Gastrointestinal Cancer

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SU_15_2152 - Size of hepatic metastases on PET/CT versus pathologic specimen: implications for radiation treatment planning

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

Size of hepatic metastases on PET/CT versus pathologic specimen: implications for radiation treatment planning
D. G. Tanenbaum1, S. Goyal2, C. Zhang3, N. T. Pfister4, N. A. Madden5, S. K. Maithel6, J. C. Landry1, and P. R. Patel1; 1Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA, 2Department of Biostatistics and Bioinformatics Shared Resource, Winship Cancer Institute, Atlanta, GA, 3Department of Biostatistics and Bioinformatics Shared Resource, Winship Cancer Institute of Emory University, Atlanta, GA, 4Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA, 5Department of Radiation Oncology, Winship Cancer Institute, Emory University, Atlanta, GA, 6Department of Surgical Oncology, Winship Cancer Institute, Emory University, Atlanta, GA

Purpose/Objective(s): The accuracy of positron emission tomography/computed tomography (PET/CT) in measuring the gross tumor volume in patients with resectable hepatic metastases is unknown. The resolution of target structures may not be as high as with other imaging techniques, however PET/CT is a common imaging technique used in the staging for many cancers. We aim to investigate the concordance between imaging and pathologic tumor size in patients with resected hepatic metastases to determine if the appropriateness of PET/CT for delineation of gross tumor volume (GTV) for radiation treatment planning.

Materials/Methods: An institutional database of patients with hepatectomies was queried for patients with metastatic disease. Patients with positive macroscopic margins (R2) were excluded from the study. Patients with pre-operative PET/CT at our institution were selected for the study. Largest tumor dimensions were obtained from each preoperative PET/CT, as well as from the postoperative pathologic tumor specimen. Statistics from the largest dimension from PET/CT minus largest dimension from pathology were calculated using a general linear regression model.

Results: The study identified 25 patients with preoperative PET/CT and gross pathologic specimen measurements. Median age in years was 59 (range 28-81). Median time in days between PET/CT and hepatectomy was 21 (range 1 – 98). The most common pathology was colorectal cancer (n=17). 21 patients had R0 margins, 4 patients had R1 margins. The median largest dimension from pathologic specimen was 4.5cm (range 1.5-12). When compared to pathologic specimen, PET/CT underestimated the tumor size by a mean of 6.5mm (95% CI: 0.14-12.9; p=0.046). Gender, pathology, number of lesions, and time between PET/CT and surgery were not found to be significantly associated with the underestimation of tumor size.

Conclusion: PET/CT demonstrated an underestimation in the determination of tumor size when compared to the gold standard of tumor specimen size on pathology. Target delineation within hepatic anatomy is challenging, and the determination of the optimal imaging for treatment planning is unknown. Our data suggest using a larger margin when using PET/CT for target delineation of hepatic metastases.

Author Disclosure: D.G. Tanenbaum: None. S. Goyal: None. N.T. Pfister: None. N.A. Madden: None. P.R. Patel: None.

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