Catheter-based 32P Wire Source: A Comparison Study of Measured and Calculated Dosimetry in Water

 

F. Mourtada1,2, C. G. Soares1, S. M. Seltzer

1 - S. H. Lott3, R. Colle1 1National Institute of Standards and Technology Gaithersburg, MD 20899

2 - Department of Radiology, School of Medicine, Johns Hopkins University, Baltimore, MD 20874 3 Guidant Corporation, Houston, Texas 77054

Direct dosimetry measurements in water are described for a catheter-based 32P endovascular brachytherapy wire. The measurements were obtained using radiochromic dye film, an automated plastic scintillator. The investigated source has dimensions of 27 mm in length and 0.3-mm in diameter, embedded in the end of Ni-Ti wire. For the radiochromic film measurements, MD55-2 film was irradiated at distances between 1-5 mm in water, and read out with a high-resolution scanning densitometer. For the scintillator system, measurements in water were acquired at distances between 1-6 mm from the center of the source, along the perpendicular bisector of the source axis. The scintillator was calibrated in terms of absorbed-dose rate in a reference beta particle field at multiple depths. Theoretical dosimetry calculations of the catheter-based 32P wire geometry were obtained from Monte Carlo simulations using the Electron Gamma Shower code (EGS4), the Monte Carlo N-Particle transport code (MCNP4B), and CYLTRAN from the Integrated Tiger Series codes (ITS v.3). The results of both measurements and calculations are expressed in absorbed-dose rate per unit of contained activity. Comparisons indicate that the Monte Carlo simulations are in excellent agreement (<3%), but due to source non-uniformity, the plastic scintillator and film dose rates are 20% and 28% lower than the theoretical estimates. This work is underway to develop a novel approach to fully characterize the radiation field around a brachytherapy source in water. The water calibration provides a direct method for producing accurate dosimetry for vascular irradiation at the clinic.