Biodistribution of Sn-117m(4+)DTPA for palliative therapy of painful osseous metastases.

Abstract

Tin-117 has certain physical characteristics (half-life of 13.6 days, low-energy-conversion electrons, gamma photon of 158.6 keV) that suggest that it may be a favorable agent for radionuclide therapy. It has been shown in animal models that Sn-117m in the chemical form Sn(4+)diethylenetriaminepentaacetic acid localizes selectively in bone. The authors therefore studied its whole-body distribution in 10 patients to obtain absorbed dose estimates for therapy. The results showed that more than 50% of the administered activity was absorbed in the bones of patients with metastatic carcinoma. Retention was determined primarily by radioactive decay. For adult men, the radiation absorbed dose estimate averaged 54.8 mGy/MBq (203 rad/mCi) to bone surfaces and 6.1 mGy/MBq (22.6 rad/mCi) to the red marrow. All other tissues received less than 1/10 of the dose received by red marrow. These results suggest that a clinical therapeutic trial should be attempted.

The role of electron-emitting radiopharmaceuticals in the palliative treatment of metastatic bone pain and for radiosynovectomy: applications of conversion electron emitter Tin-117m

“…At this time somewhat limited but sufficient clinical experience has been obtained with this compound (Atkins et al, 1993;Atkins et al, 1995;Krishnamurthy et al, 1997;. Its physical characteristics are very favorable.…”

“…Further studies (Oster et al, 1995) showed that its behavior mimicked that of Tc-99m MDP in certain pathological conditions. The biodistribution was studied in a group of patients with advanced metastatic disease from various primary malignancies (Atkins et al, 1993). The disappearance rate from blood appeared to be considerably slower than other bone agents and urinary excretion slower.…”

“…However, because of its rather long physical half-life relative to these biologic parameters, this is not a problem for radiation absorbed dose estimates. Once localized in bone, the Sn-117m appears to remain fixed with no or extremely slow release other than through physical decay (Atkins et al, 1993;Atkins et al, 1995). Approximately 70% is taken up by bone, but this is highly variable and depends on the extent of disease.…”

Therapeutic Radionuclides: Making the Right Choice

“…Introduction of "Sr has catalyzed the development of newer competitive agents that may offer improvements in efficacy or reduced myelosuppression. The radionuclides under investigation include pemitters la6Re (31) and 153 Sm (32), and the conversion-electron emitter tin-1 17m (33,34). Physical and nuclear properties of the various radionuclides for bone pain palliation therapy are summarized in Table 4.…”

“…The energy of the beta particles seems t o be an important factor because the dose to the marrow depends on the range of penetration of the particles into the marrow from the deposited radioactivity on t o the bone surfaces. In this respect, '""Sn may offer a distinct advantage because of the discrete limited range (0.2-0.3 mm) of its conversion electrons in tissue (33)(34)(35). It remains t o be seen which one of these agents eventually will become the agent of choice.…”