Direct, In Vivo Calibration Measurement of ~(241)Am in the Axillary Lymph Nodes Using the Livermore Thoracic Phantom

摘要

The Livermore Torso Phantom, the consensus calibration phantom for measuring internally depositedradioactive materials in the lungs, liver and tracheo-bronchial lymph nodes, has been modified for calibratingdirect, in vivo measurements of ~(241)Am in the axillary lymph nodes. The axillary lymph nodes may containradioactive material mobilized from a wound in a finger or hand which may confound results of a direct, in vivomeasurement of the lungs or liver. Modifications to the Livermore Torso Phantom involved milling a pair ofparallel, flat bottom cylindrical holes into the left and right shoulders (below the humeral head) for inserting apair of solid 1.40 cm diameter cylindrical rods made of a 100% muscle tissue substitute. A precisely knownquantity 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 andthe combined Level II +III axillary lymph nodes reported in the literature. Discrete calibration measurementswere performed for axillary lymph nodes located in the right and left side of the thorax using a pair of 3000 mm~2high resolution germanium detectors . The efficiency for measuring ~(241)Am in the right and left lymph nodes is2.603 % ± 0.0342 % and 5.453 % ± 0.0716 %, respectively. Activity deposited in the right and left axillarylymph nodes was found to contribute 0.183% and 0.289 %, respectively, to a lung measurement and 0.013 % and0.002 %, respectively, to a liver measurement. Thus, results of this research demonstrate that ~(241)Am deposited inthe axillary lymph nodes has the potential to confound direct, in vivo measurements of activity in the lung orliver.