Radiation dosimetry and biodistribution of ^99mTc-ethylene dicysteine-deoxyglucose in patients with non-small-cell lung cancer

^99mTc-EC-DG was prepared as described previously [9]. All clinical samples were tested for radiochemical purity (AR-2000 radio-TLC scanner; Bioscan, Washington, DC), sterility and pyrogenicity (South Texas Nuclear Pharmacy, Houston, TX).

Synthesis of EC-DG has been previously reported [9]. Briefly, EC was dissolved in NaHCO₃. To this colorless solution were added sulfo-N-hydroxysuccinimide (sulfo-NHS) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCl (EDAC) (Aldrich Chemical Co., Milwaukee, WI). d-Glucosamine hydrochloride salt (Sigma Chemical Co., St. Louis, MO) was then added. A pH of 8 was measured. The mixture was stirred at room temperature for 16 h and then dialyzed for 24 h using Spectra/POR molecular porous membrane with cut-off at 500 Da (Spectrum Medical Industries, Houston, TX). After dialysis, the product was filtered through a 0.45-µm nylon filter and then freeze-dried using a lyophilizer (Labconco, Kansas City, MO). EC-DG was labeled with ^99mTc in the presence of tin(II) chloride. ^99mTc was chelated in the EC core.

Two assays, thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC), were used to determine radiochemical purity. The TLC chromatogram (ITLC-SG) was scanned for distribution of radioactivity in a radiochromatogram scanner. Using 1 M ammonium acetate/methanol (4:1) or saline elution, the retardation factor (Rf) of ^99mTc-EC-DG was 0.8. For the HPLC assay, ^99mTc-EC-DG (20 µl, 1 mg/ml EC-DG) was loaded onto a C-18 reverse-phase column (Waters, semi-prep, 7.8×300 mm) and eluted with water at a flow rate of 0.5 ml/min. UV absorbance at 210 nm or 272 nm was used to assess the purity of ^99mTc-EC-DG; UV at 210 nm is preferred. We accept a radiochemical purity of greater than or equal to 90% as a specification for the drug product.

This study (MDACC ID01-415) was approved by the M. D. Anderson Cancer Center clinical research committee, institutional review board, radioactive drug research committee, and radiation safety committee. It was also approved by the FDA under (IND) application 63698 held by Cell>Point LLC (Englewood, CO). The phase I clinical trial (RO00-311) opened for patient accrual on 30 January 2003. All patients gave their informed consent.

Each eligible patient had to be an adult (18 years of age or older), and have a pathologic diagnosis of NSCLC with no pathologic evidence of small-cell or bronchioloalveolar carcinoma of the lung. There was no tumor stage restriction. None of the patients had undergone mediastinoscopy, fine-needle aspiration of a mediastinal node, or biopsy of a mediastinal node. None of the patients had received radiation therapy to the chest. None of the patients had received chemotherapy or other treatment for this or any other lung cancer. Pleural effusion on the most recent chest radiograph was cause for exclusion. In addition, a patient was excluded if he or she had a history of: any other primary cancer, renal insufficiency, hepatic insufficiency, insulin-dependent diabetes mellitus, or a myocardial infarction in the 6 months prior to evaluation for study participation. Patients with a history of skin cancer, carcinoma in situ of the cervix, or other tumors that had been in remission for 2 years or longer were considered eligible.

The FDA recommended the use of ¹⁸F-FDG PET findings as the gold reference standard for comparison of SPECT findings, since our subjects were to be imaged with ^99mTc-EC-DG before candidacy for definitive surgery was determined. Therefore, as part of the standard evaluation, each patient must have had, or have planned or scheduled within 14 days of consent, an ¹⁸F-FDG PET/CT scan at our institution. A CT scan of the chest with contrast agent administration had to be planned, scheduled, or to have been completed within 30 days of study consent. As part of the standard evaluation, chest radiography (with anterior-posterior and lateral views), magnetic resonance imaging (MRI) or CT scan of the brain with contrast agent administration (when clinically indicated), and a bone scan (when clinically indicated) must have been performed within 30 days prior to the patient’s consent or planned (not necessarily scheduled) within a 2-week period after consent to this study. Inability to lie flat and remain still for 45 min was an exclusion criterion.

Criteria for removal from the study included: (1) patient noncompliance with protocol requirements, (2) unacceptable adverse reaction, (3) patient’s wishes, (4) belief that the constraints of the study were detrimental to the patient’s health, and (5) inpatient status on day(s) planned for the ^99mTc-EC-DG scans.

