MEASUREMENTS OF SPATIAL CORRELATIONS OF IONISATION CLUSTERS IN THE TRACK OF CARBON IONS-FIRST RESULTS.

An attempt towards an experimental set up which could provide the experimental data on correlation processes occurred simultaneously in two distanced DNA targets within a charged particle track is presented. A modified Jet Counter nanodosemeter was used in two experiments with carbon ions with mean energies of 52 and 23 MeV. The probability distributions of the correlated pairs of ionisation clusters produced in two neighbouring sensitive volumes are presented. A question of potential new descriptors of radiation quality is raised.

Status report: Nanodosimetry of carbon ion beam at HIL.

We present preliminary data for measured distributions of ionization cluster size produced by carbon ions in tissue equivalent media. The experiments were carried out with a beam of 92 MeV carbon ions from the U200p cyclotron at the Heavy Ion Laboratory (HIL), University of Warsaw, and nitrogen targets using the so-called Jet Counter set-up.

Nanodosimetry of (125)I Auger electrons.

PURPOSE: The nanodosimetric description of the radiation action of Auger electrons on nitrogen targets of nanometric size is presented. MATERIALS AND METHODS: Experimental microdosimetry at nanometer scale for Auger electrons has been accomplished with the set-up called Jet Counter. This consists of a pulse-operated valve which injects an expanding nitrogen jet into an interaction chamber where a gaseous sensitive volume of cylindrical shape is created. The ionization cluster size distributions (ICSD) created by Auger electrons emitted by (125)I while crossing a nanometer-sized volume have been measured. RESULTS: The ICSD for the sensitive volumes corresponding to 3 and 12 nm in diameter (in unit density 1 g/cm(3)) irradiated by electrons emitted by a (125)I source were collected and compared with the corresponding Monte Carlo (MC) simulation. The preliminary results of the experiments with Auger electrons of (125)I interacting with a nitrogen jet having nanometric size comparable to a deoxyribonucleic acid (DNA) and nucleosome, showing the discrete spectrum of ICSD with extended cluster size, are described. CONCLUSIONS: The presented paper describes for the first time the nanodosimetric experiments with Auger electrons emitted by (125)I. A set of the new descriptors of the radiation quality describing the radiation effect at nanometer level is proposed. The ICSD were determined for the first time for an Auger emitter of (125)I.

Enhanced level of micronuclei in peripheral blood lymphocytes of patients treated for restenosis with 32P endovascular brachytherapy.

BACKGROUND: Restenosis is the complete occlusion of the blood vessel leading to such complications as ischemia/angina, myocardial infarction, and death. It can be managed by endovascular brachytherapy with both gamma and beta sources. Endovascular brachytherapy is performed worldwide on several thousands of cases per year. The gamma-emitter 192Ir as well as the beta-emitters 32P and 90Sr are mainly used. The dose to the occluded endothelial wall is 20 Gy. Interestingly, no information with respect to the dose absorbed by the blood during the course of the treatment exists. The aim of the present investigation was to verify if the micronucleus test is suitable to detect the dose absorbed by lymphocytes in the course of endovascular brachytherapy with 32P. MATERIALS AND METHODS: Blood was drawn from 16 patients immediately before and 1 day after the treatment. Frequencies of micronuclei were assessed. In order to ensure that the micronuclei did not arise due to fluoroscopy or reperfusion, we analyzed lymphocytes of 16 control patients who underwent interventional cardiology with balloon angioplasty only. RESULTS AND CONCLUSIONS: Enhanced frequencies of micronuclei were observed in lymphocytes of some donors following brachytherapy. No correlation could be detected between the level of induced micronuclei and the absorbed dose. Also, no effect of fluoroscopy or reperfusion was seen. Thus, although brachytherapy of restenosis with 32P leads to weak enhancement of the micronucleus frequency in lymphocytes, the effect was not seen in all patients; the reason for this heterogeneous response remains to be elucidated.

Acute lumen overdilation improves outcome after brachytherapy of in-stent restenosis.

BACKGROUND: The aim of our study was to test the impact of acute lumen overdilation on neointimal hyperplasia and late lumen size after vascular brachytherapy for in-stent restenosis (ISR). METHODS: Forty-seven ISR lesions located in 47 coronary arteries in 44 consecutive patients underwent beta brachytherapy with serial intravascular ultrasound studies. Vessel, lumen, and stent cross-sectional area were measured at 1-mm steps. Based on an interpolated reference cross-sectional area, each cross section was assessed as overdilated (lumen cross-sectional area>interpolated reference cross-sectional area) or not overdilated (lumen cross-sectional area

Effectiveness and determinants of the long-term beta intracoronary brachytherapy results.

