Dosimetry characterization of P-32 catheter-based vascular brachytherapy source wire

Dosimetry measurements and Monte Carlo simulations for a catheter-based P-3 2 endovascular brachytherapy source wire are described. The measured dose r ates were obtained using both radiochromic dye film and an automated plasti c scintillator. The investigated source has dimensions of 27 mm in length a nd 0.24 mm in diameter, and is encapsulated in NiTi. For the radiochromic f ilm measurements, calibrated radiochromic dye film was irradiated at distan ces between 1 and 5 mm from the source axis in A-150 plastic, and read out with a high-resolution scanning densitometer. The depth-dose curve measured in A-150 is then converted to that in water using correction factors obtai ned from Monte Carlo calculations. For the scintillator system, direct meas urements in water were acquired at distances between 1 and 6 mm from the ce nter of the source, along the perpendicular bisector of the source axis. Th e scintillator was calibrated in terms of absorbed-dose rate in a reference beta-particle field at multiple depths. The measured dose rates obtained f rom the film and scintillator measurements were then normalized to the meas ured source activity, i.e., to convert the measured data to units of cGy/s/ mCi. Theoretical dosimetry calculations of the catheter-based P-32 wire geo metry were also obtained from Monte Carlo simulations using the Electron Ga mma Shower code (EGS4), the Monte Carlo N-particle transport code (MCNP4B), and CYLTRAN from the integrated Tiger Series codes (ITS v.3) and found to be in good agreement. The results of both measurements and calculations are expressed as absorbed-dose rate in water per unit of contained activity (c Gy/s/mCi). Comparisons indicate that the measured and calculated dosimetry are in good agreement (<10%) within the relevant treatment distances (1-5 m m). This work fully characterizes the radiation held around a novel P-32 be ta brachytherapy source in water. The depth-dose curve can be used to calcu late the dose to the vessel wall from a 27 mm 32P source wire centered with in the vessel lumen. (C) 2000 American Association of Physicists in Medicin e. [S0094-2405(00)00108-5].