Elsevier

Clinical Positron Imaging

Volume 3, Issue 5, September–October 2000, Pages 189-196
Clinical Positron Imaging

Original article
Correlative Whole-Body FDG-PET and Intraoperative Gamma Detection of FDG Distribution in Colorectal Cancer

https://doi.org/10.1016/S1095-0397(00)00052-2Get rights and content

Abstract

Purpose: 18F-Fluorodeoxyglucose-positron emission tomography (FDG-PET) is the superior imaging modality for detection of primary and recurrent colorectal cancer compared to magnetic resonance imaging (MRI) or computerized tomography (CT). We investigated the feasibility of developing intraoperative procedures for detection of FDG in tumor deposits in order to assist the surgeon in achieving an optimal reduction of tumor burden.

Procedures: Fourteen patients (45–83 years of age) were scanned using FDG-PET followed by Gamma Detection Probe evaluation at laparotomy. One patient did not have a pre-operative FDG-PET scan. The collimated detector probe contained a CdZnTe crystal (7mm diameter × 2mm thick). We used a lower window setting of 200 KeV and an open upper window setting. Fasted patients were given an IV bolus of FDG (4.0–5.7 mCi) 15–20 minutes prior to preparation for surgery. Catheterization and the diuretic Lasix were used to remove FDG activity from the bladder. The time from FDG injection to intraoperative GDP data acquisition varied from 58–110 minutes.

Results: In all patients, the GDP detected background activity in normal tissues (aorta, colon, liver, kidney, abdominal wall, mesentery, and urinary bladder). The GDP correctly identified single or multiple tumor foci in 13/14 patients as noted by an audible signal from the control unit (3 S.D. above counts obtained from normal tissues). These tumor foci corresponded to regions of high FDG uptake as seen on FDG-PET scans. The one case that the GDP did not localize was a recurrent mucin pseudomyxoma-producing tumor (acellular, mucinous deposits). Ex vivo GDP evaluations demonstrated significant tumor:normal adjacent tissue activity (audible signals in 6/6 tumor samples tested).

Conclusions: These data demonstrate that tumors identified from pre-operative whole-body PET scans can be localized during surgery utilizing a gamma probe detector and FDG.

Introduction

The recurrence rate for colorectal cancer after surgical resection of primary tumor is approximately 40%.1 Of these, 25% are local recurrences and result from failure of pre-operative detection or sub-optimal clearance of margins at surgery.2, 3 The majority of other recurrences occur at distant sites in the liver, lungs, and pelvic organs.4 These recurrences often involve lymph nodes in areas of the gastrohepatic ligament, retroperitoneal region, root of the small bowel mesentery, and lateral pelvic wall. Despite advances in pre-operative use of computerized tomography (CT) for diagnosis of abdominal disease, a significant number of patients are incorrectly diagnosed and, ultimately, are found to have additional recurrences.5

In recent years, more sensitive diagnostic methods have become available to surgeons to aid in their assessment of extent of disease. In this regard, our institution pioneered the use of radioimmunoguided surgery (RIGS) for use in surgical oncology settings. We have conducted numerous studies using gamma detection probes to localize tumors targeted by tumor antigen-specific radiopharmaceuticals labeled with 125I t1/2 = 60 d.6 Patients who had all RIGS positive tissue removed surgically had a better survival rate than those patients whose tumor tissues could not be fully extirpated.7

More recently, studies have demonstrated that 18F-Fluorodeoxyglucose-positron emission tomography (FDG-PET) is superior to CT and magnetic resonance imaging (MRI) in its ability to more accurately stage patients presenting with recurrent colorectal adenocarcinoma.8, 9, 10, 11 In our recent experience, we have utilized whole-body FDG-PET to evaluate the presence and extent of colorectal cancer in over 100 patients.12 These studies have allowed us to assess the extent of disease more accurately and make better therapeutic decisions.

The aim of the present study was to utilize the favorable pharmacological properties of FDG (preferential tumor localization and retention vs. rapid organ clearance) to develop sensitive and specific methods to identify and differentiate tumor deposits from normal tissue using intraoperative detection techniques.

This study consisted of two parts. First, a phantom study was conducted to evaluate instrument performance prior to use in an operating room environment. The second phase of the study was conducted in a surgical setting with cancer patients to determine if tumors labeled with FDG can be located intraoperatively with a gamma detector probe.

Section snippets

Materials and Methods

Fifteen patients (6 females, 9 males) between the ages of 45–83 years (mean 61) were enrolled. Six of these patients were diagnosed with primary colon adenocarcinoma and 9 had recurrent disease. Whole-body FDG-PET scans were performed on all but one of the patients prior to surgery. The time interval between FDG-PET scans and surgery varied from 1 to 32 days. The FDG used in this study was produced under Good Manufacturing Practices (GMP) conditions at cyclotron facilities located at Kettering

Phantom Studies

A series of organ phantom studies were conducted in order to evaluate instrument performance prior to use in the operating room environment. The first experiment was designed to examine the effects of lower energy detector window setting and shielding on probe count rates when exposed to an FDG source. As expected, adjustment of the lower window setting from 124–200 Kev resulted in nearly a 50% decrease in 2-second counts (20,000 to 10,500) without additional shielding. When the shield was

Discussion

The immediate goal of this study was to test the feasibility of localizing FDG-targeted tissue in a surgical setting using an intraoperative radiation detector probe and to verify that these tissues correspond to tumors that are identified on whole-body FDG-PET scans. Our longer-term goal is to develop the optimal combination of tumor-targeting radiopharmaceuticals and intraoperative probe technology to achieve 3 main objectives. These are: 1) identify those tumors that take up the targeting

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