title: Positron emission tomography for predicting pathologic response after neoadjuvant chemoradiotherapy for locally advanced rectal cancer.
abstract: OBJECTIVE
  To investigate whether before and after chemoradiotherapy (CRT) positron emission tomography (PET) predict for pathologic response after preoperative CRT in patients with locally advanced rectal adenocarcinoma.
  
  
  METHODS
  Thirty-five patients who underwent pre-CRT and post-CRT PET scans before surgery were included. All patients were staged with endoscopic ultrasound or high resolution CT. CRT was given with 50.4 Gy at 1.8 Gy per fraction and concurrent 5-fluorouracil-based chemotherapy. Surgery occurred at a median of 46 days (range, 27 to 112 d) after completing CRT. The maximum standardized uptake value (SUV(max)) and the metabolic tumor volume (MTV) using various minimum SUV thresholds (2, 2.5, 3) on the PET scans (MTV(2.0), MTV(2.5), MTV(3.0)) were determined. Post-CRT PET scans were done 3 to 5 weeks after completion of CRT. Pathologic response was assessed using the tumor regression grade (TRG) scale. Patients with complete or near-complete response (TRG=0 to 1) were considered pathologic responders. The pre-CRT and post-CRT PET scan SUV(max) and MTV values were correlated with TRG. The ΔSUV(max) and ΔMTV were correlated with TRG.
  
  
  RESULTS
  No correlation was seen with SUV(max) (P=0.99), MTV(2.0) (P=0.73), MTV(2.5) (P=0.73), or MTV(3.0) (P=0.31) on the pre-CRT PET between pathologic responders versus nonresponders. No correlation was noted between SUV(max) (P=0.49), MTV(2.0) (P=0.73), MTV(2.5) (P=0.49), or MTV(3.0) (P=0.31) on the post-CRT PET scan and pathologic response. Finally, the ΔSUV(max) (P=0.32), ΔMTV(2.0) (P=0.99), ΔMTV(2.5) (P=0.31), ΔMTV(3.0) (P=0.31) did not correlate with pathologic response.
  
  
  CONCLUSIONS
  Changes seen on PET have limited value in predicting for pathologic response of rectal cancer after preoperative neoadjuvant therapy.
authors.affiliation: Department of Radiation Oncology, Stanford University Medical Center, CA, USA.
authors.forename: Sravana K
authors.initials: SK
authors.lastname: Chennupati
authors.forename: Andrew
authors.initials: A
authors.lastname: Quon
authors.forename: Aya
authors.initials: A
authors.lastname: Kamaya
authors.forename: Reetesh K
authors.initials: RK
authors.lastname: Pai
authors.forename: Trang
authors.initials: T
authors.lastname: La
authors.forename: Trevor E
authors.initials: TE
authors.lastname: Krakow
authors.forename: Edward
authors.initials: E
authors.lastname: Graves
authors.forename: Albert C
authors.initials: AC
authors.lastname: Koong
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Chang
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000628:therapy; D059248:Chemoradiotherapy; D019788:Fluorodeoxyglucose F18; D006801:Humans; D020360:Neoadjuvant Therapy; D009367:Neoplasm Staging; D049268:Positron-Emission Tomography; D011300:Preoperative Care; D011379:Prognosis; D019275:Radiopharmaceuticals; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000628:therapy
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18