Dosimetry of several DTPA radiopharmaceuticals in cisternography

Previously published biologic distribution and clearance data for 169Yb-DTPA in cisternography were utilized to obtain effective spinal segment clearance data for six other easily dhelated radionuclides: 99mTc, 113mIn, 111In, 67Ga, 51Cr, and 203Pb. Absorbed radiation doses to the spinal cord and nerve roots were calculated for each radioactive DTPA compound, employing appropriate cylindrical geometry and reduction coeffients for the dose contributions from the electrons of each radionuclide. Doses are maximal at the surface and decrease rapidly with distance from the surface. The relative useful photon flux from each DTPA radiopharmaceutical for approximately the same average absorbed radiation dose to the spinal cord was determined. The results indicate that 111In and 203Pb should be considered as possible radionuclide tags for DTPA cisternographic imaging.