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PubMedDate not supplied

Absolute radioactivity measurements by the use of a 4pibeta-4pigamma detector configuration.

The radioactivity of 60Co and 134Cs sources were measured using a 4pibeta-4pigamma detector configuration with a well-type NaI(Tl) crystal and a sandwich type 4pibeta detector composed of two sheets of NE102A plastic scintillator coupled to a slender photomultiplier tube. The beta-detector was inserted into the well of the gamma-detector. Since counting efficiencies in both the beta- and gamma-channels can be kept high, excellent counting statistics were attainable even when weak sources were measured. This configuration can also be used for radioactivity measurements based upon the direct integral counting of 4pibeta + 4pigamma logic sum signals, and two independent results can be obtained for every measurement. This technique is especially useful for the standardization of complex decaying nuclides.

Beta Particles↗
PubMedDate not supplied

Application of pulse mixing method in software coincidence counting.

In recent years the software coincidence counting system, designed for absolute activity measurement, has been developed in the Czech Metrology Institute. In this system a true coincidence count rate is calculated from the records of time and amplitude data of individual pulses and may be determined by two different methods. The first one uses a coincidence resolving time, in a manner similar to a classical coincidence measurement. The second method applies the pulse mixing method formulae, so that it does not use the resolving time and the correction for accidental coincidences. Both methods have been tested on the same data from a 4pibeta (PC)-gamma coincidence measurement of 60Co sources. The difference between the results obtained from both calculation methods applied on the data from the same measurement did not exceed 0.015%. The details of both methods and the results of their comparison are presented.

Algorithms↗
PubMedDate not supplied

Construction and implementation of the NIST triple-to-double coincidence ratio (TDCR) spectrometer.

A description of the triple-to-double coincidence ratio (TDCR) spectrometer recently constructed at NIST and results of tests to assess its operating characteristics are presented. Measured activities for previously calibrated solutions of 3H (tritiated water) and 63Ni agreed with certified activity values to within 0.04% and 0.2%, respectively. Agreement between measurements of solutions containing 90Y using the TDCR and the CIEMAT/NIST efficiency tracing method was achieved to within 0.7% and within the respective experimental uncertainties. A difference of 5.3% was observed between TDCR measurements and the certified massic activity value for a calibrated solution containing 54Mn, but because of the large uncertainty on the TDCR result (3.6% relative standard uncertainty), the values agree to within the experimental uncertainties. Agreement to within experimental uncertainties (2%) for 103Pd was achieved with the TDCR and CIEMAT/NIST methods, but not between TDCR and isothermal calorimetric measurements. TDCR results for a 204Tl solution were in excellent agreement (maximum difference of 0.2% with any other method, with combined standard uncertainty of 0.45% on TDCR result) with results obtained using three other methods.

Beta Particles↗
PubMedDate not supplied

Measurement of a 103Pd solution using the TDCR method by LSC.

Palladium 103 is a radionuclide used in brachytherapy sources for the treatment of prostate cancers and also for other medical applications. It decays through electron capture to excited levels of 103Rh. This paper describes the calculation method used to compute the detection efficiency in the framework of the triple to double coincidence ratio model. The calculation of the energy transferred to the scintillator is made by considering the various atomic events following the electron capture and the electron conversion. The energy deposited in the scintillator after the absorption of X-rays is calculated using the PENELOPE stochastic calculation code. The main contributors to the final uncertainty and their covariance matrix are discussed. As the calculation method cannot be reduced to an explicit function, this paper describes the Monte Carlo method used for the evaluation of uncertainties.

Algorithms↗
PubMedDate not supplied

Transfer standard for beta decay radionuclides in radiotherapy.

The measurement of the activity of therapeutic radiopharmaceuticals prior to the administration to patients is normally achieved via the use of radionuclide calibrators. An accurate measurement of the activity of pure beta-emitters is complex. Calibration problems can be solved by combining a primary calibration with a 90Y reference solution and a 90Sr/90Y transfer standard with a solid source, simulating geometric effects caused by high energetic beta radiation. The recent development of a 90Sr/90Y transfer standard for this purpose is reported.

