title: Ytterbium-169: a promising new radionuclide for intravascular brachytherapy.
abstract: OBJECTIVE
  To explore the feasibility of 169Yb (gamma, 93 keV) as a new radionuclide for intravascular brachytherapy (IVBT) in terms of dose distribution, penetration power, and radiation safety features as compared with 125I and 192Ir.
  
  
  METHODS
  The dose distributions for catheter-based sources, 169Yb, 125I, and 192Ir, in homogeneous water and in the presence of calcium and a steel stent have been determined and compared using the Monte Carlo method (MCNP4B2 code). The dose rates of the sources were evaluated from 0.02 to 100 cm.
  
  
  RESULTS
  In the short distance range (0.02<r<1.0 cm), the dose distributions in homogeneous water are very similar for the three radionuclides when the dose rates are normalized at 2 mm. Between 1 and 20 cm, the relative dose rates fall off similarly for 169Yb and 192Ir, whereas for 125I, it decreases much more rapidly. At a distance further away (r approximately 100 cm), the dose rate of 169Yb is about 10 times lower than that of 192Ir, indicating the cathlab radiation shielding requirement for 169Yb is substantially reduced as compared with 192Ir. Calcified plaques and stents cause a drastic dose reduction in the arterial wall for 125I, but have no effect for 192Ir gamma-rays. Only slight dose reductions were detected for 169Yb beyond a layer of 1.0-mm calcium (2-3%), and behind a steel stent strut (5%).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiation Oncology, Beth Israel Medical Center and St. Luke's-Roosevelt Hospital Center, 10 Union Square East, New York, NY 10003, USA.
authors.forename: N S
authors.initials: NS
authors.lastname: Patel
authors.forename: P
authors.initials: P
authors.lastname: Fan
authors.forename: S T
authors.initials: ST
authors.lastname: Chiu-Tsao
authors.forename: K
authors.initials: K
authors.lastname: Ravi
authors.forename: W
authors.initials: W
authors.lastname: Sherman
authors.forename: H
authors.initials: H
authors.lastname: Quon
authors.forename: J
authors.initials: J
authors.lastname: Pisch
authors.forename: H S
authors.initials: HS
authors.lastname: Tsao
authors.forename: L B
authors.initials: LB
authors.lastname: Harrison
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D002404:Catheterization; D005240:Feasibility Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000009:adverse effects / Q000493:pharmacokinetics; D007496:Iridium Radioisotopes / Q000009:adverse effects / Q000493:pharmacokinetics; D009010:Monte Carlo Method; D011868:Radioisotopes / Q000009:adverse effects* / Q000493:pharmacokinetics*; D011879:Radiotherapy Dosage; D015018:Ytterbium / Q000009:adverse effects* / Q000493:pharmacokinetics*
chemical_list: D007457:Iodine Radioisotopes; D007496:Iridium Radioisotopes; D011868:Radioisotopes; D015018:Ytterbium