Radiation Biology

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SU_42_2422 - Comparison of the Use of MRI and 18F-FDG PET/CT in Tracking Tumor Progression and Treatment Efficacy in Mouse Models

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Comparison of the Use of MRI and 18F-FDG PET/CT in Tracking Tumor Progression and Treatment Efficacy in Mouse Models
J. Panetta1, D. Cvetkovic2, and C. M. C. Ma2; 1Fox Chase Cancer Center, Philadelphia, PA, 2Temple University, Philadelphia, PA

Purpose/Objective(s): Noninvasive preclinical imaging is an important tool used in longitudinal studies that track the progression of small animals for the study of emerging treatment techniques. The purpose of this study is to compare two commonly used methods of tumor monitoring in mice: MRI and 18F-FDG PET/CT. It is hypothesized that while MR imaging allows for less inter-observer variability and more precise tracking of tumor volume,18F-FDG PET/CT imaging accounts for tumor changes that are non-anatomic (e.g. metabolic changes, necrosis) and may lead to useful metrics for tumor progression.

Materials/Methods: Nude mice (n>30) were injected subcutaneously into their flanks with human prostate cancer (PC-3) cells and allowed to grow tumors. These mice were divided into three groups, as part of an ongoing study to test the effectiveness of radiodynamic therapy: a control group that was untreated, a group treated with radiation therapy, and a group injected with 5-aminolevulinic acid and treated with radiation. Each mouse underwent weekly MRI and 18F-FDG PET/CT scans. The MRI scans were conducted under ketamine anesthesia with a GE Signa 1.5 T MR scanner using a fast T2-weighted sequence, while the 18F-FDG PET/CT scans were conducted under isoflurane anesthesia with a Sofie-Biosciences G8 small animal PET/CT scanner, and involved an injection of ~80 µCi of 18F-FDG and a 60 minute period of rest between injection and scanning. MR images were analyzed using a program designed in GNU Octave and tumors were contoured using a connected thresholding algorithm based on the contrast differences between the tumor and surrounding background. PET/CT images were analyzed using VivoQuant software using a connected thresholding algorithm based on fixed percentages of the maximum activity within the tumor.

Results: Tumor volumes measured using MR and PET/CT images differed significantly, with volumes measured using PET/CT typically smaller than those measured using MRI. Additionally, changes in tumor volume for each mouse, normalized to the maximum tumor volume, differed significantly between modalities, indicating volumes measured using PET/CT and MRI could not be reliably correlated. These discrepancies varied depending on the threshold used, and increased with decreasing tumor volume. Several sources of this discrepancy are noted, including the uncertainty in FDG administration, statistical uncertainty in the voxel values in PET images, and the limited spatial resolution of PET/CT. Additionally, use of PET/CT allowed for contouring around necrotic structures within the tumors that could not be visualized on MRI.

Conclusion: Imaging using PET/CT and MRI leads to difference in tumor volume and tumor progression in the mice studied in this work, indicating that these modalities provide different information regarding the tumors. This work encourages further efforts to determine the value of 18F-FDG PET/CT in the tracking of tumor progression.

Author Disclosure: J. Panetta: None. D. Cvetkovic: None. C. Ma: Employee; Fox Chase Cancer Center. Committee Member; AAPM.

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