Beta Particles↗
PubMedDate not supplied

Standardization of a 32P solution containing pure-beta impurities using the TDCR method in liquid scintillation counting.

The liquid scintillation counting standardization of pure-beta solutions containing pure-beta emitter impurities is a difficult task because, unlike that which can be achieved by using gamma-ray spectrometry, the continuous characteristics of beta spectra and the poor intrinsic resolution of LSC spectrometers do not allow an easy identification and precise determination of the activity concentration of these impurities. This problem was recently encountered in the standardization of a 32P solution in the framework of an international comparison, where the activity contribution of the impurities was over 10% of the main nuclide activity at the reference date. This paper describes the method used to identify the impurities in this 32P solution and the calculation of the detection efficiencies using the triple to double coincidence ratio model. Details on the calculation of the uncertainties of each activity and the covariances between these activities are given.

Algorithms↗
PubMed2006

Activity measurements of the high-energy pure beta-emitters 89Sr and 90Y by the TDCR efficiency calculation technique.

The absolute activities of the pure beta-emitters 89Sr and 90Y have been determined by a direct method, namely the triple-to-double coincidence ratio (TDCR) efficiency calculation technique. This undertaking has extended further the number of radionuclides that have been standardized by this non-extrapolation liquid scintillation (LS) method. Both measurements were carried out within the framework of international key comparisons under the auspices of the International Bureau of Weights and Measures (BIPM). The TDCR results agreed well with those of other participating national laboratories, most using alternative (tracer) methods.

Algorithms↗
PubMed2006

Standardization of radionuclide by beta(LS)-gamma coincidence counting using the geometry-efficiency variation method.

A liquid scintillation counting method consisting of three photomultiplier tubes for beta counters and a NaI(Tl) gamma counter has been developed for the standardization of radionuclides with the beta-gamma coincidence technique. The beta detection efficiency functions are obtained by means of a geometry-variation method developed in the present work; an array of beta detectors is moved uniformly at the same time from a centrally located counting vial to 50 mm. The method has been applied in the standardization of 60Co and 134Cs. Unquenched liquid scintillation samples with nominal count rates from 1000 to 6000 s-1 were prepared. The observed beta detection efficiencies with this method are from 90 to 45% in the case of 60Co, and from 84 to 50% for 134Cs. The output of each beta channel is summed together and compared with gamma data by the coincidence analyzer. The dead time of each counting channel is adjusted to be 20 micros, sufficiently long to suppress the afterpulses in the beta counting channel. The activity of each sample is determined by using the Cox and Isham formula. The obtained results are in good agreement with KRISS certified values.

Beta Particles↗
PubMed2006

Theoretical data of external Bremsstrahlung radiation cross-section of bone.

Theoretical data of external Bremsstrahlung (EB) radiation cross section of bone is estimated using tabulated results of EB cross section given for various elements at various photon and electron energies. This data may be useful in the analysis of Bremsstrahlung imaging which is the technique applied in medical therapy.

Beta Particles↗
PubMedDate not supplied

Prevention of intimal hyperplasia; Initial results with low-dose beta-radiation applied by an external vascular polymer wrap.

