Initial experience in the use of technetium-99 metastable hydroxymethylene diphosphonate as an alternative ventilation agent during periods of interim shortage

Sporadic supply interruptions of select radiopharmaceuticals on the global market require consideration of alternative agents to support continuity of essential nuclear medicine examinations. During an acute shortage of Xenon-133 and technetium-99 metastable (Tc-99m) diethylene-triamine-pentaacetate (DTPA), our institution used aerosolized Tc-99m hydroxymethylene diphosphonate (HDP), a radiopharmaceutical traditionally used in bone scintigraphy, in lieu of traditional ventilation agents, for two cases of suspected pulmonary embolism. Similar to Tc-99m-DTPA, Tc-99m-HDP was readily available and easily compounded in our pharmacy, and tolerated well by patients. Identical delivery equipment was used for administration of Tc-99m-HDP as that used in Tc-99m-DTPA, and thus, there was no requirement for a negative pressure room. Similar to Tc-99m-DTPA and unlike Xenon-133, Tc-99m-HDP allowed direct comparison of all 8 ventilation-perfusion images. In addition, the cost per dose of Tc-99m-HDP proved to be less than Tc-99m-DTPA. Despite these favorable characteristics of Tc-99m-HDP, our experience identified an important challenge in obtaining an optimal flux override ratio of > 3 in a reasonable time frame while obtaining ventilation and perfusion images sequentially despite reversing the imaging order in an attempt to overcome this limitation. Although our experience with Tc-99m-HDP in these two cases was favorable, more clinical experience and investigation are warranted before Tc-99m-HDP can be incorporated as a standard alternative ventilation agent.