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Photos: Strontium - 90 / Yttrium - 90 - UWL Medical Dosimetry Brachy Class 08-09
Robot manipulator holding a vial of Yttrium-90 in a hot cell. Image 1		 Figure V: Intravascular brachytherapy delivery system employing Sr-90/Y-90 seed sources. The transfer device is used to drive the sources to the lesio

Strontium - 90 / Yttrium - 90 - UWL Medical Dosimetry Brachy Class 08-09
Image 2.

Relevant Historical Data: In 1970 Adair Crawford and William Cruishank first detected non-radioactive strontium in the mineral strontianite in Scotland. Radioactive Sr-90, like many other radionuclides, was discovered in the 1940's in nuclear experiments connected to the development of the atomic bomb. (4)

Strontium-90 is a byproduct of the fission of uranium and plutonium in nuclear reactors, and in nuclear weapons. It was found in the waste. Large amounts of Sr-90 were produced during atmospheric nuclear weapons tests conducted in the 1950's and 1960's and dispersed worldwide. (4)

Sr-90 decays to a daughter element called Yttrium-90 by emmitting a beta particle <0.5MeV in energy. (5)
Chemical/Radioactive Composition: Sr 90: atomic number = 38; atomic mass 90.(8).
Chemically reactive; can create halide, oxide, and sulfide compounds

Sr-90 decays to yttrium 90 (Y-90), which in turn decays by beta radiation so that wherever Sr-90 is present Y-90 is also present. Because of the beta radiation, Y-90 poses a risk of burns to the eyes and on the skin from external exposure. (1)
Energy Characteristics: They are both beta emitters with a maximum energy of 2270 keV an average energy of 970 keV. (6). maximum energy values are 546 and 2226 keV. Sr-90 decays via -ve beta emission to Y-90, Max beta Energy= 0.546 MeV. Y-90 decays via -ve beta emission to stable Zr-90. MAx beta energy = 2.283MeV. Only small gamma radiations accompanies these dacays (9)
Exposure Rate Constant: It doesn't have an exposure rate constant. (7)
Half-life Properties: Sr-90 = 28years (3), pure Y 90= 2.67 days
Forms available for use: Sr-90 is a soft metal. It can be present in dust from nuclear fission after detonation of nuclear weapons or a nuclear power plant accident.(1). Y-90: liquid used for lymphoma salvage, Zevalin monoclonal antibody
HVL in lead: It doesn't have a HVL in lead. It's penetrability is very shallow. (7). Sr-90 =0.125 in tissue.(9)
Measurement/Calibrations/QA: The principles of Time, Distance, and shielding should be observed with all radioctive isotopes.

