Histomorphometric evaluation of (198)Au endovascular brachytherapy in a renal artery restenosis model in rabbits

OBJECTIVE: The main mid-term complication of percutaneous transluminal angioplasty of the renal artery is restenosis, which occurs in up to 50% of patients. Although no pharmacologic agent to date has been effective in preventing restenosis, both beta-ray emitters and gamma-ray emitters used in endovascular brachytherapy have been shown to reduce coronary restenosis. The objectives of this study were to evaluate the efficacy of (198)Au endovascular brachytherapy in preventing restenosis after percutaneous transluminal renal angioplasty and to determine the radiation dose to the operator. MATERIALS AND METHODS: Twenty-one New Zealand white rabbits (10 females and 11 males) weighing an average of 3.5 kg (range, 3.2-3.8 kg) who had been fed a normal diet underwent bilateral 33% overdilatation with deendothelialization of the renal arteries. After 7 weeks, the induced renal artery stenoses were treated by percutaneous transluminal renal angioplasty. The rabbits were randomly assigned to one of three groups before receiving endovascular 25-Gy irradiation at a radial 2.0-mm depth with a 0.5 x 15 mm (198)Au wire (106 MBq). The right renal artery was irradiated in group A; the left, in group B. The rabbits in group C randomly received a right- or left-sided dummy wire. Operator exposure to radiation was measured using thermoluminescent dosimeters and ionization chambers. The rabbits were sacrificed after 3 weeks. The aorta and renal arteries were perfusion-fixed. The renal arteries were removed for histologic and histomorphometric study. RESULTS: Forty-two renal arteries were cut into a series of 4- micro m-thick slices. Five arteries were thrombosed (two in the irradiated group and three in the control group, p > 0.05). In the patent arteries (n = 37), the average neointimal area was 0.068 mm(2) (range, 0.009-0.234 mm(2)) in 15 irradiated segments (315 slices total), whereas the average neointimal area was 0.135 mm(2) (range, 0.016-0.324 mm(2)) in 22 control segments (462 slices total) (analysis of variance, p < 0.009), showing a percentage area of restenosis of 10.4% in irradiated arteries and 43.4% in non-irradiated arteries (p < 0.0003). Radiation dose per procedure to the operator was 0.034 mSv in the index finger, 0.024 mSv in the wrist, and undectable in the body. CONCLUSION: Endovascular brachytherapy with (198)Au appears to inhibit early renal artery restenosis and exposes the operator to a safe level of radiation.     

Bremsstrahlung radiation exposure from pure beta-ray emitters.

With increasing therapeutic use of radionuclides that emit relatively high-energy (>1 MeV) beta-rays and the production in vivo of bremsstrahlung sufficient for external imaging, the potential external radiation hazard warrants evaluation. METHODS: The exposure from a patient administered beta-ray-emitting radionuclides has been calculated by extending the National Council on Radiation Protection and Measurement model of a point source in air to account for biologic elimination of activity, the probability of bremsstrahlung production in vivo and its mean energy and the absorption by the patient's body of the bremsstrahlung thus produced. To facilitate such calculations, a quantity called the "specific bremsstrahlung constant" (in C/kg-cm2/MBq-h), betaBr, was devised and calculated for several radionuclides. The specific bremsstrahlung constant is the bremsstrahlung exposure rate (in C/kg/h) in air at 1 cm from a 1 MBq beta-ray emitter of a specified maximum beta-ray energy and frequency of emission in a medium of a specified effective atomic number. RESULTS: For pure beta-ray emitters, the retained activities at which patients can be released from medical confinement (i.e., below which the effective dose equivalent at 1 m will not exceed the maximum recommended value of 0.5 cSv for infrequently exposed members of the general public) are extremely large: on the order of hundreds of thousands to millions of megabecquerels. CONCLUSION: Radionuclide therapy with pure beta-ray emitters, even high-energy beta-ray emitters emitted in bone, does not require medical confinement of patients for radiation protection.     

mBAND analysis of chromosome aberrations in lymphocytes exposed in vitro to alpha-particles and gamma-rays

