Dosimetric consequences of radiopharmaceutical infiltrations.
OBJECTIVE
Little is known about the time-related biologic behavior of radiopharmaceutical misinjections. Such inadvertent tissue infiltration of such injections may not only adversely affect a scheduled test or cause some discomfort, but potentially could produce tissue damage. Radiopharmaceutical infiltrations were assessed in a rat model.


METHODS
Particulate and nonparticulate radiopharmaceuticals were injected subcutaneously or intradermally into an anesthetized shaved rat model. The rate of release of the nine infiltrations per radiopharmaceutical per injection type were measured from computer data acquired with a gamma camera up to 24 hours after administration. These data were used for dosimetry determinations.


RESULTS
When injected subcutaneously, the particulate radiopharmaceutical, technetium 99m (99mTc) albumin microspheres, exhibited essentially no movement, and the soluble agents showed a biexponential release pattern. The rate of release was similar for 99mTc methylene diphosphonate (99mTc MDP) and for 67Ga citrate (67Ga), whereas thallous chloride (201Tl) exhibited the slowest release pattern. The average effective half-lives (T1/2 av-eff) were 78.3 minutes, 76.1 minutes, and 268.4 minutes, respectively. When injected intradermally, the nonparticulates exhibited a triexponential release pattern; MDP showed a more rapid release (T1/2 av-eff, 50 minutes) and 201Tl showed the slowest (T1/2 av-eff, 491.2 minutes). Absorbed doses were calculated using conventional medical internal radiation dose (MIRD) methodology for small unit density spheres. The absorbed dose was greatest for a 201Tl infiltration. A 201Tl infiltrate of 1 mCi per gm of tissue is capable of producing radiation-absorbed doses greater than 500 rads. Additional studies were performed with heat, hyaluronidase, and volume dilution in an attempt to accelerate the rate of release of 201Tl. Local heat application proved to be more efficient than volume change or hyaluronidase application.


CONCLUSIONS
These data indicate an insignificant skin radiation burden from the majority of nonparticulate infiltrated radiodiagnostic agents. Thallium 201, however, has the potential to produce significant radiation burdens when infiltrated at high specific activity. Actual human infiltration release rates may differ because of variants in blood flow and assumed infiltration volume relative to the animal model.
Castronovo
F P
FP
Department of Radiology, Massachusetts General Hospital, Boston.
McKusick
K A
KA
Strauss
H W
HW
D000818:Animals; D002951:Citrates / Q000008:administration & dosage / Q000493:pharmacokinetics; D019343:Citric Acid; D005119:Extravasation of Diagnostic and Therapeutic Materials; D005710:Gallium Radioisotopes / Q000008:administration & dosage* / Q000493:pharmacokinetics; D006801:Humans; D007271:Injections, Intradermal; D007279:Injections, Subcutaneous; D008297:Male; D008863:Microspheres; D011829:Radiation Dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D013668:Technetium Tc 99m Aggregated Albumin / Q000008:administration & dosage* / Q000493:pharmacokinetics; D013669:Technetium Tc 99m Medronate / Q000008:administration & dosage* / Q000493:pharmacokinetics; D013793:Thallium / Q000008:administration & dosage / Q000493:pharmacokinetics; D013794:Thallium Radioisotopes / Q000008:administration & dosage* / Q000493:pharmacokinetics
D002951:Citrates; D005710:Gallium Radioisotopes; D013668:Technetium Tc 99m Aggregated Albumin; D013794:Thallium Radioisotopes; D019343:Citric Acid; C027549:thallium chloride; D013793:Thallium; D013669:Technetium Tc 99m Medronate