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| Version | User | Scope of changes |
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| Apr 12 2009, 7:04 PM EDT (current) | olson.lind | 12 words deleted |
| Apr 12 2009, 6:43 PM EDT | olson.lind |
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| Photos: |  Measuring beta radiation from a sample of phosphorus-32. (3) | |
 Galileo™ centering catheter and radioactive phosphorus-32 wire source used in prevention of restenosis. The catheter is inserted in the femoral artery and fed to the coronary artery, where the gold markers can be viewed on an angiogram. The product of the source dose rate and the dwell time in the lesion determines the dose to the arterial wall. (11) |
| Relevant Historical Data: | Phosphorus 32 is an artificially produced isotope that is used for therapeutic purposes. (1) In 2000 Louis Granados filed for a patent for the use of P-32 as a temporary intravascular implant for brachytherapy and as a radioactive stent for balloon angioplasty to help prevent restenosis. (9)(2) |
| Chemical/Radioactive Composition: | Chemical Symbol: P Atomic number (Z, # of protons) = 15 Mass number (A, # of protons + # of neutrons) = 32 Phosphorus-32 is a reactor product and is produced by bombarding Phosphorus-31 with neutrons in a reactor. (4) P-32 is available as a soluble phosphate solution and is generally administered to the patient either intravenously or orally. (4) Typical administered activity of P-32 for bone pain palliation ranges from 5-10 mCi (185-370 MBq). (4) |
| Energy Characteristics: | Phosphorus-32 (P-32) is a pure β-emitter with peak energy of 1.7 MeV and an average energy of 0.694 MeV. (4) P-32 being a β-emitter is best shielded with a low Z material such as plexiglass or acrylic.(4) |
| Exposure Rate Constant: | Since P-32 is a pure beta emitter it has no exposure rate constant. |
| Half-life Properties: | T1/2 14.3 days Decays by beta-minus emission (1) Decays about 5% a day (4) |
| Forms available for use: | Used in the form of sodium phosphate for polycythemia vera, chronic myelocytic leukemia, and chronic lymphocytic leukemia. Used as a tracer in the studies of metabolism of nucleic acids and phospholipids. (5) |
| HVL in lead: | 2mm of water or tissue. Lead is not used as shielding due to the production of Bremsstrahlung x-rays. (6) |
| Measurement/Calibrations/QA: | A comprehensive QA program should assure accurate and safe delivery of intravascular brachytherapy. In addition it should be designed to satisfy the relevant regulations of the NRC or state it is designated as an Agreement State. AAPM G-60 is who the QA reports are most pertinent to involving intravascular brachytherapy. There are certain recommendations of this report such as: document radiation source properties, develop protocols for receipt of sources, acceptance testing, and commissioning procedures are jus a few of them. A comprehensive QA program should assure accurate and safe delivery of intravascular brachytherapy. In addition it should be designed to satisfy the relevant regulations of the NRC or state it is designated as an Agreement State. AAPM G-60 is who the QA reports are most pertinent to involving intravascular brachytherapy. There are certain recommendations of this report such as: document radiation source properties, develop protocols for receipt of sources, acceptance testing, and commissioning procedures are jus a few of them.(7) |
| Used in formula/calculation: | What is the final activity after decay using the information given below? A=A(initial) x e -ln2t/T1/2 ln2=.693 T1/2=14 days t=1 A(initial)= 40.0 mCi A=40.0 mCi x e -.693t/14 days =40.0 mCi x e -.495 =40.0 mCi x .951 =95.1 is the final activity (8) |
| Uses in Radiation Oncology: | Phosphorus-32 is used to treat painful bone metastases for palliation. Typically a 5-10mCi source is used. It is available as a soluble phosphate solution and is generally administered intravenously or orally. Phosphorus is also used to treat polycythemia vera (a disorder characterized by an overproduction of RBCs generally accompanied by an increase in the number of platelets and WBSc), cystic craniopharyngiomas, cystic astrocytomas(8), and chronic myelocytic and chronic lymphocytic leukemias. (5) Phosphorus-32 is also used for intravascular brachytherapy, explained below. (2) |
