title: Radiobiological Modeling Based on18F-Fluorodeoxyglucose Positron Emission Tomography Data for Esophageal Cancer.
abstract: BACKGROUND
  We investigated the relationship of standardized uptake values (SUVs) to radiobiological parameters, such a 25 s tumor control probability (TCP), to allow for quantitative prediction of tumor response based on SUVs from18F fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) before and after treatment for esophageal cancer.
  
  
  METHODS
  We analyzed data from 20 esophageal cancer patients treated with chemoradiotherapy (CRT) followed by surgery. Tumor pathologic response to CRT was assessed in surgical specimens. Patients underwent18F-FDG PET imaging before and after CRT. Rigid image registration was performed between both images. Because TCP in a heterogeneous tumor is a function of average cell survival, we modeled TCP as a function of <SUVR>, a possible surrogate for average cell survival (<SUVR>=<SUVafter/SUVbefore>). TCP was represented by a sigmoid function with two parameters: SUVR50, the <SUVR> at which TCP=0.5, and γ50, the slope of the curve at SUVR50. The two parameters and their confidence intervals (CIs) were estimated using the maximum-likelihood method. The correlation between SUV before CRT and SUV change <SUVbefore- SUVafter> was also studied.
  
  
  RESULTS
  A TCP model as a function of SUV before and after treatment was developed for esophageal cancer patients. The maximum-likelihood estimate of SUVR50was 0.47 (90% CI, 0.30-0.61) and for γ50was 1.62 (90% CI, 0-4.2). High initial SUV and larger metabolic response (larger <SUVbefore-SUVafter>) were correlated, and this correlation was stronger among responders.
  
  
  CONCLUSIONS
  Our TCP model indicates that <SUVafter/SUVbefore> is a possible surrogate for cell survival in esophageal cancer patients. Although CIs are large as a result of the small patient sample, parameters for a TCP curve can be derived and an individualized TCP can be calculated for future patients. Initial SUV does not predict response, whereas a correlation is found between surrogates for initial tumor burden and cell kill during therapy.
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, 21201, USA.
authors.forename: Mariana
authors.initials: M
authors.lastname: Guerrero
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, 21201, USA ; Department of Intelligent Science and Technology, School of Automation, Huazhong University of Science and Technology, Wuhan, China.
authors.forename: Shan
authors.initials: S
authors.lastname: Tan
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, 21201, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Lu
keywords: 18F-FDG PET/CT; Esophageal cancer; Quantitative imaging; Radiation therapy; Tumor response