Using Pre-radiation PET Parameters to Predict Survival in Adenocarcinoma of the Pancreas Treated With Gemcitabine and Single Fraction Stereotactic Body Radiation Therapy

Abstract

Although positron emission tomography (PET) scanning has been influential in radiation treatment planning and target delineation, tumor metabolic activity has not been studied as a prognostic factor in predicting individual patient outcomes in pancreatic cancer. In a cohort of 35 patients treated with stereotactic body radiation therapy (SBRT) we analyzed whether pretreatment PET scan parameters could predict for patient survival. This study consists of 35 patients with pancreatic cancer (29 locally advanced and 6 metastatic disease) who had a pre-treatment PET scan and at least 4 months of follow-up. All PET scans were carried out on our GE Discovery-ST CT-PET scanner. PET images were imported into RT_Image (an application developed in our laboratory) for analysis. Pancreatic tumor volume, Maximum SUV, Mean SUV, Minimum SUV and integrated SUV over the tumor volume were calculated for each patient. Survival times from date of pathologic diagnosis were available for all patients. Stereotactic radiation doses of 25 Gy in a single fraction were administered. Among the various PET parameters, maximum SUV (SUVmax) demonstrated the greatest correlation with patient survival. Patients were sorted into two groups based on their SUVmax values. The Hi-SUV group consisted of patients with SUVmax values above the median and the Low-SUV group consisted of patients with SUVmax values below the median. Mean survival from diagnosis was 221 days (stdev 112) in the Hi-SUV group and 469 days (stdev 267) in the Low-SUV group (p value of 0.12 by t-test). Kaplan-Meier survival curves for all patients (Figure 1-Left) and locally advanced patients only (Figure 1-Right) are below. Neither reached significance by log-rank testing (p = 0.63 and 0.20 respectively). Our preliminary data demonstrates a trend between greater maximum SUV on pre-treatment PET scan and a reduction in overall survival. A larger sample size and longer follow-up will be available at time of presentation.