title: Differentiation of tumor recurrence from radiation-induced pulmonary fibrosis after stereotactic ablative radiotherapy for lung cancer: characterization of 18F-FDG PET/CT findings.
abstract: OBJECTIVE
  Stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiotherapy (SBRT), is now a standard treatment option for patients with stage I non-small cell lung cancer or oligometastatic lung tumor who are medically inoperable or medically operable but refuse surgery. When mass-like consolidation is observed on follow-up CT after SABR, it is sometimes difficult to differentiate tumor recurrence from SABR-induced pulmonary fibrosis. In this study, we evaluated the role of (18)F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) in differentiating tumor recurrence from radiation fibrosis after SABR.
  
  
  METHODS
  Between June 2006 and June 2009, 130 patients received SABR for stage I non-small cell lung cancer or metastatic lung cancer at our institution. Fifty-nine patients of them were imaged with FDG-PET/CT after SABR. There were a total of 137 FDG-PET/CT scans for retrospective analysis. The FDG uptake in the pulmonary region was assessed qualitatively using a 3-point scale (0, none or faint; 1, mild; or 2, moderate to intense), and the shape (mass-like or non mass-like) was evaluated. For semi-quantitative analysis, the maximum standardized uptake value (SUV(max)) was calculated.
  
  
  RESULTS
  Sixteen of 59 patients had local failure. In recurrent tumor, the combination of intensity grade 2 and mass-like shape was most common (21/23; 91%). By contrast, in cases of radiation fibrosis, the combination of intensity grade 0 or 1 and non mass-like shape was most common (48/59; 81%). The SUV(max) of tumor recurrence after 12 months was significantly higher than that of radiation fibrosis (8.0 ± 3.2 vs. 2.1 ± 0.9, p < 0.001), and all tumor recurrence showed the SUV(max) > 4.5 at diagnosis of local failure. At ≥12 months after SABR, these two variables, the combination of intensity 2 and mass-like FDG uptake or SUV(max) > 4.5 acquired a significant high predictive value of local recurrence, finding sensitivity 100% and specificity 100% for both of them.
  
  
  CONCLUSIONS
  The combination of FDG uptake patterns and SUV(max) was useful for distinguishing tumor recurrence from radiation fibrosis after SABR.
authors.affiliation: Department of Radiation Oncology, National Hospital Organization Shikoku Cancer Center, Kou-160, Minamiumemoto-machi, Matsuyama, Ehime 791-0280, Japan. haruhi0321@gmail.com
authors.forename: Naomi
authors.initials: N
authors.lastname: Nakajima
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Sugawara
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kataoka
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Hamamoto
authors.forename: Takashi
authors.initials: T
authors.lastname: Ochi
authors.forename: Shinya
authors.initials: S
authors.lastname: Sakai
authors.forename: Tadaaki
authors.initials: T
authors.lastname: Takahashi
authors.forename: Makoto
authors.initials: M
authors.lastname: Kajihara
authors.forename: Norihiro
authors.initials: N
authors.lastname: Teramoto
authors.forename: Motohiro
authors.initials: M
authors.lastname: Yamashita
authors.forename: Teruhito
authors.initials: T
authors.lastname: Mochizuki
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001692:Biological Transport; D003937:Diagnosis, Differential; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D011658:Pulmonary Fibrosis / Q000000981:diagnostic imaging* / Q000378:metabolism; D011832:Radiation Injuries / Q000000981:diagnostic imaging* / Q000378:metabolism; D016634:Radiosurgery / Q000009:adverse effects*; D012008:Recurrence; D014057:Tomography, X-Ray Computed
chemical_list: D019788:Fluorodeoxyglucose F18