The investigation of ³²P wire for catheter‐based endovascular irradiation

Abstract

The dose distribution from a 32P source has been measured and calculated in order to evaluate its application in endovascular irradiation. The source dimension was 27 mm in length and 0.3 mm in diameter and was embedded in the end of a Ni-Ti wire. Dose measurements were performed using radiochromic film in several specially designed tissue equivalent phantoms. Loevinger's point dose kernel was used for the calculation. The approximate dose rate at a radial distance of 1.5 mm from the center of the source was found to be 6.75 cGy/s per GBq (0.25 cGy/s per mCi), which allows the delivery of a therapeutic dose in a short time interval with a satisfactory homogeneity without stepping the source. However, the dose rate falls off almost exponentially along the radial distance. Therefore it may not be suitable for treating large diameter vessel from a centrally located source. The effect of a curved 32P wire source on the radial dose distribution was also investigated. The results showed that for a maximum bend of 180 degrees the dose rate was increased by as much as 20% along the inner radial distance but decreased by as much as 20% along the outer radial distance compared to the dose along a straight wire. However, for curvatures normally encountered in a clinical situation, the dose rate was changed less than 5%.

Monte Carlo characterization of a source for intravascular brachytherapy

“…All these are expected to improve the calculation accuracy of angular deflections for electrons, to eliminate restriction on the maximum and minimum electron path length in EGS4/PRESTA-I imposed by the Moliére theory, and to provide an exact boundary-crossing algorithm by using single elastic collisions of electrons. In order to compare with the depth dose curves of Mourtada et al 3 and Xu et al, 2 one-dimensional dose distributions on the transverse axis were also calculated using the EGSnrc code, our modified EGS4 version with user code BRACHD 8,9 and the MCNP code. 4 As mentioned in Sec.…”

“…1 Xu et al carried out an experimental and calculational study for a catheter-based 32 P source wire. 2 More recently, Guidant Vascular Intervention has manufactured a novel catheter-based 32 P IVBT source wire. 3 Mourtada et al 3 have measured depth-dose curves of the source wire in A150 plastic using radiochromic dye film, and in water using an automated plastic scintillator.…”

Improving patient-specific dosimetry for intravascular brachytherapy

“…The DPFs were generated at a radial distance of 2 mm (the prescription point) for a series of circularly curved sources of different bending angles. The data for the 90 Sr and the 192 Ir sources were calculated presently, whereas those for the 32 P were calculated according to the methods described by Xu et al (23).…”

“…Because the curvature factor, F curvature , is introduced to address cold spots, it should be equal to the DPF value in the outward region. The DPF data for the 32 P source were extracted from the work of Xu et al (23) and included for comparison.…”

Endovascular brachytherapy — Treatment planning and radiation protection

“…(The term "dosimetry" is often misused instead of treatment planning.) In endovascular brachytherapy the dose should be measured [2,6,20,30,31,57] as recommended by the AAPM but not only for bctasources. We strongly recommend to calibrate also all endovascular gamma radiation sources by the measurement of the a bsorbed dose (tate).…”