tin-117m

Tin-117m is a metastable radioisotope of tin with unique physical properties, including emission of low-energy conversion electrons (~140 keV) and 159 keV gamma photons[1][2]. The conversion electrons have a very short tissue penetration (up to ~300 μm), enabling highly localized radiation therapy while sparing deeper tissues—a distinct advantage over traditional beta emitters, which have much longer radiological path lengths[1][2]. Tin-117m decays with a 13.6–14.5 day half-life, providing a sustained therapeutic effect without excessive persistence in the body[1][2]. It is used primarily as a radiopharmaceutical for targeted radiation therapy, with two main clinical applications: (1) as a bone-seeking agent for palliative treatment of painful bone metastases (tin-117m-DTPA), and (2) as a colloid (tin-117m-HTC, Synovetin OA) for radiosynovectomy in osteoarthritis and other inflammatory joint diseases in veterinary medicine, with early-stage human trials underway[1][5]. The mechanism of action centers on apoptosis of target cells (e.g., synoviocytes, macrophages, bone metastatic tumor cells) due to DNA strand breaks induced by the conversion electrons, resulting in reduced inflammation and pain[1]. Its gamma emission also allows for imaging with standard gamma cameras, facilitating dosimetry and real-time monitoring of drug distribution[2]. Production of tin-117m has evolved, overcoming earlier supply challenges, and it is now routinely produced at reactor and cyclotron sites for clinical and research use[2]. Tin-117m is not yet approved for human use in most indications but is marketed for veterinary use as Synovetin OA[5].

Brand names

Synovetin OA

Other names

Tin-117mTin117mTin 117mTin-117m-DTPATin117m-DTPATin 117m-DTPASn-117m-DTPASn117m-DTPASn 117m-DTPATin-117m HTCTin117m HTCTin 117m HTC