Adjustment to radionuclide angiogram dose based upon patient's physical parameters

Objective: The standard 30-mCi technetium-99m (^99mTc) equilibrium radionuclide angiogram (RNA) dose for evaluating cardiac function has long been a problem in two respects: (1) unnecessarily high doses in smaller patients and (2) poor count statistics in larger patients. To rectify these problems, a dose chart was created based on height, weight, and gender to assist in the dispensing of an appropriate RNA dose. Methods: The chart created is based on the 1983 Metropolitan Weight and Height Tables, which state the normal ranges of weight for men and women according to their respective heights. The 30-mCi dose was used for this normal range, and 1 mCi was added or subtracted for every 10-pound deviation from this range. We prospectively applied our chart to 91 patients and calculated the counts/pixel within the left ventricular region. The study group was divided into three groups: (Group A) patients who received 30 mCi (52 ± 11 counts/pixel, n = 32), (Group B) patients who received less than 30 mCi (56 ± 8 counts/pixel, n = 28), and (Group C) patients who received greater than 30 mCi (54 ± 12 counts/pixel, n = 31). We retrospectively identified 12 patients (Group D) who received the standard 30-mCi dose, but would have received a reduced dose if our chart had been used. Results: There was no significant difference (p = 0.22) in counts/pixel among these three groups despite a very significant difference (p = 0.001) in weight. Image quality remained consistently good throughout the study. In contrast, Group D had significantly higher counts per pixel (78 ± 17 counts/pixel, p = 0.001) when compared to the other groups, indicating a need for dose reduction. Conclusions: These data clearly demonstrate that dosage adjustment by our chart avoided excess radiation in thin patients and ensured adequate counting statistics in heavy patients.