Dosimetry comparison of 192Ir sources

192Ir sources besides being widely utilized in the field of conventional brachytherapy also find use in contemporary peripheral and coronal intravascular applications. In this study, the same Monte Carlo simulation code and input data were used to investigate differences between the dose rate distributions of the most commonly used 192Ir sources in the cm and mm distance range. Findings are discussed in view of differences in source and encapsulation dimensions as well as structural details. Results are presented in the AAPM TG-43 formalism, as generalized by AAPM TG-60, for five 192Ir HDR source designs as well as an LDR seed and an LDR wire source. Dose rate constants of the sources at r0 = 1 cm and r0 = 2 mm were found proportional to the corresponding geometry factors along the transverse source bisectors and an equation of the form lambda r0(cGyh(-1) U(-1)) = 1.12 x G(r0,90 degrees) provides results within clinical accuracy (less than 2%) for any 192Ir source. Radial dose functions do not depend significantly on source and encapsulation geometry and agree within 2% with that of a point 192Ir source. Anisotropy is of importance for accurate dosimetry at the cm distance range but it does not affect dose rate in the mm distance range significantly. At such short radial distances the source geometry factor defines the shape of isodose lines. Dose uniformity at given distances from the sources is strongly dependent on source dimensions as indicated by dose rate profiles in polar and Cartesian coordinates.     

Dosimetry close to an 192Ir HDR source using N-vinylpyrrolidone based polymer gels and magnetic resonance imaging

In this work, the utilization of polymer gel-MRI dosimetry for measurements at distances relevant to clinical brachytherapy and intravascular applications [i.e., in the mm range, where steep three-dimensional (3-D) dose gradients exist] is investigated using N-vinylpyrrolidone-based gels. Transverse axis radial dose distributions, dose distributions parallel to the source axis, and 2-D dose distributions around the commonly used microSelectron 192Ir HDR source are measured for single source dwell position irradiations. Experimental results are found in good agreement with verified Monte Carlo calculations, even for distances less than 3 mm from the source. The effect of various MRI parameters, such as slice thickness, slice mispositioning, and in-plane resolution, on the accuracy of the method is also investigated. Possible limitations of the method are discussed, and its' overall potential in brachytherapy dosimetry is evaluated. Experimental 2-D dose distributions for an intravascular application following the Paris irradiation protocol are compared to corresponding commercial treatment planning system calculations. Results suggest that polymer gel-MRI dosimetry is capable of experimentally verifying dose distributions in relevant clinical intravascular applications.     

Thermoluminescent dosimetry of the selectseed 125I interstitial brachytherapy seed

This work presents experimental dosimetry results for the new selectSeed 125I prostate seed design for use with the seedSelectron afterloading device, in accordance with the AAPM advisory that all new low energy interstitial brachytherapy seeds should undergo one Monte Carlo (MC) and at least one experimental dosimetry characterization. TLD dosimetry was performed using 120 cylindrical LiF TLD type-100 rods calibrated using a 6 MV photon beam. They were irradiated in solid water phantoms for the experimental determination of the seed dose rate constant, radial dose functions and anisotropy functions. MC simulations were performed for the determination of the TLDs relative energy response that was found position independent and equal to 1.40+/-0.03, and for the calculation of the ratio of dose in liquid water to dose in solid water that was found to be well described by Dliquidwater/Dsolidwater= 1.013*r+0.030 presenting only a minor dependence on polar angle. The selectSeed dose rate constant in liquid water was found equal to 0.938+/-0.065 cGy h(-1) U(-1), which agrees within experimental uncertainties with corresponding MC results of lambdaselect Seed=0.954+/-0.005 cGy h(-1) U(-1). The experimental radial dose and anisotropy function results were also found in good agreement with corresponding MC calculations.     