PURPOSE: To investigate the profiles of chromosome damage induced in vitro by exposure to alpha-particles and gamma-rays. MATERIALS AND METHODS: Human peripheral blood lymphocytes were exposed to three dose regimes: alpha-particle doses of 0.2 and 0.5 Gy and a gamma-ray dose of 1.5 Gy. After culturing for 47 hours, chromosome aberrations involving the number 5 chromosomes were identified using a multi-coloured banding (mBAND) technique. RESULTS: Analysis of the frequencies of chromosome 5 breaks within aberrant cells and within aberrant number 5 chromosomes demonstrated that alpha-particle irradiation is more likely to result in multiple breaks in a chromosome than gamma-irradiation. Additionally, overdispersion was observed for all doses for the distribution of breaks amongst all cells analysed and breaks amongst total number 5 chromosomes, with this being greatest for the 0.2 Gy alpha-particle dose. The ratio of interchanges to intrachanges (F ratio) was 1.4 and 2.4 for 0.2 and 0.5 Gy alpha-particles respectively and 5.5 for 1.5 Gy gamma-rays. Evaluation of simple versus complex exchanges indicated ratios of 1.9 and 2.7 for 0.2 and 0.5 Gy alpha-particles respectively and 10.6 for 1.5 Gy gamma-rays. The majority of the intrachanges involving chromosomes 5 induced by alpha-particle radiation were associated with more complex exchanges. CONCLUSIONS: This study has confirmed that exchanges induced by exposure to high linear energy transfer (LET) alpha-particle radiation comprise a greater proportion of intrachanges than those induced by exposure to low LET gamma-rays. However, since the majority of these are associated with complex rearrangements and likely to be non-transmissible, this limits their applicability as a marker of past in vivo exposure.     

β源支架剂量分布的蒙特卡罗算法

目的 比较数值积分和蒙特卡罗方法计算的放射性支架的剂量率分布。方法 以3种有代表性的剂量点核函数为计算模型，计算支架的剂量率分布。结果 分别计算了中心面的径向，支架表面及离支架表面0.5mm处的轴向剂量分布，径向最大差异为1．5％，轴向的差异也有1．5％之内。结论 3种函数用数值积分和蒙特卡罗方法计算的剂量分布是一致的，蒙特卡罗方法可用来计算放射性支架的剂量分布。     

裂变中子照射小鼠脾脏NK活性和IL－2产生能力的变化

研究了裂变中子照射对小鼠脾脏ＮＫ活性和ＩＬ－２产生能力的剂量效应关系，并与γ线作了比较。裂变中子照后２４ｈＮＫ活性的量效曲线不典型：低剂量时明显下降，１．５—５．５Ｇｙ时高于正常，以后又下降。以Ｄ＿（３７）或Ｄ＿０为指标，中子相对生物学效应（ＲＢＥ）分别约为１．７和１．６。脾细胞ＩＬ－２产生能力对裂变中子和γ线的辐射反应相近，Ｄ＿（３７）均约为２．５Ｇｙ，裂变中子ＲＢＥ为１。     

