Samarium-145: A new brachytherapy source

A new radiation source has been produced for brachytherapy, with radiation energies slightly above those of ¹²⁵I, and a T_1/2 of 340 d. This source, ¹⁴⁵Sm, is produced by neutron irradiation of ¹⁴⁴Sm (96.5% enriched). Decay is by electron capture with 140 K X-rays per 100 disintegrations in the energy region between 38-45 keV, plus 13 gamma -rays at 61 keV. These sources are encapsulated in Ti tubes, approximately 0.8 mm*4.5 mm, and have been developed for temporary implantation in brain and ocular tumours. The 38-61 keV photons should make such sources easy to shield, while providing a dose distribution from source arrays somewhat more homogeneous than that from ¹²⁵I. In addition, the 340 d half life of ¹⁴⁵Sm permits its use for times significantly longer than that of 60 d ¹²⁵I. While the ¹⁴⁵Sm sources have been designed primarily for implantation in a brain tumour, they should be useful for almost any conventional brachytherapy application.