Direct, In Vivo Calibration Measurement of Am in the Axillary Lymph Nodes Using the Livermore Thoracic Phantom

The Livermore Torso Phantom, the consensus calibration phantom for measuring internally deposited radioactive materials in the lungs, liver and tracheo-bronchial lymph nodes, has been modified for calibrating direct, in vivo measurements of Am in the axillary lymph nodes. The axillary lymph nodes may contain radioactive material mobilized from a wound in a finger or hand which may confound results of a direct, in vivo measurement of the lungs or liver. Modifications to the Livermore Torso Phantom involved milling a pair of parallel, flat bottom cylindrical holes into the left and right shoulders (below the humeral head) for inserting a pair of solid 1.40 cm diameter cylindrical rods made of a 100% muscle tissue substitute. A precisely known quantity of radioactive material was sealed in a 1 cm diameter, 2.54 cm deep well located at the end of each rod. The location adopted for the simulated lymph nodes was determined according to the position of the Level I and the combined Level II +III axillary lymph nodes reported in the literature. Discrete calibration measurements were performed for axillary lymph nodes located in the right and left side of the thorax using a pair of 3000 mm high resolution germanium detectors . The efficiency for measuring Am in the right and left lymph nodes is 2.603 % ± 0.0342 % and 5.453 % ± 0.0716 %, respectively. Activity deposited in the right and left axillary lymph nodes was found to contribute 0.183% and 0.289 %, respectively, to a lung measurement and 0.013 % and 0.002 %, respectively, to a liver measurement. Thus, results of this research demonstrate that Am deposited in the axillary lymph nodes has the potential to confound direct, in vivo measurements of activity in the lung or liver.