Ⅰ~ⅡB期精原细胞瘤术后放疗中不同厚度低熔点挡铅对睾丸剂量防护的研究

目的 评估精原细胞瘤术后放疗中低熔点挡铅厚度及与射野边缘的距离对健侧睾丸受照剂量的影响。方法 选取1例I期精原细胞瘤术后患者的放射治疗计划,利用Synergy医用直线加速器6 MV X射线在SZMC-IV型仿真人体模型上模拟患者照射。采用PTW 0.6 cm³指型电离室,在距射野边缘不同距离处分别测量无挡铅和有3、5、7、10及15 mm厚度低熔点挡铅屏蔽条件下的吸收剂量,评价不同条件下的剂量防护效果。结果 在上述各挡铅厚度条件下,测量结果的归一化剂量与测量点离射野边界之间的距离呈指数形式衰减。无挡铅时的测量结果相对于靶区处方剂量,由距离射野边缘1 cm处的8.41%降到25 cm处的0.61%。有3、5及7 mm挡铅时,分别由距离射野边缘1 cm处的4.55%、3.98%及3.47%降到25 cm处的0.27%、0.21%及0.17%。有10 mm挡铅时,由距离射野边缘1.5 cm处的2.55%降到25 cm处的0.15%。有15 mm挡铅时,由距离射野边缘2 cm处的1.86%降到25 cm处的0.13%。在处方剂量为26 Gy并且距离射野边缘10 cm或4 cm以上,和处方剂量为36 Gy并且距离射野边缘4 cm以上的条件下,分别采用3、7和15 mm厚度的挡铅屏蔽,能将睾丸的散射剂量降低到0.5 Gy以下。结论 在精原细胞瘤术后常规放疗中,根据不同的处方剂量和照射野范围,采用低熔点铅自制适当厚度的睾丸防护装置,能方便、有效地降低睾丸受照剂量,有利于保护患者的生育能力。     

A new experimental determination of the dose calibrator setting for 188Re.

Accurate activity measurements of radionuclides using commercial dose calibrators requires that the correct dial setting (or calibration factor) be applied. The dose calibrator setting for the medical radionuclide 188Re (as 188ReO4-) has been determined experimentally using solution sources prepared and calibrated at the National Institute of Standards and Technology (NIST). METHODS: The specific activity of two sources (in units of MBq/g) in the standard 5-mL NIST ampoule and in a 5-mL SoloPak dose vial were calibrated using 4pibeta liquid scintillation counting with 3H-standard efficiency tracing and gamma-ray/bremmstrahlung counting in the NIST "4pi" gamma ionization chamber on gravimetrically related sources. RESULTS: The newly determined settings for the NIST Capintec CRC-12 dose calibrator are (631+/-4) x 10 and (621+/-3) x 10 for the respective ampoule and dose vial geometries with an expanded (at a presumed 95% confidence level) uncertainty of 0.4%-0.5% in the activity determination. The setting for the dose vial geometry was independently confirmed using a Capintec CRC-15R at Cedars-Sinai Medical Center using sources calibrated against a NIST standard. CONCLUSION: These new settings result in activity readings 28%-30% lower than those obtained using the previously recommended setting of 496 x 10. This discrepancy most likely results from underestimating the total radiation yield from 188Re decay when calculating the dose calibrator response. This study emphasizes the need for experimental determinations of dose calibrator settings in the geometry in which the measurements will be performed.     

被覆金属内支架治疗食管气管瘘的随访研究

目的;探讨被覆内支架治疗食管癌病人食管气管瘘的远期疗效及并发症。方法：１５例在Ｘ线电视导上置入被覆内支架１５个,１０例门诊随访,５例电话或信访。结果：１５例均一次封闭成功,平均生存期６．４５月,其中６例联合放化疗生存期平均为９．２月,９例死于肿瘤转移,３例死于肺部感染,３例死于其它原因,１例支架滑脱入胃内,１例支架上端再狭窄,１例食物堵塞支架上端,３例有明显胃食管返流,余无明显并发症。结论：被覆     

Dose verification of virtual bolus application for helical tomotherapy

The objective of the study is to verify the dose delivered on helical tomotherapy based on treatment plan with varying virtual bolus (VB) thickness. The target was localized on the ArcCHECK image by 3 mm margin from the phantom surface. The dimension of target, which includes the ArcCHECK's detectors, with the 4.0 cm width and length 12.0 cm along the phantom The 5 treatment plans were generated, 1 plan without VB application (NoVB) and the 4 plans with varying of VB thickness on the phantom surface by 0.5 cm (VB0.5), 1.0 cm (VB1.0), 1.5 cm (VB1.5), and 2.0 cm (VB2.0), in treatment planning but absent during irradiation. For measurement analysis, the ionization chamber and the ArcCHECK detectors were used for point dose and dose distribution by investigating the percentage of dose difference and the gamma passing rate. The VB thickness 0.5, 1.0 and 1.5 cm showed acceptable value with less than 2% for dose difference by 0.37% (VB0.5), -0.11% (VB1.0) and -0.37% (VB1.5) at the center of ArcCHECK. The accuracy of dose distribution showed an acceptable gamma passing rate of 99.8% (VB0.5), 100% (VB1.0), and 90.2% (VB1.5) for gamma criteria by 3%/3mm for absolute dose analysis. However, the gamma passing rate of VB2.0 down to 71.2% of absolute mode for gamma criteria by 3%/3mm. The treatment plans with VB thickness less than 15 mm deliver doses that are comparable to treatment plans without virtual bolus based on gamma analysis. However, the deviation showed a trend increasing when VB thickness increased. The VB2.0 was not acceptable for point dose and dose distribution verification by more than 2% dose difference and less than 90% of gamma passing rate.     

