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Indium (111In) Capromab Pendetide

node metastases as well as postprostatectomy patients with a rising prostate-specific antigen (PSA), whom there is a high clinical suspicion of metastatic disease.

The kit utilized to prepare this radiotracer contains capromab pendetide, sodium acetate buffer, and a 0.22-^m filter. A portion of the sodium acetate buffer is added to a vial of indium (In-111) chloride to stabilize the radiolabel as an indium (In-111) acetate complex for subsequent reaction with the conjugated antibody. The buffered indium (In-111) acetate complex is added to the capromab pendetide and allowed to incubate for 30 minutes at room temperature. After incubation is complete, the remaining sodium acetate buffer is added to the capromab (In-111) pendetide mixture. The patient dose is drawn into a syringe that was fitted with the 0.22-^m filter. The tagged product must be used within 8 hours of preparation. A schematic representing the bifunc-tional IgG antibody modified is shown.

The patient receives an intravenous injection of 5 mCi (185 MBq). Since the radiotracer accumulates in both the bladder and bowel, patient preparation includes a cathartic laxative the night before imaging, an enema 1 hour prior to imaging, and the patient is likely to be catheterized. Images of the pelvis are taken 30 minutes after the injection to assess the blood pool distribution, and whole-body or spot images as well as specific pelvic/abdomen images are acquired between 72 and 120 hours after administration.

Indium Chloride (111In). Indium (III) chloride is a sterile, colorless solution that is isolated from the production of radiolabeled indium-111 from cadmium-112 by dissolution in hydrochloric acid solution (0.05 M) and has a pH of 1.4. It is primarily used to radiolabel pharmaceuticals such as monoclonal antibodies and peptides that are used for cancer imaging.

Indium (111In) Oxyquinoline. Indium (111In) oxyquinoline (Indium [111In] oxine) is formed by adding the required amount of 8-hydroxyquinoline sulfate to indium (III) chloride (111In). Other ingredients include polysorbate 80 as a stabilizer and HEPES buffer to adjust the pH range to 6.5 to 7.5. The structure of indium (111In) oxyquinoline is shown.10

This radiochemical is indicated for the preparation of patient-specific radiolabeled leukocytes to assess the presence or absence of a suspected infection that is unable to be confirmed by other imaging modalities. Approximately 50 mL of a patient's blood is drawn. The blood will be processed to separate the leukocytes from the plasma and other cellular components. The leukocytes will be incubated with indium (111In) oxyquinoline for 20 minutes, washed with saline, re-suspended in the patient's own plasma, and reinfused to the patient within 5 hours of the initial blood draw. The goal in leukocyte preparation is to achieve 200 to 500 ¡¿Ci of activity in the tagged cells. Images are acquired 2 to 48 hours after reinjection of the radiolabeled cells, allowing the cells to localize at the suspected site of infection.

Indium (111In) Pentetate. Indium (111In) pentetate is formed by adding the required amount of calcium or sodium pentetate (DTPA) to the indium (111In) chloride and adjusting the pH to 7 to 8 with sodium hydroxide and/or hydrochloric acid. A proposed structure of 111In-DTPA is shown on next page.11,12

This tracer is indicated for use in cisternography. The patient undergoes a lumbar puncture under sterile conditions and receives an intrathecal injection of 0.5 mCi (18.5 MBq) of indium (mIn) pentetate, which distributes into the cerebrospinal fluid (CSF). Initial images are obtained to ensure a good intrathecal injection. Images of the spinal canal and CSF spaces of the brain are acquired intermittently to assess CSF flow or leakage from the normal CSF space.

Another use for 111In-DTPA is in dual isotope gastric emptying studies. After a 6-hour fast, the patient ingests a solid meal of oatmeal or scrambled egg mixed with 1 mCi (37 MBq) of 99mTc-sulfur colloid along with a liquid meal of water mixed with 0.5 mCi (18.5 MBq) of mIn-DTPA. The patient's stomach is imaged 5 minutes after the meal as the initial gastric image utilizing appropriate camera settings to detect each isotope separately. Imaging continues every 5 to 15 minutes until the recorded activity is reduced to one half the initial gastric activity. Normal values are 50 to 80 minutes for solid meals and 10 to 15 minutes for liquid meals4; however, these values can vary based on the size and composition of the meal.5

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