Sign in or 
Share this
Iodine - 125
| Photos: | Figure 1. Iodine-125 Seeds | Figure 2. Interstitial prostate seed implant CT - Iodine-125 |
Fig. 3 Iodine Diagram 6 | Figure 4. I-125 prostate implant |
| Relevant Historical Data: | -Natural abundance is effectively 0%. 1 -Approximately 30 radioactive isotopes of iodine have been made artificially. 6 -In 1946 Allen Reid and Albert Keston discovered Iodine-125, which became important in the field of radioimmunoassay. 13 -Grayish-black non-metallic element, a member of a Halogen group. 9 -Critical organ of I-125 is the thyroid, it is the biological destination. 14 |
| Chemical/Radioactive Composition: | Chemical symbol: I Atomic number (Z): 53 Mass number (A): 125 -I-125 is produced in a nuclear reactor by bombarding Xe-124 with neutrons, which decays via electron capture to I-125. 3 -Electron configuration: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5 4 -Decay of Xe-125 leads to I-125. 7 |
| Energy Characteristics: | -Emits gamma rays with maximum energies of 35.5 keV (7% emitted, 93% internally converted to: 27keV, 31keV, and 27-32 keV some of which are internally converted to x-rays). 1 -Average energy is 28.5 keV. 9 |
| Exposure Rate Constant: | -Exposure rate constant is 1.46 R-cm2/mCi-hr. 2 -The air-kerma strength is 1.27 cGy-cm2/mCi-hr (1.27U). 3 |
| Half-life Properties: | -The half-life of Iodine-125 is 59.4 days. 1,2 -Decays by about 1.2% in one day. 3 -Half-life of Iodine-125 is 60days 15 |
| Forms available for use: | -Commercially available in dilute NaOH solution as [125I]iodide 1 -Seeds 2 -Seed design contains a silver wire that is visible on radiographs, which helps show seed position as well as orientation. 2 -Sources are widely available as seeds or strands for use in interstitial implants 10 -Widely available as seeds with different designs and consists of I-125 sources encapsulated in a titanium shell 10 -To isolate radioiodine capsule is cooled and Xe gas is allowed to escape. 7 |
| HVL in lead: | -0.025 mm Pb 1 -<0.0001 Pb 15 -TVL=.08 mm Pb |
| Measurement/Calibrations/QA: | -Air kerma strength standards are maintained for I-125 seeds. These standards are developed by performing measurements in large volume ion chambers such as the spherical carbon wall ion chamber and the wide angle free air chamber. The calibration of all clinically used brachytherapy sources should be directly traceable to the National Institute of Standards and Technology (NIST) or the Accredited Dosimetry Calibration laboratory (ADCL). 8 -Iodine 125 seeds are calibrated in terms of exposure rate in free space at 1m using a free-air ionization chamber at the NIST. A well-type ionization chamber, whose calibration is maintained by a free-air chamber as the primary standard, is used for routine calibrations. 2 -The process of determining the dose distribution obtained from I-125 seeds is complex and uncertain. However, the development of TLD detectors for dosimetry and computational techniques based on Monte Carlo methods have led to a better understanding of the dosimetry of low energy brachytherapy sources such as I-125 10 |
| Used in formula/calculation: | Mean Life (T avg)= 1.44 T1/2 Mean Life= 1.44 x 59.4 days= 85.5 days Dc= Do x Tavg Dc= 20 cGy/hour x 24 hours/day x 85.5 days= 41,040 cGy 41,040 cGy is the total cumulative dose for a permanent Iodine-125 implant with an initial dose rate of 20 cGy/hour.2 Specific Activity: 1739 Ci/g 16 |
| Uses in Radiation Oncology: | -Prostate cancer and brain tumors 1, ocular melanoma, head and neck cancers (high activity seeds) 3 -Commonly used for temporary brachytherapy applications 3 -Used in studies of the pancreas, blood flow, thyroid, liver, take-up of minerals in bones, and loss of proteins in the body. 6 -Used as an alternative to Iridium-192 for soft tissue sarcoma in pediatric patients. Iodine-125 reduces exposure to caregivers and critical anatomic structures, such as gonads, thyroid, and bony growth plates when compared to Iridium-192. 11 -Used for treating thyroid cancers 12 -Monoclonal antibodies radiolabeled with I-125 have also been used for treatment of high grade gliomas. 12 -Organically bound I-125 solution injected into an inflatable balloon catheter (placed in the tumor cavity) is also being employed for treatment of brain tumors. 12 -Used in permanent low dose radiation brachytherapy. Radioactive pellets filled with iodine are permanently implanted into the prostate cancer patient’s prostate gland. Iodine has a longer half life than palladium-103 which is the other substance used in LDR brachytherapy. Iodine emits lower levels of radioactive energy but gives off energy for longer than the palladium. 14 |
| Treatment Planning: | -Pre-planned or intraoperatively planned 5 -Postplanning can also be done to envision the resultant dose distribution.11 -Planning is much more complex than conventional interstitial sources.2 -The anisotropy (differences in dose distribution around the seed) is higher due to differential attenuation of the low-energy x-ray emissions caused by the seed encapsulation 10 -Planning is done after mapping out the prostate several weeks before the implant procedure with trans rectal ultrasound. A specialized computer program is used to determine the number, strength and placement pattern of the seeds.Typically about 110 seeds are used but the number can vary between 80 -150 seeds. The seeds are inserted using thin each needles. Each needle holds 2 to 6 and the accuracy of the needle placement is monitored directly by transrectal ultrasound and fluoroscopy (x-ray). 17 |
| One other interesting fact: | -Has a neutron capture cross section of 900 barns. During a long irradiation part will be converted to Iodine126. 7 -The Iodine 125 seeds lose 50% of their strength every 2 months and the effective treatment time is about 6 months. By one year from implant their radiation is minimal (<1%). 17 |
Links:
1. Bardurological.com. Iodine-125 seeds. Available at: http://www.bardurological.com/products/loadProduct.aspx?prodID=232. Accessed on March 12, 2009.