| Treatment Planning: | The Guidant GALILEO System uses P-32 for intravascular brachytherapy. The source is sealed in the distal tip of a flexible nitinol wire, which can navigate through arteries. This type of system is a remote afterloading device and a treatment planning system is provided to calculate dwell times required to deliver the prescribed dose. (2) Another way P-32 is used for intravascular brachytherapy is in a radioactive liquid form, the Beta-emitting liquid-filled balloon. The advantages of the balloon are inherent source centering and dose uniformity to the vessel wall, the prescription point. The major disadvantages of this technique are higher ratio of surface/adventitial dose compared to the catheter-based gamma source systems and the possibility of balloon rupture, although rare. (2) Permanent stents can also be rendered radioactive with P-32. After balloon angioplasty, as many as half of the patients may experience restenosis. By inserting a radioactive stent with P-32 into the artery, surgery and irradiation are combined into one procedure. (2) P-32 is also used in colloidal form by injection into the serous cavities (pleural and peritoneal) in order to control the malignant accumulation of fluid. (12) |
| One other interesting fact: | Even though the beta particles emitted by P-32 decay have a high amount of energy (1.7MeV), they cannot pass through the layer of dead cells on the skin surface. This means that there is a minimal exposure risk to the radiation unless it is directly applied to the skin or ingested. Most of the risk is eliminated by wearing a lab coat and gloves when working with the isotope. P-32 was also used in the famous Hershey-Chase experiment in 1952 which proved that DNA, not protein, is the carrier of genetic information. (10) |
Links:
Human Radiation Experiments. Available at: http://www.hss.energy.gov/healthsafety/ohre/roadmap/roadmap/index.html
Angioplasty radiation therapy to prevent restenosis. Available at: http://www.freepatentsonline.com/6755776.html
Phosphorus 32. Available at: http://medical-dictionary.thefreedictionary.com/phosphorus-32
Phosphorus 32. Available at: http://dept.kent.edu/ors/ORSContent/ORSBulletins/Rad/SB_P32.pdf
Everything2. Available at: http://everything2.com/title/phosphorus-32
Physics Today on the Web. Available at: Available at: http://www.aip.org/pt/apr00/coursey.html
References:
1. Bentel, Gunilla C. Radiation Therapy Planning. 2nd Edition. McGraw-Hill Companies Inc.; 1996: 537-538. 537
2. Khan, Faiz M. The Physics of Radiation Therapy. 3rd Edition. Philadelphia: Lippincott Williams & Wilkins; 2003: 357-400.
3. United States Department of Energy. Human Radiation Experiments. Retrieved April 1, 2009. Available at http://www.hss.energy.gov/healthsafety/ohre/roadmap/roadmap/index.html
4. Session: 7.7 – Non sealed Radionuclides for Systemic Therapy. Web-Based Dosimetry Training Tool. Retrieved March 16, 2009. Available at:http://www.dosimetrytrainingtool.com
5. The Free Dictionary. Phosphorus 32. Available at: http://medical-dictionary.thefreedictionary.com/phosphorus-32. Accessed March 18, 2009.
6. Phosphorus 32. Available at:http://dept.kent.edu/ors/ORSContent/ORSBulletins/Rad/SB_P32.pdf. Accessed March 17, 2009.
7. Khan, Faiz M. Treatment Planning in Radiation Oncology. 2nd Edition. Philadelphia: Lippincott Williams & Wilkins; 2007: 558-559.
8. Web Based Dosimetry TrainingTool. Radioactive Decay Session 12.04 slide 1. Accessed March 24, 2009. Available at www.dosimetrytrainingtool.com.
9. United States Patents. Angioplasty radiation therapy to prevent restenosis. Retrieved April 1, 2009. Available at: http://www.freepatentsonline.com/6755776.html
10. Everything2. Available at: http://everything2.com/title/phosphorus-32. Accessed April 1, 2009.
11. Physics Today on the Web. Available at: http://www.aip.org/pt/apr00/coursey.html. Accessed April 1, 2009.
12. Lenards, N. D2L Brachytherapy Glossary. Available at: https://uwlax.courses.wisconsin.edu. Accessed April 4, 2009.
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