.forename: Mathias
authors.initials: M
authors.lastname: Bressel
authors.forename: David
authors.initials: D
authors.lastname: Ball
authors.forename: Shankar
authors.initials: S
authors.lastname: Siva
mesh_terms: D000368:Aged; D000792:Angiography / Q000379:methods*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome
keywords: CT perfusion; RECIST; SABR; pulmonary metastases; stereotactic radiotherapy