Each patient fasted for at least 8 h prior to the administration of ^99mTc-EC-DG. The last meal before this fast was recommended to be high in protein and low in carbohydrates. Only high-protein low-carbohydrate snacks were allowed from the time of ^99mTc-EC-DG injection until all of the patient’s whole-body and SPECT study images were acquired.

Prior to ^99mTc-EC-DG administration, anterior whole-body planar transmission scans of a ⁵⁷Co sheet source placed on the posterior detector of a dual-head gamma camera equipped with low-energy high-resolution (LEHR) collimators (E.Cam, Siemens Medical Solutions USA, Hoffman Estates, IL) were acquired at a 10 cm/min scan speed both without and with the patient in between, for attenuation correction of the geometric mean regional count data from the whole-body planar ^99mTc-EC-DG scans. Approximately 925 MBq (25 mCi) of ^99mTc-labeled EC-DG was then injected as a bolus via an antecubital vein, with the patient lying on the imaging table, followed immediately by a 5-ml flush of isotonic saline solution. Simultaneous anterior-posterior whole-body planar scans were acquired immediately after injection, and then at 2, 4 and 6 h, at a scan speed of 10 cm/min. (The first four patients were also scanned at 24 h, but a statistical comparison between residence times calculated with and without the 24-h scan was performed prior to the fifth patient, which demonstrated that the 24-h scan could be eliminated.) The immediate postinjection scan was acquired prior to micturition, to ensure the total-body image at t=0 h contained 100% of the administered activity.

SPECT scanning of the thorax including the primary tumor was also performed after each of the 2-, 4- and 6-h whole-body scans. The acquisition parameters for each SPECT scan were: LEHR collimation, 120 step-and-shoot views over 360° (60 views per head), 180° noncircular orbit rotation, 128×128 image matrix with a zoom factor of 1 (4.8 mm/pixel sampling), and 26 s per view (30 min total scan time, accounting for the 4-s step time between views). Each SPECT scan was reconstructed iteratively (10 subsets, 12 iterations, and two-pixel-wide [9.6 mm FWHM] 3-D gaussian post-filtering), employing an algorithm that incorporated attenuation correction based on the CT scan derived from the PET/CT study that was manually registered to the SPECT, as well as compensation for the system resolution of the gamma camera. Both the PET/CT and SPECT scans were acquired with the patient positioned in a customized radiation therapy immobilizer, and seven fiducial markers (⁵⁷Co spot markers, visible on both SPECT and CT) were placed on the sternal notch, clavicles and sides to aid in the task of manual registration. The reconstructed slices were visually assessed for the presence of ^99mTc-EC-DG in the primary tumor.

The degree of agreement between the two imaging techniques, ^99mTc-EC-DG and ¹⁸F-FDG PET, was measured, with ¹⁸F-FDG PET results serving as the reference standard. If pathologic specimens from the thorax were obtained within 4 weeks following administration of ^99mTc-EC-DG, then that pathologic information was compared with the ^99mTc-EC-DG and ¹⁸F-FDG PET scan results. The ^99mTc-EC-DG scans were reviewed blindly and independently by a single physician certified by the American Board of Nuclear Medicine and the American Board of Radiology (as a diagnostic radiologist with special competence in nuclear radiology). The reference ¹⁸F-FDG PET scans were reviewed blindly and independently by another single physician certified by the American Board of Nuclear Medicine. The diagnostic chest CT scans to be used as reference for tumor volumes on this study were reviewed by consensus of two other physicians certified by the American Board of Radiology. Thoracic pathology findings to be used for comparison with ^99mTc-EC-DG and ¹⁸F-FDG PET scan findings in this study were reviewed by a single physician certified by the American Board of Pathology.

A tumor-to-background (T:B) ratio was calculated for each ^99mTc-EC-DG SPECT and ¹⁸F-FDG PET scan, for quantitative comparison of tumor uptake. The T:B ratio was computed from two-dimensional regions of interest (ROIs) defined on a transverse slice through the center of the tumor on each scan. A ROI was manually defined around the tumor, and then a duplicate was generated to serve as the background ROI. The background ROI was mirrored over normal tissue in the contralateral lung, unless the contralateral region included non-lung tissue (e.g., upper liver, blood pool, soft tissue), in which case a nonmirrored region in the ipsilateral lung was used instead. The T:B ratio was calculated as the ratio of the tissue count density (^99mTc-EC-DG SPECT) or average SUV (¹⁸F-FDG PET) in the two ROIs.

