Samarium-153

Fig. 1
Samarium-153 - UW-L Brachy Course Variable uptake of 153Sm-EDTMP in metastatic osteosarcoma: anterior and posterior gamma camera imaging 24 hours after administration of 3 mCi/kg. Note the more avid radioisotope uptake of the left chest mass adherent to the pericardium compared with the spine and right renal metastases.





Sm-153
The structural formula of samarium lexidronam pentasodium is:
Fig 2:
The structural formula of samarium lexidronam pentasodium


Relevant historical data: In 1953, Samarium was discovered spectroscopically by Swiss chemist Jean Charles Galissard de Marginac by its sharp absorption lines in didymium, and isolated in Paris in 1879 by French chemist Paul Emile Lecoq de Boisbaudran from the mineral samarskite. Before the 1950s, samarium had no commercial uses in pure form. This soon changed when samarium was used as a mixture in a by-product named "Lindsay Mix". This by-product was a fractional crystallization purification of neodymium. This material is thought to have been used for nuclear control rods in some of the early nuclear reactors. Now a similar product goes under the name "Samarium-Europium-Gadolinium" concentrate. Samarium-153 is a radioactive form of the rare metallic element samarium. It is a type of radioisotope of the lanthanide element Samarium with carrier EDTMP (ethlyene diamine tetramethlene phosphonate).
Chemical/Radioactive Composition: Symbol: Sm
Atomic Number: 62 (# of Protons)
Mass Number: 153 (# of Protons + # of Neutrons)
Energy Characteristics: Beta: 640 keV 30% Abundance
Beta: 710 keV 50% Abundance
Beta: 810 keV 20% Abundance
Gamma: 103 keV 29% Abundance
Average Beta Particle Energy: 233 keV
Exposure Rate Constant: 0.09028 R/hr at a distance of one meter from one curie point source
Gamma-ray constant is 0.46 R/mCi-hr at 1 cm (1.24 * 10^-5 mSv/MBq-hr at 1meter)
Half-life Properties: 46.3 hours (1.93 days)
Forms available for use: Quadramet is radioactive samarium-153 complexed with EDTMP. It is supplied frozen in a single-dose glass vial containing 3 mL with 5550 MBq of Samarium-153 at calibration.
HVL in lead: 0.10 mm
Measurement/Calibrations/QA: Samarium-153 activity at calibration is 5550 MBq when supplied frozen in a single dose glass vial containing 3 mL of Quadramet.
There was a study conducted that attempted to quantify the radiation dosage to individual lesions on a macroscopic and microscopic level. A gamma camera was used as a quantification technique for Sm-153. The accuracy of this technique was achieved by using a realistic phantom. Sm-153 activity of 25 MBq (volume of <3mL) was measured accurately (error <2%) in a source calibrator (Picker Isotope Calibrator). The syringe was imaged in a water-equivalent plastic block at a depth of 50mm.
After speaking with my physicist, she ran through the procedure of calibrating Sm-153. Nuclear medicine is where you would calibrate this source. First of all, before using the dose calibrator you must order from the manufacturer since Sm-153 is a beta emitter. Calibrators only read for photons not electrons. Once you have the calibration from the manufacturer, you can match it to your dose calibrator. Geometry must be the same for this to work.
Used in formula/calculation: After administration of Sm-153, some 41 patients underwent certain calculations attained for accrued activity integral in the cortical and trabecular bone using this following equation.
A= accrued activity A(t)= retained activity in each structure in various times...=intermediate terms between 1 and 24 hours
Lambda= the samarium -153 disintegration constant
Reference to the complete equation is listed below.
Uses in Radiation Oncology: This substance is used in the treatment of bone cancer and bone metastases. It collects in bone where it releases radiation that can kill tumor cells. Patients with bone cancer often undergo severe pain, and this isotope can relieve some of this discomfort. It is injected in the form of a drug known as Quadramet.
Treatment Planning: Samarium -153 is injected in the vein and is distributed throughout the body. Samarium-153 EDTMP is in areas where cancer has invaded the bone. This radioisotope once in bone emits beta particles which kill nearby cancer cells. Usual activity for this kind of treatment is 1 mCi/kg. Various authors describe the radiation absorbed dose in the marrow to be between 230 and 590 cGy with this activity. The pain begins to improve within the first week and effects may last for several months for most people. This radioisotope is commonly used for lung, prostate, breast, and osteosarcoma cancers. The typical dose is 70mCi, normally 20-40 MBq/kg of patient's body weight.
One other interesting fact: Samarium-153 EDTMP treatment was first described in 1989, and it was first approved for clinical use in the USA in 1997. Another fact I found in my researching is that Samarium-153 allows for the option of visual evaluation of agent uptake and distribution, which is not available with Strontium-89.


Links:
http://www.scielo.br/pdf/rhc/v59n6/a03v59n6.pdf ( View the calculation Page 3)
References:
http://www.ornl.gov/sci/isotopes/r_sm153.html
http://en.wikipedia.org/wiki/Samarium
http://www.rxlist.com/cgi/generic/quadramet.htm
http://www.cytogen.com/professional/quadramet/pi.php
http://www.iem-inc.com/toolgam.html
http://www.chemistryexplained.com/elements/P-T/Samarium.html
http://www.scielo.br/pdf/rhc/v59n6/a03v59n6.pdf
http://en.wikipedia.org/wiki/Quadramet
http://www.geocities.com/jimgreen3/samarium.html
http://www.mcg.edu/radscape/CaseStudies/Fall%202003/Prostate%20Cancer%20Aaron/Case.htm
http://jnm.snmjournals.org/cgi/reprint/39/12/2110.pdf

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