Technical management of a pregnant patient undergoing radiation therapy to the head and neck.

The fetal dose in a pregnant patient undergoing radiation therapy to the head and neck region was investigated. Implicit in this study was the design and evaluation of a shield used to minimize the fetal dose. To evaluate the fetal dose, a phantom was irradiated with the fields designed for this patient's therapy. The peripheral dose was measured for each field individually, both without and with a custom shield designed to be placed about the patient's abdominal and pelvic regions. The total dose at the location of the fetus over the course of this patient's radiation therapy was then estimated from peripheral dose rate measurements made at several points within the simulated uterus. With no shielding, the total dose within the uterus of the patient would have ranged from 13.3 cGy at the cervix to 28 cGy at the fundus. With the shield applied, the uterine dose was significantly less: 3.3 cGy at the cervix to 8.6 cGy at the fundus. In fact, at every measurement point, the peripheral dose with the shield in place was 30% to 50% of the dose without the shield. Some data suggest that the rate of significant abnormalities induced by irradiation in utero increases with increasing dose within the range of total peripheral doses incurred during most radiation treatment courses. It is therefore prudent to make reasonable attempts at minimizing the dose to the lower abdominal and pelvic regions of any pregnant patient. The shield designed in this work accomplished this goal for this patient and is flexible enough to be used in the treatment of almost all tumor volumes.     

Noninvasive inductive stent heating: alternative approach to prevent instent restenosis?

RATIONALE AND OBJECTIVES: To test noninvasive inductive heating of implanted vascular stents as an alternative approach for reduction or prevention of neointimal hyperplasia. METHODS: Calorimetric pretests were performed to get an orientation on the different parameters of influence for inductive heating of stents. The field strength was set to a maximum of 90 kA/m within a frequency range from 80 kHz to 320 kHz. The electromagnetic field was emitted by a custom-made water-cooled copper winding antenna. A flow model for stent heating was set up to assess the increase in temperature of an expanded 316L stainless steel stent with typical coronary stent dimensions of 3.5 mm diameter and 14.5 mm in length, and in a second setup with 4.5 mm diameter and 13 mm in length, respectively. The stent was located in a bioartificial artery, simulated by a fibrinogen matrix with a defined number of vital cells. The system was exposed to a pulsating perfusion and to an electromagnetic field of 200 kHz over a period of 20 minutes and in a second setup to an electromagnetic field of 300 kHz and increasing intensity up to maximum power-output. Afterward, the artificial vessel was sliced and examined by fluorescence microscopy to evaluate the number and location of damaged cells. RESULTS: The calorimetric tests show an exponential correlation of energy uptake in the stent with an increase in frequency and a constant generator output. At a frequency of 80 kHz, the power uptake accounts for 0.1 W (250 kHz 1.0 W; 320 kHz 1.9 W, respectively). The flow tests confirmed feasibility to elevate the stent temperature from 37 degrees C body temperature to 44 degrees C at 200 kHz within 55 seconds. The temperature increase of the fluid passing the heated vessel region was only marginal (maximum of 0.5 degrees C). Cell necrosis after 20 minutes of treatment was not observed. In a second set-up with 4.5 mm stent diameter, a frequency of 300 kHz and with maximum power output, the stent temperature was increased to 80 degrees C and there was extensive necrosis area around the stent. Treatment time and stent temperature were optimized in further tests. CONCLUSION: Selective noninvasive energy transfer to coronary stainless steel stents by inductive heating is possible within a wide range of power. By thermal conduction, vital cells close to the stent struts can be affected. The frequency of 200 kHz turned out to be favorable. There is still room for further optimization of energy dosage with regard to material and stent design, to induce controlled cell death. The method has potential to serve as an alternative approach for prevention of instent restenosis.     

