title: The dose distribution produced by a 32P source for endovascular irradiation.
abstract: OBJECTIVE
  Percutaneous transluminal coronary angioplasty (PTCA) is one of the most common therapies for obstructive coronary artery disease. Unfortunately, subsequent restenosis after percutaneous balloon angioplasty occurs in 30-50% of patients and remains one of the major unsolved problems of contemporary cardiology. The study of endovascular irradiation has been greatly stimulated by the discovery that the process of restenosis may be impaired by irradiation. The objective of this study was to examine a custom-made commercial 32P wire and to determine whether the present source presentation is suitable for this application.
  
  
  METHODS
  Measurements of the dose distribution around a 3 mm long 32P source with an activity of 0.414 GBq (11.2 mCi) were made by using LiF thermoluminescent dosimeters and a scintillation detector. The source had the dimensions of 0.3 mm in diameter and 3 mm in length, and was first encapsulated by a plastic tube and then encapsulated in a specially manufactured Ni-Ti wire with a diameter of 0.4 mm and a length of 2.6 m. The detector size effect is removed from the measurements calculation. Loevinger's equation for the dose distribution around a 32P source was used for the calculations.
  
  
  RESULTS
  The dose rate at a radial distance of 1.5 mm was 53 cGy/s per GBq (1.96 cGy/s per mCi) and fell off rapidly perpendicularly to the axis of the source in an approximately exponential manner, from 53-5.3 cGy/s per GBq (approximately 2 to 0.2 cGy/s per mCi) as radial distances increased from 0.2 to 0.4 g/cm2 (1.5 to 3.5 mm away from the center of the source). The treatment length parallel along the wire could be as long as 24 mm for eight source dwell positions with the average dose rate of 59 cGy/s per GBq (2.2 cGy/s per mCi) and a variation of +/- 2.3% at a radial distance of 1.5 mm.
  
  
  CONCLUSIONS
  Our experiments show that the dose distribution is ideal for endovascular irradiation. The source was incorporated in the end of a flexible cable and with a half-life of 14.3 days is suitable for endovascular irradiation.
authors.affiliation: Department of Radiation Oncology, University of Louisville, Brown Cancer Center, KY 40202, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Xu
authors.forename: P R
authors.initials: PR
authors.lastname: Almond
authors.forename: J O
authors.initials: JO
authors.lastname: Deasy
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation*; D004307:Dose-Response Relationship, Radiation; D010761:Phosphorus Radioisotopes / Q000008:administration & dosage*; D011879:Radiotherapy Dosage; D014652:Vascular Diseases / Q000532:radiotherapy
chemical_list: D010761:Phosphorus Radioisotopes