Radiation Oncology/Unsealed sources

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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

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.)