硅膜-镁合金可降解支架置入兔食管可行性及组织反应——外和体内初步研究

目的 体外研究硅膜-镁合金可降解支架的机械特性和降解行为,体内研究其置入兔食管的可行性及组织反应.方法 体外测试硅膜-镁合金可降解支架的机械压缩恢复性能和降解行为.30只健康荷兰兔随机分为硅膜-镁合金支架组(n=15,透视导引下将支架置入兔食管下1/3段)和对照组(n=15,未作任何干预),支架置入后1、2、4周两组兔分别接受食管造影,同时于各时间点分别处死5只兔,取材作组织学检查.结果 体外测试显示硅膜-镁合金可降解支架表现出良好的柔韧性和弹性,在pH4.0、pH7.4磷酸缓冲液中降解均慢于镁合金裸支架;体内测试显示支架置入后所有实验兔耐受性良好,食管直径在置入前为(9.2±0.8) mm,置入后1、2、4周分别为(9.7±0.7)mm、(9.6±0.8)mm、(9.6±0.5)mm(P＞0.05).支架组6只兔发生支架移位(1周时1只,2周时1只,4周时4只).支架组食管上皮、平滑肌层变薄等食管壁重建与对照组比较,差异有统计学意义(P＜0.05);支架置入后食管壁损伤及胶原沉积等组织反应与对照组比较,差异无统计学意义(P＞0.05).结论 硅膜-镁合金可降解支架置入兔食管技术上可行,可提供至少2周支撑力,支架移位率可接受,未发生严重食管壁损伤及胶原沉积.     

Long-term safety of cardiac magnetic resonance imaging performed in the first few days after bare-metal stent implantation

PURPOSE: To investigate the long-term safety of cardiac magnetic resonance imaging (CMR) performed one to seven days after coronary artery stent (bare metal) implantation. MATERIALS AND METHODS: We analyzed 119 consecutive patients with acute myocardial infarction (MI) who underwent emergency coronary stent implantation with a bare-metal stent. CMR using a 1.5T scanner was performed on 51 patients (42.9%) at a mean of 2.7+/-3.1 days after stent implantation (CMR+ group), and the remaining 68 patients (57.1%) served as controls (CMR- group). The patients were followed up to six months for major adverse cardiac events. RESULTS: The average stent size was 3.3+/-0.5x18.4+/-6.7 mm, and 86% of the stents were made of 316L stainless steel. There were no significant differences between the CMR+ and CMR- groups in terms of infarct features, angiographic findings, or stent characteristics. Over a mean follow-up of 4.4+/-2.1 months, 12 patients (10.1%) had 16 events (13.4%). Two patients had adverse events after early MRI scan (4.3%), a rate that is lower than the event rate in the patients who did not undergo MRI (16%, P=0.04), and one of the two events was clearly not MRI related. CONCLUSION: CMR on a 1.5T scanner can be safely performed within one to seven days after coronary bare-metal stent implantation and is not associated with an increased risk of adverse clinical cardiac outcomes. In the light of accumulating data, the guidelines by stent manufacturers should be revised.     

