169Yb-DTPA distribution and dosimetry in cisternography
Journal of Nuclear Medicine
Following intrathecal administration of 1 mCi '89Yb-DTPA to nine patients, spinal counts were obtained from 2 to 48 hr with a gamma camera! computer system. Utilising computer outputs, the length of the spine was divided into six equal segments approximately 2 in. wide. The counts in each segment at each time were corrected for the surrounding blood background and con verted to the percent of administered activity by reference to a standard. The cumulated ac tivity in each segment was
... by graphic integration of mean activityâ€"time curves. Ab sorbed radiation doses were computed for cylin drical geometry utilizing appropriate reduction coefficients for the dose contribution from elee trons. Maximum doses to the surfaces of the cord and nerve roots are 31 ± 18 and 46 ± 20 rads, respectively, for 1 mCi '69Yb-DTPA admin istered. By a depth of 0.01 cm, the thickness of the pia, these doses decrease to the average values of S ± 3 and 8 ± 3 rads, respectively. Surface and average doses to the cord and nerve roots from intrathecal administration of 400 @@Ci 169Yb-DTPA are about the same as those from 100 @sCi '311-IHSA.