2. Nature.com. Iodine seed prostate brachytherapy. Available at: http://www.nature.com/pcan/journal/v7/n3/fig_tab/4500727f2.html. Accessed on March 12, 2009.
3. Iodine-125 Handling Precautions. Available at: http://las.perkinelmer.com/content/TechnicalInfo/TCH_Iodine125.pdf. Accessed April 7, 2009.
References:
1. Wikipedia.com. Iodine-125. Available at: http://en.wikipedia.org/wiki/Iodine-125. Accessed on March 12, 2009.
2. Khan, Faiz M. The Physics of Radiation Therapy. 3rd Edition. Philadelphia: Lippincott Williams & Wilkins; 2003. pp. 358, 367, 545.
3. Module 7, Session 4, pp.29-35. Accessed March 16, 2009, Stanford Web-Based Dosimetry Training Tool. Available at: http://www.dosimetrytrainingtool.com.
4. Radioactive Elements. Available at: http://theodoregray.com/PeriodicTable/Elements/053/data.s7.html. Accessed on March 17, 2009.
5. Medscape Today. Available at: http://www.medscape.com/viewarticle/561945_10. Accessed on March 17, 2009.
6. Iodine. Available at: http://www.chemistryexplained.com/elements/C-K/Iodine.html. Accessed on March 17, 2009.
7. Wikipedia.com Iodine-125. Available at http://en.wikipedia.org/wiki/Iodine-125. Accessed on March 18,2009.
8. Module 7, Session 3, pp3.. Accessed March 18, 2009. Stanford Web-Based Dosimetry Training Tool. Available at: http://www.dosimetrytrainingtool.com.
9. Leibel Steven, Phillips Theodore. Textbook of Radiation Oncology. Philadelphia: W.B. Saunders Company; 1998. p.152.
10. Module 7, Session 4, pp29-33.. Accessed March 19, 2009. Stanford Web-Based Dosimetry Training Tool. Available at: http://www.dosimetrytrainingtool.com.
11. Devlin, Phillip M. Brachytherapy Applications and Techniques. Philadelphia: Lippencott Williams & Wilkins; 2007. pp.45, 283.
12. Module 7, Session 7, pp6. Accessed March 27, 2009. Stanford Web-Based Dosimetry Training Tool. Available at: http://www.dosimetrytrainingtool.com.
13. InteractiveSNM.org. Iodine-125. Available at: http://interactive.snm.org/index.cfm?PageID=1107&RPID=10. Accessed on March 27, 2009.
14. Prostate Cancer Treatment Guide. Iodine-125 in Prostate Cancer Brachytherapy. Available at: http://www.prostate-cancer.com/prostate-cancer-glossary/iodine-125.html. Accessed on April 6, 2009.
15. Ajronline.org. Iodine-125 Source in Interstitial Tumor Therapy. Available at: http://www.ajronline.org/cgi/reprint/123/1/163.pdf. Accessed on April 9, 2009.
16. Khan, Faiz. The Physics of Radition Therapy, 3rd ed. (2003). pp531, 540-2.
17. brachytherapy.co.nz. Prostate Implants New Zealand Ltd. Available at: http://www.brachytherapy.co.nz/brachytherapy.php. Accessed on April 9, 2009.
Color Codes:
Purvi - Orange
Alia - Green
Angie - Blue
Tracey -Red
|
angie garner |
Latest page update: made by angie garner
, Apr 10 2009, 10:53 AM EDT
(about this update
About This Update
Edited by angie garner
8 words added 8 words deleted view changes - complete history) |
|
Keyword tags:
None
More Info: links to this page
|
There are no threads for this page.
Be the first to start a new thread.