Y-90. Warnings The contents of the vial are intended for use in the preparation of radiolabelled monoclonal antibodies. The contents of the vial are NOT to be administered directly to patients. Adverse Reactions None known. Adequate shielding should be used with this beta-emitter, in accordance with institutional good radiation safety practices. The absorption of high energy beta particles in matter gives rise to the production of electromagnetic radiation (bremsstrahlung). This radiation is more penetrating that the beta particles which produce it. Therefore, it is essential to reduce the bremsstrahlung production to a minimum for efficient shielding against beta particles. This is done using materials of low atomic number. Plexiglass of thickness 0.1 inch will absorb all beta particles with energies up to 1 MeV.
Dosage and Administration This product is used to prepare Yttrium-90 radiolabelled monoclonal antibodies. The patient dose should be measured by a suitable radioactivity calibration system prior to administration. Directions for Preparation. Use aseptic technique and wear waterproof gloves throughout the entire preparation procedure. Make all transfers of radioactive solutions with an adequately shielded syringe and maintain adequate shielding around the vial during the useful life of the radioactive product. Do not use if the solution contains particulate matter or is not a clear solution. How Supplied Yttrium-90 Chloride Sterile Solution is supplied as a sterile , non-pyrogenic solution in 2 mL borosilicate vials with teflon-faced chlorobutyl rubber closures. Each vial contains 52 mCi (1924 MBq) of yttrium-90 as of 1200h ET on the intended day of use. Storage Yttrium-90 Chloride Sterile Solution is to be stored at 15-30°C. Expiry
Yttrium-90 Chloride Sterile Solution expires 5 days after the date of calibration. Do not use after the expiry date printed on the package. (11)
Used in formula/calculation: Y-90- A preplan is performed for a yttrium-90 ocular treatment. 1 source is required and 2 were ordered. If the procedure has to be delayed by 1 day, and the same source is to be used, the number of sources now required would be_____. Using the Activity formula of At=Ao e^ -(.693 x time/half-life) the half-life of yttrium-90 is 2.76 days so now insert the given information into the formula. 1x (.693 x 1/2.67) now because it is delayed the e^(.693 x 1/2.67) is not negative. The answer is 1.29 sources will be required.
Uses in Radiation Oncology: Excluding intravascular brachytherapy, the common use of Strontium-90 is in ophthalmic applicators. These applicators are commonly used to treat pterygia and corneal vaculations by direct application of several hundred cGy of radiation to the eye in periods of typically several seconds to one or two minutes, depending on the activity of the applicator.(12) Is used as a temporary implant for treating pterygium, a benign growth of the conjuctiva of the eye.
Sr-90 is employed in ophthalmic surface applicators which typicaly provides 20 -80cGy/sec surface dose.
90 Sr/ 90 Y has also been employed for intravascular brachytherapy applications to inhibit restenosis on coronary lesions (re-closure of the artery after angioplasty). (3). 90Sr/90Y applicators are used in the treatment of skin haemangiomas. Y90- is used as selective internal radi therapy for the treatment of several cancers e.g. hepatic cancer, pancreatic cancer and advance neuroendocrine cancers. (9).
Treatment Planning: The beta particles from Yttrium-90 are ideal for the treatment of superficial lesions of the eye. The dose falls very rapidly away from the applicator and is approximately 20 percent at 2mm-depth in tissue. The dose rate on the surface of such an applicator is in the range of 100 cGy/s; thus each treatment is delivered in seconds. Since the half-life is quite long, stontium 90 applicators are stored and used over many years.(7)
One other interesting fact:
  • Because Sr-90 generates heat as it decays, it is used as a power source for space vehicles, remote weather stations, and navigational beacons. It also is used in industrial gauges and medically, in a controlled manner, to treat bone tumors. (1)
  • Strontium 90 is probably the most-feared fission product. Chemically similar to calcium, it is absorbed along with calcium by the human system and deposited in the bones, where its persistent radioactivity (half-life 28 years) may cause cancer. (2)
  • Stontium was discovered by a Scottish man named Adair Crawford in 1790. It was named after a city in Scotland called Strontianite. Strontium is also used in flares, fireworks and crimson color.
  • Group in Periodic Table: 2 ;Period in Periodic Table: 5;Group Name: Alkaline Earth Metal; Melting Point: 769 degrees Celsius; Boiling Point: 1384 degrees Celsius ;Color when first cut: silvery white; Color after cut: yellowish. (8)
  • It is primarily the 90Y betas that are used for therapy, as the 90Sr betas are mostly absorbed by the stainless steel encapsulation and the surrounding catheter. The 90Sr system (Beta-Cath System) contains sources that are 2.5 mm in length. Source trains of 12 (30 mm), 16 (40 mm) and 24 seeds (60 mm) are commercially available. The sources are stored in a hand-held transfer device and are advanced by a closed loop hydraulic system, which uses sterile water to advance (and then retract) the sources.
  • The advantage of the 90Sr system is the relatively short treatment times (3-5 minutes) and the absence of radiation protection concerns associated with the use of a beta emitter. 90Sr/Y is one of the most energetic beta emitters, which helps reduce the luminal surface dose. The long half-life of the isotope permits the sources to be exchanged on a 6-month basis with no need to change the treatment times during that 6-month period. The disadvantage of this isotope is the potential for attenuation of the betas by calcifications or stents.
  • The Strontium90 vascular brachytherapy system was designed specifically for use in the cath lab and utilizes a patented hydraulic system to deliver the Strontium90 radiation source train into the coronary artery. Strontium90 is an ideal isotope for vascular brachytherapy and the cath lab because it is easy to shield, there is no additional radiation exposure to the cath lab staff and the isotope's 28.8 year half-life means that the treatment times remain consistent from day-to-day use. The multiple radiation source trains (30 mm, 40 mm and 60 mm) allow appropriate radiation coverage of the entire injured area to ensure good clinical outcomes.(10)


Links:
1.Ultrasound guided internal radiotherapy using Y 90: http://jnm.snmjournals.org/cgi/reprint/38/7/1169.pdf
2. Strontium-90 information.http://en.wikipedia.org/wiki/Strontium

References:
1. Centers For disease Control and Prevention. Radioisotope Brief: Strontium-90 (Sr-90). Available at: http://www.bt.cdc.gov/radiation/isotopes/strontium.asp. Accessed on March 19, 2009.

2. Time. Man an Strontium-90. Available at: http://www.time.com/time/magazine/article/0,9171,809133,00.html. Accessed on March 19, 2009.

3. Sources for Temporary Implants. Dosimetry Taining Tool. Available at: www.dosimetrytrainingtool.com. Accessed on March 21, 2009.

4. United States Environmental Protection Agency. Available at www.epa.gov/rpdweb00/radionuclides/strontium.html. Accessed on March 24, 2009.

5. Radioisotopes and Dosimetry in Vascular Brachytherapy. Available at www.content.Karger.com. Accessed on March 24, 2009.

6. Khan, Faiz M. The Physics of Radiation Therapy, Third Edition. Lippincott Williams & Wilkins. 2003. pg. 550.

7. Bentel, Guinilla C. Radiation Therapy Planning, Second Edition. McGraw-Hill. !996. Pg. 534-536.

8. Health Physics society: http://www.hps.org/publicinformation/ate/q429.html

9. Shirish K. Jani, Shirish Jani, K. Handbook of Dosimetery Data of Radiotherapy, illustrated. CRC press1993. pg. 158

10. Strontium-90 brachytherapy uses. Available at:http://www.medscape.com/viewarticle/462111. Accessed on March 25, 2009.

11. Yttrium-90 calibrations. Available at:http://www.mds.nordion.com/documents/products/Package-Insert-Y90-Canada.pdf. Accessed on April 3,2009.

12. VanDyk, Jacob. The Modern Technology of Radiation Oncology. Medical Physics Publishing;1999: pg. 703.

Images: 1. www.radiochemistry.org/.../hanford.htm
2. strontium-90. Available at: www.invasivecardiology.com/article/1917. Accessed 4/8/2009.


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