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 hemopoetic 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.)