OBJECTIVE: Endovascular brachytherapy, delivered by a variety of catheter-based devices, has proven clinically effective for the inhibition of neointimal hyperplasia (NIH) after coronary and peripheral balloon/stent angioplasty. No platform, however, has been developed to deliver low-dose radiation in concert with vascular surgical operations. The purpose of this study was to evaluate the vascular response following balloon injury to the rabbit carotid artery, with and without topical low-dose 45Ca, applied by an external vascular "wrap". METHODS: Twelve rabbit carotid arteries were subjected to balloon injury by embolectomy catheter. The common carotid artery was then "wrapped" circumferentially with a biostable polyurethane membrane (Nanoskin Secant Medical, Perkasie, PA), without radiation (n = 6), or with radiation (n = 6) (45Ca approximately 50 microCi). The animals were sacrificed at 4 weeks for histologic assessment of the treated vessels. RESULTS: The 45Ca wrap inhibited NIH evidenced by trends towards reduction of intimal area (0.46 +/- 0.19 control carotid vs. 0.35 +/- 0.15 (45)Ca-treated carotid arteries; P = .11), maximal intimal thickness (0.21 +/- 0.08 vs. 0.16 +/- 0.05; P = .12), average intimal thickness (0.12 +/- 0.06 vs. 0.08 +/- 0.03; P = .08), marginally significant reduction in percent area stenosis (33 +/- 15% vs. 21 +/- 9%; P = .06) and marked neointima suppression in areas immediately adjacent to 45Ca wrap remnants. Medial necrosis (P = .003), however, was observed slightly more for 45Ca-treated carotid arteries versus control arteries. CONCLUSION: Low-dose 45Ca beta-radiation labeled onto a polyurethane membrane appears to inhibit NIH in an animal model.

Angioplasty, Balloon↗
PubMedDate not supplied

Effects of off-centering on dose uniformity along and around blood vessels undergoing catheter-based intravascular brachytherapy.

PURPOSE: In intravascular brachytherapy, either photon or beta emitters are often used in a linear arrangement so that blood vessels of lengths in the range of several centimeters can be treated. With a line source, the dose uniformity and the range of doses that various components of the blood vessels receive depend not only on the type of radionuclides used in the treatment but also on the geometric position of radioactive source relative to the blood vessel walls. The aim of this study is to investigate the dose uniformity around the blood vessel and the effects on the uniformity due to the changes of the off-centering of different photon and beta emitters within the lumen. MATERIALS AND METHODS: Dose distributions were calculated on a cylindrical blood vessel of various radii. The radioactive sources of (192)Ir, (125)I, (103)Pd, (188)Re, (32)P, and (90)Y/Sr were studied. All the sources were assumed to be in the form of a line and had a length of 2 cm. The dose rate at a point in space produced by a radioactive source was computed by integrating the point dose rate kernel of the corresponding radionuclide over the 2-cm-long radioactive line. The point dose rate kernel was computed with Monte Carlo simulation of radiation transport. Dosimetric calculations were performed for both concentric and nonconcentric radioactive line source locations. Off-centering effects on the dosimetry were characterized with two newly defined quantities LDU and ADU: LDU describes the longitudinal dose uniformity along blood vessels and ADU describes the azimuthal dose uniformity, i.e., the dose deviation from the expected delivery dose around blood vessels. RESULTS: The longitudinal dose uniformity did not change significantly with the off-center distance. The azimuthal dose uniformity around the blood vessel deteriorated as the off-center distance increased. The ADU was worse for nonconcentric beta emitters than the photon emitters. For example, if the off-center distance was 1 mm and the radial distance was 1.5 mm, the range of dose around the blood vessel on the central transverse plane (normalized to the corresponding dose under the concentric condition) was from 0.55 to 3.3, 0.56 to 3.3, 0.53 to 3.4, 0.43 to 6.0, 0.38 to 4.3, and 0.31 to 4.7 for (192)Ir, (125)I, (103)Pd, (90)Y/Sr, (188)Re, and (32)P sources, respectively. However, it appeared that there existed a lower limit of underdosing (about 40% of desired delivery dose) caused by the off-centering for the photon emitters. It was also found that both ADU and LDU became almost independent of source length when the length was longer than or equal to 20 mm. CONCLUSIONS: A generalized formalism for expressing the dose uniformity along and around blood vessels generated with a linear source was developed and used to study the longitudinal and azimuthal dose uniformity for different types of radionuclides. Although concentric beta emitters provide uniform dose coverage along blood vessels, nonconcentric beta emitters produced larger dose deviations and worse dose uniformity around the blood vessels than photon emitters. The off-centering introduced significantly higher dose on proximal vessel walls for both beta and photon emitters; however, the underdosing at distal points due to off-centering was somewhat limited for the high-energy photon emitters. The magnitude of off-centering effects for the low-energy photon emitters ((103)Pd) was less than that for beta emitters but more than that for higher energy photon emitters ((125)I and (192)Ir).