BACKGROUND: Effectiveness evaluation and search for the factors determining long-term results of beta intracoronary brachytherapy (ICBT) are of a special importance in an upcoming era of drug-eluting stents usage for a wide range of clinical indications: de novo and in-stent restenosis lesions. METHODS: One hundred forty eight consecutive patients (59.6+/-9.6 years, 72% men) treated with beta ICBT for in-stent restenosis (ISR) or de novo lesions were studied. There were 135 ISR in 121 patients and 31 de novo lesions in 27 patients. Follow-up coronary angiography was performed in all patients after a mean of 8.9+/-4.5 months. Detailed qualitative and quantitative angiographic analysis of pre-, peri- and postprocedural as well as follow-up angiograms was performed. RESULTS: Forty five percent of patients treated for de novo lesions were diabetic. Thirty five percent of all targets were located in vessels with a reference vessel diameter <2.5 mm. Furthermore, 77% of ISR lesions were in Class 1 according to the Mehran classification. The mean length of an irradiated segment was 37.6 mm. The overall recurrent restenosis rate was 28.3%. Multivariate analysis revealed that the reference vessel diameter and the presence of edge injury within the proximal 32P source dose-fall off were the only independent predictors of recurrent restenosis after ICBT (OR 0.46; 95%CI 0.24-0.89; p=0.021 and OR 2.55; 95%CI 1.23-5.25; p=0.011, respectively). CONCLUSIONS: Recurrent restenosis after beta intracoronary brachytherapy treatment is negatively associated with the target vessel size. Presence of edge injury within the proximal 32P source dose-fall increases the frequency of recurrent renarrowing after ICBT. Our results indicate that target vessel size should be taken into account in optimising interventional strategy for ISR treatment: drug eluting stents versus intracoronary brachytherapy. Avoidance of edge injury within the proximal 32P source dose fall-off is strongly recommended while ICBT application.

Angiographic restenosis following intravascular beta-brachytherapy does not correlate with delivered dose: a study with dose volume histograms. Recurrence of in-stent restenosis after brachytherapy.

INTRODUCTION: Vascular brachytherapy reduces recurrence after treatment of in-stent restenosis. However, there are still failures. The aims of the study were to investigate the relationship between two distinct dose prescriptions and the calculated dose delivered versus binary angiographic restenosis. METHODS AND MATERIALS: Fifty-five lesions in 47 patients underwent catheter-based beta-brachytherapy with a (32)P source. Doses delivered were calculated using intravascular ultrasound (IVUS) measurements. Patients randomly received 20 Gy either at 1 mm beyond mean reference lumen or 1 mm beyond mean reference external elastic membrane. Using subsequent off-line volumetric IVUS measurements, dose volume histograms (DVHs) for the adventitia were determined. RESULTS: There were 13 restenotic lesions including four total occlusions. All recurrences localized within stented segment. The frequency of restenosis was similar between dosimetry groups (20% vs. 28%; P=.5). DVH calculations were similar in restenotic versus restenosis-free lesions. However, postprocedural IVUS minimal lumen area was significantly smaller for lesions that recurred (5.03+/-1.19 mm(2) vs. 6.13+/-1.7 mm(2); P=.042). CONCLUSIONS: Calculated cumulative doses delivered to the tissues do not correlate with clinical outcome. However, an adequate lumen may be important to accommodate even a small amount of recurrent intimal hyperplasia to limit restenosis and need for target lesion revascularization.

The "shielding" effect of the guide wire during coronary brachytherapy with P-32 source.

Intracoronary beta irradiation (use of beta radiation for intracoronary irradiation) is an effective method in reducing neointimal proliferation after successful angioplasty and stent implantation. However, long-term results may be influenced by absolute dose and by the homogeneity in dose distribution. In our study, we investigated dose perturbation due to the presence of a conventional guide wire during irradiation. The Galileo III centering catheter and P-32 beta source were used. The 55 MD GAF Chromic foil was positioned within a phantom made of PMMA. The dose distribution at cylindrical surfaces has been assessed using GAF Chromic dosimetric foil MD55 (Nuclear Associates, USA). Our study demonstrated the significant dose reduction of 46% in the most "shaded" area. The dose reduction to 80% or less occupy the 60 degrees sector. This phenomenon can cause progression of late restenosis. In conclusion, the results suggest that technical improvements in centering catheter construction should be made to eliminate the "shielding" effect of the guide wire.