title: Optimal timing for assessment of tumor response to neoadjuvant chemoradiation in patients with rectal cancer: do all patients benefit from waiting longer than 6 weeks?
abstract: OBJECTIVE
  To estimate the metabolic activity of rectal cancers at 6 and 12 weeks after completion of chemoradiation therapy (CRT) by 2-[fluorine-18] fluoro-2-deoxy-d-glucose-labeled positron emission tomography/computed tomography ([(18)FDG]PET/CT) imaging and correlate with response to CRT.
  
  
  METHODS
  Patients with cT2-4N0-2M0 distal rectal adenocarcinoma treated with long-course neoadjuvant CRT (54 Gy, 5-fluouracil-based) were prospectively studied (ClinicalTrials.org identifier NCT00254683). All patients underwent 3 PET/CT studies (at baseline and 6 and 12 weeks from CRT completion). Clinical assessment was at 12 weeks. Maximal standard uptake value (SUVmax) of the primary tumor was measured and recorded at each PET/CT study after 1 h (early) and 3 h (late) from (18)FDG injection. Patients with an increase in early SUVmax between 6 and 12 weeks were considered "bad" responders and the others as "good" responders.
  
  
  RESULTS
  Ninety-one patients were included; 46 patients (51%) were "bad" responders, whereas 45 (49%) patients were "good" responders. "Bad" responders were less likely to develop complete clinical response (6.5% vs. 37.8%, respectively; P=.001), less likely to develop significant histological tumor regression (complete or near-complete pathological response; 16% vs. 45%, respectively; P=.008) and exhibited greater final tumor dimension (4.3 cm vs. 3.3 cm; P=.03). Decrease between early (1 h) and late (3 h) SUVmax at 6-week PET/CT was a significant predictor of "good" response (accuracy of 67%).
  
  
  CONCLUSIONS
  Patients who developed an increase in SUVmax after 6 weeks were less likely to develop significant tumor downstaging. Early-late SUVmax variation at 6-week PET/CT may help identify these patients and allow tailored selection of CRT-surgery intervals for individual patients.
authors.affiliation: Department of Gastroenterology, Colorectal Surgery Division, University of São Paulo School of Medicine, São Paulo, Brazil.
authors.forename: Rodrigo O
authors.initials: RO
authors.lastname: Perez
authors.forename: Angelita
authors.initials: A
authors.lastname: Habr-Gama
authors.forename: Guilherme P
authors.initials: GP
authors.lastname: São Julião
authors.forename: Joaquim
authors.initials: J
authors.lastname: Gama-Rodrigues
authors.forename: Afonso H S
authors.initials: AH
authors.lastname: Sousa
authors.forename: Fabio Guilherme
authors.initials: FG
authors.lastname: Campos
authors.forename: Antonio R
authors.initials: AR
authors.lastname: Imperiale
authors.forename: Patricio B
authors.initials: PB
authors.lastname: Lynn
authors.forename: Igor
authors.initials: I
authors.lastname: Proscurshim
authors.forename: Sergio Carlos
authors.initials: SC
authors.lastname: Nahas
authors.forename: Carla Rachel
authors.initials: CR
authors.lastname: Ono
authors.forename: Carlos Alberto
authors.initials: CA
authors.lastname: Buchpiguel
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000401:mortality / Q000473:pathology / Q000628:therapy*; D000328:Adult; D000465:Algorithms; D059186:Chemoradiotherapy, Adjuvant / Q000379:methods*; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods; D020360:Neoadjuvant Therapy / Q000379:methods*; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000401:mortality / Q000473:pathology / Q000628:therapy*; D012044:Regression Analysis; D012074:Remission Induction / Q000379:methods; D016019:Survival Analysis; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18