Beta Particles↗
PubMedDate not supplied

Beta radiation in the treatment of in-stent restenosis of an in situ saphenous vein bypass graft A case report.

We describe a case of instent restenosis in a femoral-distal saphenous vein bypass graft successfully treated with brachytherapy. A 45-year-old insulin-requiring diabetic woman underwent an in-situ femoral-anterior tibial bypass graft for a non-healing ischemic ulcer. Despite a technically successful percutaneous transluminal angioplasty and endovascular stenting of a retained valve within the threatened graft, the wound failed to heal. At the 1-month follow-up, instent restenosis was documented and successful cutting balloon angioplasty, complemented by adjunctive beta-irradiation was successfully performed. Clinical and hemodynamic success was achieved, with prompt ulcer healing and intermediate-term graft patency maintained on surveillance duplex ultrasound follow-up. We review the literature on radiation therapy in the management of peripheral arterial disease and discuss therapeutic options in the management of restenosis.

Angioplasty, Balloon↗
PubMedDate not supplied

Intracoronary beta-irradiation prevents excessive in-stent neointimal proliferation in de novo lesions of patients with high plasma ACE levels. The BetAce randomized trial.

BACKGROUND: This study evaluated vascular brachytherapy (VBT) as a potent antiproliferative treatment to prevent in-stent restenosis (ISR) after coronary angioplasty of de novo lesions in patients carrying the D allele of the I/D polymorphism of the ACE gene and high ACE plasma levels (>34 U/l). METHODS AND MATERIALS: A prospective randomized trial was designed to detect a 30% improvement in the minimal lumen diameter (MLD) of the stenotic artery, as measured by quantitative coronary analysis (QCA), 6 months following VBT at the time of stented angioplasty. All patients were carriers of the D allele of the ACE gene, with plasma ACE levels >34 U/l. RESULTS: Thirty-one patients (33 stenoses) were allocated to stent implantation (control group) and 30 patients (31 stenoses) to VBT and stented angioplasty. After angioplasty, in-stent MLD was similar in the two groups. At 6 months in the control group, in-stent MLD had decreased to 1.74+/-0.8 versus 2.25+/-1.05 mm in the VBT group (P=.04). The mean in-stent diameter was 2.3+/-0.8 mm in the control group versus 2.9+/-1.05 mm after VBT (P=.02), and the restenosis rate was 37.5% versus 17.9%, respectively (P=.08). At 6 months, a higher need for target vessel revascularization (TVR) was observed in the control group: 35.5% versus 13.3% (P=.04). CONCLUSIONS: This randomized study confirms that patients with high plasma ACE concentrations are exposed to an increased risk for ISR after coronary stenting. The preventive use of VBT in these patients reduced neointimal formation by 65% such that the MLD at follow-up was increased by 29% compared with the control group.

Alleles↗
PubMedDate not supplied

Intracoronary radiation therapy using a novel beta emitter for in-stent restenosis Tungsten WRIST.

