phosphorus-radioisotopes and Calcinosis

Accurate patient-specific dosimetry in intravascular brachytherapy (IVBT) is generally difficult due to the extremely high-dose gradient, complexity of treatment device, and patient-specific geometry (e.g., calcification, stent, curvature, movement of target). The purpose of this study is to analyze quantitatively and systematically the dose effects of calcification, stent, guidewire, and source curvature on clinical dosimetry in an IVBT procedure, and propose a method that can be used to assess these effects in routine clinical practice.. Monte Carlo techniques were used to calculate 3-D dose distribution in both homogeneous and inhomogeneous media for three most commonly used IVBT sources: (90)Sr beta (Novoste), (192)Ir gamma (Cordis/Best), and (32)P beta (Guidant). Dosimetric perturbations in the presence of metallic stents, calcified plaques, metallic guide wires, and source curvature were studied for situations commonly encountered in the clinic. The importance of each of these perturbations and their practical influence on patient-specific dosimetry were analyzed. Factors (plaque, stent, guidewire, and curvature) that may be used to correct/reduce these perturbations were introduced to prevent dosimetric cold spots during IVBT. Practical methods of using these correction factors are proposed.. Dose perturbations are significant due to the presence of source curvature, metallic stents, calcified plaques, and metallic guide wires, especially for beta sources. These perturbations can be as high as 30% under normal clinical conditions, although they can be much higher in extreme situations. Empirical relationships of plaque factor with the thickness of calcified plaque, stent factor with stent metallic surface area, guidewire with guidewire thickness, and curvature factor with the bending angle are derived. These relationships are found to be useful in improving clinical dose accuracy in IVBT treatment planning or dose evaluation after treatment.. Significant dose perturbations due to the presence of source curvature, metallic stents, calcified plaques, and guide wires have been found in IVBT for in-stent restenosis. Because it has been reported that, with the current prescriptions for IVBT, higher doses consistently improve treatment outcomes, the empirical method derived from this work can be used to assess cold spots dosimetrically, thus improving patient-specific dosimetry for IVBT.

Topics: Blood Vessel Prosthesis Implantation; Brachytherapy; Calcinosis; Combined Modality Therapy; Coronary Restenosis; Dose Fractionation, Radiation; Equipment Design; Humans; Iridium Radioisotopes; Monte Carlo Method; Phosphorus Radioisotopes; Radiotherapy Planning, Computer-Assisted; Stents; Strontium Radioisotopes

A new Monte Carlo code (IVBTMC) is developed for accurate dose calculations in intravascular brachytherapy (IVBT). IVBTMC calculates the dose distribution of a brachytherapy source with arbitrary size and curvature in a general three-dimensional heterogeneous medium. Both beta and gamma sources are considered. IVBTMC is based on a modified version of the EGSNRC code. A voxel-based geometry is used to describe the target medium incorporating heterogeneities with arbitrary composition and shape. The source term is modeled using appropriate phase-space data. The phase-space data are calculated for three widely used sources (32P, 90Sr/90Y, and 192Ir). To speed up dose calculations for gamma sources, a special version of IVBTMC based on the kerma approximation is developed. The accuracy of the phase-space data model is verified and IVBTMC is validated against other Monte Carlo codes and against reported measurements using radio-chromic films. To illustrate the IVBTMC capabilities, a variety of examples are treated. 32P, 90Sr/90Y, and 192Ir sources with different lengths and degrees of curvature are considered. Calcified plaques with regular and irregular shapes are modeled. The dose distributions are calculated with a spatial resolution ranging between 0.1 and 0.5 mm. They are presented in terms of isodose contour plots. The dosimetric effects of the source curvature and/or the presence of calcified plaques are discussed. In conclusion, IVBTMC has the capability to perform high-precision IVBT dose calculations taking into account the realistic configurations of both the source and the target medium.

Topics: Brachytherapy; Calcinosis; Computer Simulation; Humans; Iridium Radioisotopes; Monte Carlo Method; Phosphorus Radioisotopes; Radiometry; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Sensitivity and Specificity; Software; Strontium Radioisotopes; Vascular Diseases; Yttrium Radioisotopes

Topics: Acute Pain; Calcinosis; Disease; Humans; Periarthritis; Phosphorus; Phosphorus Radioisotopes; Wrist; Wrist Joint