Abstract
BackgroundWe 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 from 18F fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) before and after treatment for esophageal cancer.MethodsWe 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 underwent 18F-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.ResultsA TCP model as a function of SUV before and after treatment was developed for esophageal cancer patients. The maximum-likelihood estimate of SUVR50 was 0.47 (90% CI, 0.30-0.61) and for γ50 was 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.ConclusionsOur 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.
Highlights
18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) is routinely used as a tool to diagnose and evaluate response in many cancer sites
confidence intervals (CIs) are large as a result of the small patient sample, parameters for a tumor control probability (TCP) curve can be derived and an individualized TCP can be calculated for future patients
The purpose of this work is to investigate the quantitative relationship between mean patient standardized uptake value (SUV) and radiobiological parameters to facilitate quantitative prediction of tumor response based on SUVs from 18F fluorodeoxyglucose (18F-FDG) PET before and after treatment
Summary
18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) is routinely used as a tool to diagnose and evaluate response in many cancer sites. The purpose of this work is to investigate the quantitative relationship between mean patient SUVs and radiobiological parameters (such as cell survival and tumor control probability [TCP]) to facilitate quantitative prediction of tumor response based on SUVs from 18F-FDG PET before and after treatment. We investigate the same cohort of 20 esophageal cancer patients evaluated in our previous study and use the mean values of the distribution of SUV in each patient to obtain a tumor control probability curve (based on pathological response) as a function of mean ratios of SUV before and after CRT. 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 from 18F fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) before and after treatment for esophageal cancer
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