BACKGROUND: Intracoronary beta-radiation therapy reduces in-stent restenosis (ISR). We aimed to determine the safety and feasibility of intracoronary radiation therapy (IRT) utilizing tungsten (188W), a beta emitter. METHODS: A total of 30 patients with angiographic evidence of ISR in a previously treated native coronary artery underwent percutaneous coronary intervention (PCI; balloon angioplasty, ablation by atherectomy, or laser angioplasty). After the intervention, a noncentered delivery catheter with a side guide 0.014-in. wire carrying a tungsten (188W) coil, with an active length of 33 mm, was inserted. Patients were randomized to a radiation dose of 18, 22, or 25 Gy at 2 mm from the center of the source. Aspirin and Plavix, at 300 mg loading dose, were administered prior to intervention. Plavix 75 mg/day was prescribed for 6 months after the procedure. RESULTS: At 6 months follow-up, the overall binary angiographic restenosis rate was 18.8%. Target vessel revascularization (TVR) was 23% and target lesion revascularization related major adverse cardiac events (TLR-MACE) was 13.3%, without any intergroup differences. A comparison with the original Washington Radiation for In-stent restenosis Trial (WRIST) radiation cohort utilizing an 192Iridium source (prescription dose 15 Gy at 2 mm from the source) showed similar TVR and TLR-MACE rates of 30% and 18%, respectively. The TVR and TLR-MACE rates in the WRIST placebo cohort were 70% and 66%, respectively. CONCLUSIONS: Vascular brachytherapy with tungsten (188W) is feasible and safe. The 6-month clinical outcomes are similar to the original WRIST radiation group.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMedDate not supplied

IVUS-based dosimetry on patients with repeat-radiated coronary arteries to the same site.

BACKGROUND AND PURPOSE: Intracoronary radiation reduces recurrent in-stent restenosis (ISR). Repeat radiation may become necessary due to recurrent ISR. This study reports outcome-related dose calculations for twice-radiated coronary artery segments. MATERIALS AND METHODS: A total of 22 patients with angiographic evidence of ISR in a previously treated native coronary artery were assigned for repeat percutaneous coronary intervention and intravascular brachytherapy (IVBT). Intravascular brachytherapy was performed either with a 192Ir- or a 90Sr/Y-source (prescription dose: 14-18 and 23 Gy each at 2 mm from the center of the source), or a 32P-source (20 Gy 1-mm deep to the vessel wall). The mean time interval between the two IVBT treatments was 394+/-306 days. For each patient, angiograms and intravascular ultrasound cross sections were reviewed, on the basis of anatomical landmarks, matched, and the twice-radiated vessel segment identified. RESULTS: Clinical follow-up at 379+/-146 days revealed a target vessel revascularization rate of 18.2% and a target lesion revascularization rate of 13.6%. One death was reported. Maximal dose and average dose at the endothelium were 261 and 124+/-72.3 Gy, and maximal dose and average dose at the adventitia-media border were 159 and 50.3+/-29.3 Gy. Fourteen patients had 1.71 times longer recurrence-free interval compared to the interval between both IVBT treatments. CONCLUSIONS: Repeat IVBT to the same ISR site is safe without any adverse clinical events at an average 12 months' follow-up. A second IVBT treatment led to a prolonged ISR-free survival for the majority of patients. The choice of isotope did not influence outcome.

Beta Particles↗
PubMed2005

Long-term clinical outcomes of dissections after intracoronary beta-radiation with rhenium-188-diethylene triamine penta-acetic acid-filled balloon system.

BACKGROUND: Intracoronary radiation with a rhenium-188 ((188)Re)-filled balloon is safe and efficiently reduces restenosis, but there is a potential risk of a (188)Re-filled balloon induced dissection. Little is known about the effect of radiation on dissection resolution and the late clinical outcome of dissection after brachytherapy. METHODS: After successful catheter-based treatments of de novo or restenotic lesion, 256 patients were randomly assigned to the radiation or control group. The (188)Re-filled balloon system was designed to deliver 17.6 Gy in 1.0-mm tissue depth. RESULTS: Dissections were identified in 15 patients among the 138 patients of the radiation group (10.9%). Additional stents were deployed in 10 patients to cover the flow-limiting dissection. Binary restenosis rate (53.3% vs. 16.3%, p=0.001) and target vessel revascularization (TVR) rate (53.3% vs. 11.1%, p<0.001) were significantly higher in patients with the dissection at 9 months. Geographic miss (GM) was identified in 4 of the 10 patients who underwent additional stenting. Binary restenosis rate in the GM group (100%; 4 of 4 patients) was significantly higher than the non-GM group (33.3%; 2 of 6 patients, p=0.02). Long-term follow-up of the patients with dissections who had not undergone TVR (n=7, mean follow-up duration: 640.7+/-387.3 days) has demonstrated persistent unhealed dissections. CONCLUSIONS: Intracoronary radiation impairs the healing process after vessel injury and residual dissection after brachytherapy leads to adverse clinical outcomes, which was mainly due to GM in case of stent implantation.