Radiation absorbed doses to organs from ^99mTc-EC-DG were estimated from geometric mean quantification of the total-body and organ activities in the serial whole-body planar emission images. For all imaging time points, ROIs were manually drawn around the whole body, and each organ with visible uptake, on both the anterior and posterior scans. The organs included the kidneys, liver, lungs, spleen, stomach, testes, thyroid, and urinary bladder contents. A background ROI near each organ was also defined in order to be able to subtract superimposed extra-organ activity. Total background-corrected counts within each anterior and posterior ROI were calculated, and their geometric mean was then computed [(anterior counts × posterior counts)^1/2] [15, 16]. The geometric mean of the total counts was corrected for attenuation using the measured counts from the same region in the transmission scans without and with the patient. The multiplicative attenuation correction factor for the geometric mean quantitative method is the square root of the region without-to-with count ratio, raised to the power μ₁₄₀/μ₁₂₂ to convert from ⁵⁷Co to ^99mTc attenuation, where μ₁₄₀ and μ₁₂₂ are the mass attenuation coefficients for ^99mTc and ⁵⁷Co, respectively. Finally, the attenuation-corrected counts were converted to fraction of injected activity by dividing by the administered activity and the camera sensitivity (counts per microcurie) measured with a reference source of known ^99mTc activity in a 10-ml vial acquired in each patient whole-body scan.

For all organs except the bladder, the residence time was calculated from the integral of either a single or biexponential function that had been fitted to the least-squares fit of the estimated fraction of injected activity as a function of time. The residence time for the bladder was estimated using the Medical Internal Radiation Dose (MIRD) dynamic bladder model with a 2-h voiding interval and a single or biexponential fit of the remainder of the body (total minus all organs) plus bladder contents fraction of injected activity versus time as the input function. The choice of a 2-h voiding interval was based on the requirement that the patient void immediately before each of the 2-, 4- and 6-h whole-body scans. The use of the remainder of the body plus bladder contents activity as the input function was based on the reasonable assumption that excretion of ^99mTc-EC-DG is predominantly urinary, and all EC-DG not accumulated in the organs would eventually be excreted in the urine. Radiation absorbed dose estimates were calculated using the MIRD methodology. The residence times were entered into the MIRDOSE version 3.1 personal computer program for implementation of the MIRD absorbed dose calculations, and the resulting unit absorbed dose, effective dose equivalent and effective dose estimates were tabulated [17‐20].

Blood samples (2 ml volume) were collected from all patients at approximately 5, 15, 20, 30 and 45 min, and 1, 2, 4, 6 and 24 h after injection of ^99mTc-EC-DG. A baseline sample was also drawn from each patient approximately 30 min before injection of ^99mTc-EC-DG. The times of the actual sample collections were recorded and used for data analysis. Aliquots (100 µl) were drawn from each blood sample and radioactivity was assayed using a Cobra II gamma counter (Packard Instrument Co., Meriden, CT). Data were recorded as counts per minute with decay correction, to allow assessment of biologic clearance from the blood. A calibration standard of equivalent volume was counted for conversion from counts per minute to microcuries. The data are expressed as percentage of injected dose per gram of blood.

Vital signs including heart rate, respiratory rate, blood pressure and temperature were monitored at four time points: approximately 1.5 h before and 1, 4, and 17–24 h after the bolus injection of ^99mTc-EC-DG. Samples for potassium, calcium, and magnesium levels were drawn at three time points: approximately 1 h before, 10 min before, and 80 min after the bolus injection of ^99mTc-EC-DG. Twelve-lead electrocardiography (ECG) was performed at three time points: approximately 1 h before, time 0, and 1.5 h after the bolus injection of ^99mTc-EC-DG. At the time of each ECG, patient symptoms and medications were documented as well. A board-certified cardiologist interpreted these findings. Each patient was also observed for dermatologic reactions such as bruising, allergic reactions/hypersensitivity, and wound infection immediately after injection of ^99mTc-EC-DG and then approximately 1, 3, and 5 h later. Patients were also contacted by a nurse approximately 96 h after injection of ^99mTc-EC-DG to report any adverse reactions that may have occurred in the interim.