strontium-radioisotopes and Vascular-Diseases

The aim of this study was to investigate if microMOSFETs are suitable for the dosimetry and quality assurance of beta sources. The microMOSFET dosimeters have been tested for their angular dependence in a 6 MeV electron beam. The dose rate dependence was measured with an iridium-192 afterloading source. By varying the source-to-surface distance (SSD) in a 12 MeV electron beam the dose rate dependence in an electron beam was also investigated. To measure a depth dose curve the dose rate at 2, 5, 8 and 12 mm distance from the beta source train axis was determined with the OPTIDOS and the microMOSFET detector. A comparison between the two detector types shows that the microMOSFET is suitable for quality assurance of beta sources for endovascular brachytherapy (EVBT). The homogeneity of the source is checked by measurements at five points (for the 60 mm source at 10, 20, 30, 40 and 50 mm) along the source train. The microMOSFET was then used to evaluate the influence of a common stent type (single layer stainless steel) on the dose distribution in water. The stent led to a dose inhomogeneity of +/-8.5%. Additionally the percentage depth dose curves with and without a stent were compared. The depth dose curves show good agreement which means that the stent does not change the beta spectrum significantly.

Topics: Biophysical Phenomena; Biophysics; Brachytherapy; Gamma Rays; Humans; Quality Assurance, Health Care; Radiometry; Radiotherapy Planning, Computer-Assisted; Radiotherapy, High-Energy; Stents; Strontium Radioisotopes; Vascular Diseases; Yttrium Radioisotopes

Beta emitting source wires or seeds have been adopted in clinical practice of intravascular brachytherapy for coronary vessels. Due to the limitation of penetration depth, this type of source is normally not applicable to treat vessels with large diameter, e.g., peripheral vessel. In the effort to extend application of its beta source for peripheral vessels, Novoste has recently developed a new catheter-based system, the Corona 90Sr/90Y system. It is a source train of 6 cm length and is jacketed by a balloon. The existence of the balloon increases the penetration of the beta particles and maintains the source within a location away from the vessel wall. Using the EGSnrc Monte Carlo system, we have calculated the two-dimensional (2-D) dose rate distribution of the Corona system in water for a balloon diameter of 5 mm. The dose rates on the transverse axis obtained in this study are in good agreement with calibration results of the National Institute of Standards and Technology for the same system for balloon diameters of 5 and 8 mm. Features of the 2-D dose field were studied in detail. The dose parameters based on AAPM TG-60 protocol were derived. For a balloon diameter of 5 mm, the dose rate at the reference point (defined as r0 = 4.5 mm, 2 mm from the balloon surface) is found to be 0.01028 Gy min(-1) mCi(-1). A new formalism for a better characterization of this long source is presented. Calculations were also performed for other balloon diameters. The dosimetry for this source is compared with a 192Ir source, commonly used for peripheral arteries. In conclusion, we have performed a detailed dosimetric characterization for a new beta source for peripheral vessels. Our study shows that, from dosimetric point of view, the Corona system can be used for the treatment of an artery with a large diameter, e.g., peripheral vessel.

Topics: Brachytherapy; Catheters, Indwelling; Humans; Iridium Radioisotopes; Monte Carlo Method; Radiometry; Radiopharmaceuticals; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Sensitivity and Specificity; Strontium Radioisotopes; Vascular Diseases; Water; Yttrium 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

A quality assurance system (OPTIDOS, PTW-Freiburg) developed for dose rate verification of 90Sr/90Y radiation source trains (RSTs) was calibrated and validated. These source trains are used in the 5-F-BetaCath system (Novoste Corp.) for the treatment of endovascular diseases. The calibration factor of the OPTIDOS system was obtained empirically and is valid for 90Sr/90Y dose rate measurements at the specification point which is located at 2 mm distance from the source axis. A total of 187 OPTIDOS dose rate verifications of the 5-F-BetaCath system were performed in different hospitals. The histogram of the deviation between the manufacturer's dose rate specification and the dose rate measured using the OPTIDOS dosimetry system is Gaussian shaped with +/- 3% relative width and a mean shift of about +2% with respect to the corresponding dose rate specification. Additionally, 128 OPTIDOS dose rate verifications of the new jacketed RST (3.5-F-BetaCath, Novoste Corp.) were performed using the same calibration factor as derived for the 5-F-BetaCath system. Distribution of the deviation between the certified and the measured dose rate is nearly identical in comparison to the histogram of the 5-F-BetaCath system. The mean value of the deviations is shifted by -1.5% with respect to the certified dose rate. In order to compare the results of the calibrated OPTIDOS dosimetry system with a standard measuring method, separate dose rate measurements were performed using electron accelerator calibrated radiochromic films in which calibration is traceable to PTB (Physikalisch Technische Bundesanstalt, Germany). Deviation between both the methods is less than 3.1%. These results confirm that the calibrated OPTIDOS dosimetry system can be considered suitable for quality assurance of both types of RST used in the BetaCath systems.

Topics: Beta Particles; Brachytherapy; Calibration; Equipment Design; Film Dosimetry; Humans; Quality Assurance, Health Care; Radiometry; Radiotherapy Dosage; Reproducibility of Results; Sensitivity and Specificity; Strontium Radioisotopes; Vascular Diseases; Yttrium Radioisotopes

Coronary artery brachytherapy may require treatment of lesions longer than a single source length. A treatment option is tandem positioning of the single source. This study presents relative dosimetric measurements of a cardiovascular brachytherapy source and the dosimetric characteristics in the junction region of tandem treatments. Measurements were carried out using a Novoste Beta Cath 90Sr/90Y 40 mm beta source in a plastic water phantom. Radiochromic MD-55-2 film, calibrated using both 6 MV photon and 6 MeV electron beams from a linear accelerator, was used as the dosimeter. Dose distributions around a single source and in the junction region of tandem irradiation were measured. Measurements of the near field dose as close as 1.2 mm from the source are presented. Significant over- or underdoses in the junction region of tandem irradiation were quantified. At a radial distance of 2 mm from the longitudinal axis of the source, the dose value in the middle of the junction region, normalized to the dose at 2 mm midline single source, was about 182% for a 2-seed overlap and 16% for a 2-seed gap, respectively. Dose distributions in the junction region as a function of source overlap and radial distance have fairly high gradients and exhibit characteristic patterns. The fraction of prescription dose was found to have a sigmoidal dependence on overlap size, for radial distances ranging between 1.2 and 3 mm. The parameters of these sigmoids, quantified as functions of radial distance, could be used to provide quick and reasonable over/underdose estimates, given any potential overlap or gap in the junction area, with an uncertainty within 10%.

Topics: Beta Particles; Brachytherapy; Coronary Restenosis; Film Dosimetry; Humans; Piperazines; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Computer-Assisted; Reproducibility of Results; Sensitivity and Specificity; Strontium Radioisotopes; Vascular Diseases; Yttrium Radioisotopes