Feasibility study: in vivo neutron activation for regional measurement of calcium using californium 252.

The feasibility of using a collimated 252Cf neutron source to measure regional changes in skeletal calcium was tested because in vivo regional activation of diseased bone should offer advantages over the more widely reported total-body calcium measuring techniques. Regional activation allows examination of discrete regions where the greatest changes in calcium content occur. Additionally, a simpler radiation facility is required for regional studies. Using a 5.5-mug 252Cf source, thermal neutron flux and absorbed dose were measured in a tissue-equivalent phantom. Detection efficiency of 49Ca gamma rays for conditions simulating regional activation were measured using a 29-cm-diameter X 10-cm-thickness sodium iodide detector. These in vitro measurements indicate that a collimated 252Cf source can be used for regional neutron activation of the lower spine and legs. Preliminary calculations indicate that a 1-3-mg source provides adequate count rates for statistical accuracy with a bone marrow dosage acceptable for human patients and normal subjects.