title: The value of liver-based standardized uptake value and other quantitative 18F-FDG PET-CT parameters in neoadjuvant therapy response in patients with locally advanced rectal cancer: correlation with histopathology.
abstract: OBJECTIVE
  We aimed to investigate the value of PET-CT in therapy response and the correlation of quantitative PET parameters with histopathologic results in patients with locally advanced rectal cancer (LARC) before and after neoadjuvant chemoradiotherapy. We also analyzed the correlation of PET-CT parameters between Ki-67 and glucose transporter 1 (GLUT1).
  
  
  METHODS
  A total of 29 patients diagnosed with LARC who had undergone a biopsy between 2009 and 2012 were included in our study. Quantitative PET parameters [standardized uptake value (SUV)max-mean, lean body mass SUV(max-mean), tumor/liver SUV, retention index , and [INCREMENT]SUV(max)] were measured before and after therapy using PET-CT. Tumor regression grade (TRG) was evaluated according to Wheeler's classification. Patients in grade 1 were considered responders, whereas patients at grades 2 and 3 were considered nonresponders. Immunohistochemical staining with Ki-67 and GLUT1 was performed on biopsy and surgical specimens. The correlation between staining ratios and SUV was also investigated.
  
  
  RESULTS
  SUV parameters were significantly decreased after therapy (P < 0.001). Twelve (41%) patients were at TRG1, 10 (35%) were at TRG2, and seven (24%) were at TRG3. A cutoff SUV(max) of 5.05 to discriminate between responders and nonresponders after treatment revealed a sensitivity of 57%, specificity of 73%, negative predictive value of 65%, positive predictive value of 67%, and accuracy of 66%. Using a cutoff of 3.55 for the SUV(mean) (standardized measurement of SUV with 1.2-cm-diameter region of interest) revealed a sensitivity, specificity, negative predictive value, positive predictive value, and accuracy of 67, 76, 67, 76, and 72%, respectively. For a cutoff of 1.95 for the tumor SUV(mean)/liver SUV(mean), these diagnostic values after therapy were 73, 78, 82, 67, and 76%, respectively. We found a moderate correlation between liver-based SUV(max) (r = -0.35, P = 0.019) and SUV(mean )(r = -0.31, P = 0.036) with GLUT1 after therapy. Quantitative PET parameters and retention index were moderately correlated with Ki-67.
  
  
  CONCLUSIONS
  PET-CT is a useful method for assessing the response to neoadjuvant chemoradiotherapy in patients with LARC. The most significant parameter for assessing treatment response using SUV parameters is the tumor/liver ratio.
authors.affiliation: aDepartment of Nuclear Medicine, Atatürk Government Hospital, Aydin bDepartment of Nuclear Medicine, School of Medicine, Yüzüncü Yil University, Van Departments of cNuclear Medicine dPathology eRadiology fMedical Oncology gRadiation Oncology hGeneral Surgery, School of Medicine, Dokuz Eylül University, Izmir, Turkey.
authors.forename: Murat
authors.initials: M
authors.lastname: Koç
authors.forename: Gamze Ç
authors.initials: GÇ
authors.lastname: Kaya
authors.forename: Yusuf
authors.initials: Y
authors.lastname: Demir
authors.forename: Erdem
authors.initials: E
authors.lastname: Sürücü
authors.forename: Sülen
authors.initials: S
authors.lastname: Sarioğlu
authors.forename: Funda
authors.initials: F
authors.lastname: Obuz
authors.forename: İlhan
authors.initials: İ
authors.lastname: Öztop
authors.forename: İlknur B
authors.initials: İB
authors.lastname: Görken
authors.forename: Selman
authors.initials: S
authors.lastname: Sökmen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001692:Biological Transport; D059248:Chemoradiotherapy; D005260:Female; D019788:Fluorodeoxyglucose F18; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D006801:Humans; D019394:Ki-67 Antigen / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D020360:Neoadjuvant Therapy; D049268:Positron-Emission Tomography; D012004:Rectal Neoplasms / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
chemical_list: D051272:Glucose Transporter Type 1; D019394:Ki-67 Antigen; D019788:Fluorodeoxyglucose F18