Aged↗
PubMed2006

Determinants of model of renarrowing after beta radiation for in-stent restenosis.

UNLABELLED: It is unknown whether model of renarrowing after beta-radiation for in-stent restenosis (ISR) is influenced by the type of geographic miss (GM). METHODS: In 166 ISR treated with Galileo, serial quantitative coronary angiographic analysis was done. Minimal lumen diameters and lengths were measured for (1) stent, (2) peri-stent subsegments subjected to angioplasty with/without irradiation, and (3) irradiation margins. GM was defined as: (Type 1) edge injury within the 32P source dose fall-off: 2.0 mm inside and outside the source end marker or (Type 2) overt, nonirradiated injury: beyond the outer 2.0-mm long dose fall-off zone. RESULTS: Restenosis rate was 28.3% at 8.9+/-4.5 months with 60% located exclusively outside the stent. Type 1 GM was present in 24.7% of proximal edges, whereas Type 2 in 18.1%. Respective percentages for distal edges were 23.5% and 15.7%. Regardless of presence and type of GM, significant late lumen loss occurred only outside the stent. However, the biggest late lumen loss at the proximal edge was induced by the Type 1 GM (0.65+/-0.79, p<0.001), while proximal Type 2 GM was not associated with edge renarrowing (-0.04+/-0.48, p=NS). Both reference lumen diameter and proximal Type 1 GM influenced restenosis independently (OR 0.47; 95%CI 0.24-0.90; p=0.023 and OR 2.46; 95%CI 1.12-5.40; p=0.025). CONCLUSIONS: Regardless of presence and type of geographic miss, late lumen loss after beta-radiation occurs only outside the stent. However, injury within the proximal 32P dose fall-off but not overt edge injury is associated with the biggest late lumen loss at the respective edge, triggering recurrent restenosis.

Aged↗
PubMed2006

Beta-ray brachytherapy with 106Ru plaques for retinoblastoma.

PURPOSE: A retrospective analysis of 134 patients who received (106)Ru brachytherapy for retinoblastomas (175 tumors in 140 eyes). Treatment and follow-up were analyzed with special emphasis on tumor control organ, preservation, and late complications. RESULTS: Treated tumors had a mean height and diameter of 3.7+/-1.4 mm and 5.0+/-2.8 disk diameters, respectively. The radiation dose values were recalculated according to the calibration standard recently introduced by the National Institute of Standards and Technology. The recalculation revealed a mean applied dose of 419 Gy at the sclera (SD, 207 Gy) and 138 Gy (SD, 67 Gy) at the tumor apex. The 5-year tumor control rate was 94.4%. Tumor recurrence was more frequent in eyes with vitreous tumor cell seeding or fish-flesh regression. The estimated 5-year eye preservation rate was 86.5%. Previous treatment by brachytherapy or external beam radiotherapy, as well as a large tumor diameter, were significant factors for enucleation. The radiotherapy-induced complications after 5 years of follow-up were retinopathy (22%), optic neuropathy (21%), and cataract (17%). These complications were significantly more frequent after prior brachytherapy or external beam radiotherapy. CONCLUSION: Brachytherapy using (106)Ru plaques is a highly efficient therapy with excellent local tumor control and an acceptable incidence of side effects.

Adolescent↗