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FDG-PET Background Definition with the Use of Differential Uptake Volume Histograms for Rectal Cancer Patients

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J Schneider

J Schneider*, R Lisbona , M Hickeson , G Chausse , N Tomic , T Vuong , F De Blois , J Seuntjens , S Devic , McGill University, Montreal, QC


TH-AB-FS4-3 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: Four Seasons 4

Purpose: The goal of this study is to develop and test a new background definition methodology for use with FDG-PET/CT data. We utilize the analytical decomposition of differential uptake volume histograms (dUVHs) obtained from FDG-PET/CT data to determine patient-specific backgrounds.

Methods: This is a retrospective study of 20 histo-pathologically confirmed pT3N0 rectal adenocarcinoma patients. They underwent FDG-PET/CT scans for staging prior to pre-operative endorectal brachytherapy. Post-surgery pathology results determined that half of the patients had a complete response to brachytherapy (pT0N0) whereas half had minimal response (pT3N0). Uptake values (Bq/mL) were sampled on PET images using co-registered PET/CT images. Regions of interest (ROI) were defined to contain both tumor and healthy rectal tissue (excluding air/gas/feces). These ROIs were sampled to create a dUVH for each patient which was then decomposed into the minimal number of Gaussian functions.

Results: Each patient’s dUVH was normalized by the value of the lowest uptake peak fit to convert to signal (S) to background (B) ratio (S/B) values. This follows the assumption that this corresponds to the glucose uptake of healthy rectal tissue. The maximum S/B value ((S/B)max) was determined for each patient. It was found that for those patients that completely responded to radiation (pT0), the average (S/B)max value (10.1±0.8) was significantly higher than non-responders (pT3; 5.6±0.8) (determined via two-sample paired t-test with p<0.00001)

Conclusion: This methodology of dUVH analysis was originally developed to extract biological sub-volumes (corresponding to glycolytic variations) within tumors. The results obtained here suggest a variation of this methodology can assist in the definition of healthy tissue background for PET. Furthermore, it applies to unpaired organs, which enables dUVH analysis of sites without a healthy, contralateral organ to sample. Finally, these (S/B)max values can potentially provide a prognostic factor in predicting a tumor’s response to radiation, enabling patient-tailored treatment strategies.

Funding Support, Disclosures, and Conflict of Interest: JS acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290).

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