Monte Carlo dosimetry of the selectSeed 125I interstitial brachytherapy seed

This work provides full dosimetric data for the new selectSeed 125I prostate seed source to be distributed by Nucletron B.V. The AAPM TG-43 dosimetric formalism and the new 1999 NIST air kerma strength calibration standard have been followed. Air kerma strength, dose rate constant, radial dose functions, anisotropy functions, and anisotropy factors were calculated using Monte Carlo simulation. Corresponding calculations were also performed for the commercially available 6711 seed source, which is of similar design, for reasons of comparison. The calculated dose rate constant of the selectSeed was 0.954+/-0.005 cGy h(-1) U(-1) compared to 0.953+/-0.005 cGy h(-1) U(-1) for the 6711 source design. The latter value for the 6711 source suggests that the correction factor proposed by NIST for conversion of dose rate constants to the new 1999 NIST calibration standard may be overestimated by 2-3%. Radial dose functions of the two sources were found in good agreement for radial distances up to 4 cm, the selectSeed being less penetrating at greater radial distances (approximately 4% at 10 cm). The selectSeed source presents similar anisotropy characteristics with the 6711 source design. For both source designs, a distance and polar angle dependent discontinuity of anisotropy function values was observed owing to the dose contribution of radioactivity distributed on the ends of the cylindrical source cores. Variation of dosimetric parameters with possible variation in radioactive silver halide coating thickness of the silver source core of the new source was also investigated.     

Endoscopic sphincterotomy in patients with "acalculus" cholangitis associated with juxtapapillary diverticula

BACKGROUND/AIMS: The aim of this study was to investigate patients who underwent endoscopic sphincterotomy for "acalculus" cholangitis associated with juxtapapillary diverticula. METHODOLOGY: In a retrospective study we analyzed 87 patients who underwent endoscopic sphincterotomy for cholangitis; the cholangitis considered "acalculus", when outlining the extra- and intrahepatic bile ducts, we could not observe any intraluminal defect or stricture, and during the clearing of the bile ducts with the balloon, after endoscopic sphincterotomy, there was no evidence of stones, fragments of stones or sludge. Patients who had undergone previous endoscopic sphincterotomy, or who had additional pancreatobiliary diseases were excluded from this study. There were 11 patients with "acalculus" cholangitis associated with juxtapapillary diverticula, and sufficient clinical data available for this study. RESULTS: Nine patients presented pain, fever, and jaundice. In two patients diagnosis was established via the test of abnormal liver biochemistry. Seven patients had positive blood cultures and three of them developed confusion and hypotension. Endoscopic sphincterotomy succeeded in all cases; no evidence of stones, fragments of stones or sludge was recorded during the clearing of bile ducts, after endoscopic sphincterotomy, with the balloon. Five patients presented mild post-endoscopic sphincterotomy complications successfully treated. In the follow-up period, from 4 months to 7 years after endoscopic sphincterotomy, none of the patients developed symptoms of cholangitis. CONCLUSIONS: We recommend endoscopic sphincterotomy in patients with "acalculus" cholangitis associated with juxtapapillary diverticula, despite the absence of obvious obstruction, and the possible morbidity which is inherent with an invasive procedure like endoscopic sphincterotomy.     

Transcatheter occlusion of a large pulmonary arteriovenous malformation with use of a Cardioseal device

Large pulmonary arteriovenous malformations (PAVMs) carry a significant risk of neurologic complications and present technical difficulties in transcatheter treatment with use of coils or detachable balloons. A 26-year-old man with a giant PAVM, who had undergone unsuccessful attempted closure with use of a Gianturco-Grifka occlusion device in the past, underwent successful transcatheter embolization with two Cardioseal double umbrella devices designed for occlusion of intracardiac communications. The procedure was technically easy, had no complications, and provided sustained improvement in arterial saturation and exercise tolerance during follow-up. Transcatheter double umbrella device occlusion of large arteriovenous malformations is feasible and should be considered, especially for very large fistulas.     

Cryoablation of a Nodoventricular Mahaim Fiber

An 11-year old female presented with paroxysmal tachycardia and was diagnosed with a Mahaim fiber during electrophysiologic study. A preexcited tachycardia and the typical variety of AV nodal reentry tachycardia were induced at different times. During preexcited tachycardia, the His bundle electrogram followed the ventricular electrogram, and, introduction of atrial premature beats at different coupling intervals, advanced the peri-AV nodal atrial tissue, with no change in the ventricular cycle length, leading to a diagnosis of an antidromic tachycardia due to a nodoventricular fiber. Cryoablation at a mid-septal location under three-dimensional guidance successfully eliminated both tachycardias without detrimental effects to the AV node.