Radiation Oncology/Unsealed sources

See also: Isotopes used in Radiation Oncology For bone metastases These have usefulness in treating blastic bone lesions (basically anything that lights up a bone scan). The dose limiting toxicity is bone marrow. Observe platelet counts. Please see the bone metastases page Phosphorus 32 - beta emitter Gets taken up in bone Not commonly used Strontium 89 (Metastron) - beta emitter Calcium analog, gets taken up in bone Long half life (50.5 days physical half-life) Usual dose 4 mCi (supplied as a 4 mCi vial) May also be dosed at 0.040-0.060 mCi/kg Samarium 153 (Quadramet) - beta and gamma emitter Bound to a tetraphosphonate, which gets taken up in area of active Usual dose 1 mCi/kg (may use 0.5 mCi/kg) Short half life (about 3 days) Can repeat dose after about 6-8 weeks Lowest effective range (compared to Sr and P) and thus lower bone marrow toxicity Can be used for imaging also due to its photon component P-32 ovarian cancer endometrial cancer uterine papillary serous carcinoma pancreatic cancer Pure Beta emitter Energy: 1.71 MeV and 0.69 MeV electrons Average tissue penetration: 1.4-3mm T ½ : 14.3 days Benefit: no photon contamination Typical dose: 10-15 mCi 10 mCi gives equivalent of 30Gy to the peritoneum Distribution Test intraperitoneal distribution with T-99mc prior to treatment Inhomogeneous dose distribution. Mainly absorbed in the peritoneal surface Some enters systemic circulation via lymphatics and is removed by the liver LNs receive low, subtheraputic doses Little hemopoietic toxicity Peripheral blood dose: 1.2 cGy Bone marrow dose: 6 cGy Research Experimental antibody based methods - alpha emitters At the ITU (Institute for Transuranium Research; website) work is being done on Alpha-Immunotherapy, an experimental method using antibodies bound to alpha isotopes. Bismuth-213 is one of the isotopes which has been used. This is made by the alpha decay of Ac-225. The generation of one shortlived isotope from longer lived isotope is a useful method of providing a portable supply of a shortlived isotope. This is similar to the generation of technetium-99m by a technetium cow. The actinium-225 is made by the irradation of radium-226 with a cyclotron. Guidelines see also: Guidelines at Bone metastases Reviews Samarium-153: 2004 PMID 16985930 -- Full text "Overview of Samarium Sm 153 Lexidronam in the Treatment of Painful Metastatic Bone Disease" (Sartor O, Rev Urol. 2004;6 Suppl 10:S3-S12.)