Ytterbium--169


Ytterbium--169 - UW-L Brachy Course

The first image is a picture of the crystallized form of Ytterbium-169 from http://www.webelements.com/webelements/elements/media/xtal-icon/Yb-bs.jpeg
transparent pixel

Ytterbium--169 - UW-L Brachy Course
Ytterbium has a bright, silvery lustre. It is soft, malleable and quite ductile. Here is a picture of it in it's metal form.
http://www.chemsoc.org/viselements/pages/data/graphic/yb_data.jpg

Ytterbium--169 - UW-L Brachy Course
This is the Bohr model of Ytterbium from
http://www.chemicalelements.com/bohr/b0070.gif






Yb-169




Relevant historical data:

Ytterbium was discoveredby the Swiss chemist Jean Charles Galissard de Marignac in 1878. Marignac found a new component in the earth then known as erbia and named it ytterbia (after Ytterby, the Swedish town where he found the new erbia component). He suspected that ytterbia was a compound of a new element he called ytterbium. In 1907, the French chemist Georges Urbain separated Marignac's ytterbia into two components, neoytterbia and lutecia. Neoytterbia would later become known as the element ytterbium and lutecia would later be known as the element lutetium. Auer von Welsbach independently isolated these elements from ytterbia at about the same time but called them aldebaranium and cassiopeium. The chemical and physical properties of ytterbium could not be determined until 1953 when the first nearly pure ytterbium was produced. Ytterbium is one of the more common lanthanides. It is thought to have an abundance of about 2.7 to 8 parts per million in the Earth's crust. That makes it somewhat more common than bromine, uranium, tin, and arsenic. Its most common ore is monazite, which is found in beach sands in Brazil, India, and Florida. Monazite typically contains about 0.03 percent ytterbium.

Chemical/Radioactive Composition:

Chemical Symbol: Yb
Atomic number (Z, # of protons) = 70
Mass number (A, # of protons + neutrons) = 169

Yb-169 is produced in a nuclear reactor by the neutron activation of ytterbium oxide.

Energy Characteristics:

Decay Mode/Types of radiation emitted
Yb-169 decays via electron capture to form Thulium-169 (Tm-169). This transformation yields γ-rays ranging in energy between 60 keV-300 keV with a mean energy of 93 keV.

Exposure Rate Constant:

Dosimetric data
Scarce dosimetry data is available for Yb-169 seed sources but an exposure rate constant (Γ) of 1.8 R-cm2mCi-1hr-1 of has been suggested in the literature.
(Mason et al., "Ytterbium-169: Calculated physical properties of a new radiation source for brachytherapy," Med. Phys. 19, 695-703 (1992))

Half-life Properties:

Half Life (T1/2)
Yb-169 has a half-life of 32 days.
Decay Constant:
Lamda=ln2/32
=0.022

Forms available for use:

Source preparation and encapsulation
Yb-169 is available for brachytherapy application in the form of seed sources similar to the I-125 and Pd-103 seed sources. The Yb-169 seed is about 5 mm in length with an outer diameter of 1 mm in diameter and contains 0.5 mm diameter ytterbium oxide spheres encapsulated in a cylindrical titanium shell.

HVL in lead:

  • Shielding requirements
    Yb-169 has a HVL and TVL in lead of 0.48 mm and 1.6 mm respectively.
  • Yb-169 requires less shielding as compared to Cs-137 and Ir-192 e.g. the HVL in lead for Yb-169 is only 0.48 mm as compared to an HVL in lead of 6.5 mm and 6 mm for Cs-137 and Ir-192 respectively.


  • Measurement/Calibrations/QA:

    Analytic and Monte Carlo computations have been used to predict physical quantities useful in treatment planning and radiation protection. Analytic calculations based on the primary photon spectrum of 169Yb (excluding energies less than 10 keV) yield an air-kerma rate constant of 0.0427 cGy cm2 h-1 MBq-1, and an exposure rate constant of 1.80 R cm2 mCi-1 h-1 for this radionuclide. Calculated fmed factors are 0.922 cGy/R for soft tissue and 2.12 cGy/R for bone.

    Used in formula/calculation:

    Tavg=1.44 x (32 days) =46.08 days
    Dc=Do x Tavg
    Dc= 300 mCi x (46.08 days) = 13824 mCi
    This is the total dose accumulated (Dc) if Ytterbium169 was used in a permanent implant treatment plan with an original dose of 300mCi.

    Uses in Radiation Oncology:

    Clinical Use
    Yb-169 is used as a substitute for Ir-192 and Cs-137 for temporary implants
    Advantages
    • Yb-169 has a high specific activity and hence small sources can be designed for interstitial and intracavitary implants.
    • Yb-169 provides a higher initial dose rate for permanent implants compared to I-125.

    Treatment Planning:

    Brachytherapy afterloaders are currently being developed that offer effective low-energy HDR cancer treatments while minimizing the need for shielding. Such devices will make use of ytterbium-169, a low-energy isotope with a mean energy of 93 keV (compared with 370 keV for iridium-192, the isotope most commonly used in existing HDR afterloaders).
    Such a system enables clinicians to offer better treatment options in cases where implantation of treatment applicators takes place somewhere other than the treatment room. This applies in the main to accelerated partial-breast brachytherapy, but could also be relevant to procedures such as gynaecological, sarcomas, prostate, oesophagus, endobronchial and all intraoperative treatments where movement to a full-shielded facility is undesirable or, in some cases, not possible. In all of these cases, the primary procedure is often not performed in the radiation oncology department, such that it may be more convenient for all concerned for the treatment device to travel to the patient rather than the other way round.

    One other interesting fact:

    It is named for Ytterby, a town in Sweden

    169Yb is a promising new radionuclide for IVBT. It has a much better penetrating power through calcified plaques and stents compared with the low-energy source 125I. It also provides easier radiation protection measures for cardiac cathlab personnel than the high-energy source 192Ir, while preserving a favorable dose distribution in tissues surrounding an arterial vessel.

    mean gamma emission 93 keV, after excluding photons of energy less than 10 keV

    Disadvantages

    • Higher γ- ray energies increase the cost of shielding.



    Links:
    http://bjr.birjournals.org/cgi/content/abstract/65/771/252

    http://www.ncbi.nlm.nih.gov/pubmed/1508110

    http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRN-44V0R66-9&_user=4677475&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000063905&_version=1&_urlVersion=0&_userid=4677475&md5=7f3770840ca9eadab11e285349108de6

    http://www.reference.com/search?q=ytterbium

    http://www.dosimetrytrainingtool.com/
    http://medicalphysicsweb.org/cws/article/opinion/25383

    References:
    "Ytterbium-169". http://www.dosimetrytrainingtool.com/

    "The potential of ytterbium 169 in brachytherapy: a brief physical and radiobiological assessment."
    The British Journal of Radiology, Vol 65, Issue 771 252-257, Copyright © 1992 by British Institute of Radiology

    "Ytterbium-169: calculated physical properties of a new radiation source for brachytherapy"Mason DL, Battista JJ, Barnett RB, Porter AT.Department of Medical Biophysics, University of Western Ontario, London, Canada. Med Phys. 1992 May-Jun;19(3):695-703.


    Ytterbium-169: A promising new radionuclide for intravascular brachytherapy
    Neil S. Patel. Department of Radiation Oncology, Beth Israel Medical Center and St. Luke's-Roosevelt Hospital Center, 10 Union Square East, New York, NY 10003, USA
    Sun Microsystems, Hackensack, NJ, USA
    Received 21 June 2000; revised 2 April 2001; accepted 25 May 2001. Available online 3 January 2002.

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