儿童颅脑外伤CT扫描参数的优化设置

目的研究儿童头颅外伤患者CT扫描参数的设置。在不影响影像诊断的前提下,尽可能降低辐射剂量。方法用不同的CT扫描参数对随机分组的小儿进行扫描,有3个变量电压分为120、140kV;毫安状态分为normal、low;层厚分为7、10mm。分别组合成8组不同的扫描参数组。记录各组的辐射计量(权重CT剂量学指数,CTDIW);用CT值的标准差和诊断阳性率作为图像质量的主客观标准进行分析。结果①在自动mA状态下,140KV比120KV剂量平均降低22.7%;降低毫安状态从normal到low可使剂量降低18.1%;选择较大层厚10mm比7mm辐射剂量平均降低19.7%;若同时同向改变参数,辐射剂量最大可减少近50%。②各组之间图像质量的CT值标准差(CTsd)和CT诊断阳性率的差异无显著性意义。结论用高KV、低毫安状态(low)、较大层厚均可以降低辐射剂量,且图像质量对诊断没有影响。因此对于外伤患者建议用140KV、自动mAs的低毫安状态(low)和10mm层厚为最佳扫描方式。     

Post-stenting intravascular brachytherapy trials on hypercholesterolemic rabbits using 32P liquid sources: implications for prevention of in-stent restenosis

PURPOSE: Liquid sources of radiation delivered in angioplasty balloons may be a convenient self-centering device used for prevention of in-stent restenosis. To test the effectiveness of this method an intravascular brachytherapy study was performed using 32P liquid sources in an animal model. METHODS: The radial dose distribution around angioplasty balloons filled with solutions of Na 2H 32PO 4 was calibrated by thermoluminescence dosimetry. The animal experiments were performed in rabbits with induced hypercholesterolemia. The balloons containing 32P were introduced into iliac arteries immediately after stent implantation. Estimated 7-49 Gy doses required 30-100 min irradiations. Radiation effects were evaluated by comparing the thickness of various components of the artery wall. RESULTS: Doses of 7, 12, 16 or 49 Gy on the internal artery surface required 30-100 min of irradiation. The dose of 49 Gy at "zero" distance corresponding to 16 Gy at 1.0 mm from the balloon surface reduced hypertrophy in every layer of the arterial wall: in the intima the cross-sectional areas were 0.13 versus 0.91 mm 2, in the media were 0.5 versus 0.46 mm 2 and in the adventitia were 0.04 versus 0.3 mm 2 (p <0.05). A dose of 7 Gy at the balloon surface produced adverse irradiation effects: the intimal area of the artery was 2.087 versus 0.857 mm 2, the medial area was 0.59 versus 0.282 mm 2 and the adventitial area was 0.033 versus 0.209 mm 2 in treated and control arteries, respectively. CONCLUSION: Application of a 49 Gy irradiation dose to the internal arterial surface effectively prevented in-stent restenosis.     

Three-dimensional dose distribution for partial irradiation of rat parotid glands with 200kV X-rays

PURPOSE: To investigate dose distributions in partial-volume irradiation experiments in small experimental animals, in particular the parotid gland of rat. MATERIALS AND METHODS: High-resolution magnetic resonance imaging images were made that provided the outlines of the parotid glands, which were used to design collimators with conformal radiation ports for 100 and 50% cranial/caudal partial-volume irradiation. A protocol for absolute dosimetry was designed and relative dose measurements were performed. From the three-dimensional topographical data and the three-dimensional dose distribution, dose-volume histograms were determined. RESULTS: The standard uncertainty of absorbed entrance dose was within 3%. Radiochromic film, thermoluminescence dosemeters and ionization chamber dose measurements revealed that the relative doses measured were in good agreement. The 20-80% penumbra of the beam across the 50% field edge was only 0.4 mm at a 6 mm depth. The gradient of the percentage depth dose from the skin of the rat to a depth of 12 mm was 1.5% mm(-1). The absorbed doses in the cranial 50% and the caudal 50% partial volumes were comparable. This finding was reflected in the calculated dose-volume histograms of the different regions, which were similar. The dose in the shielded area between the left and right ports was about 14% of the dose near the centres of the beams. CONCLUSION: The designed set-up showed that irradiation of small volumes could be performed with high accuracy allowing the study of differences in radiation damage. Similar doses were given to the 50% cranial and 50% caudal gland volumes and, therefore, a possible difference in radiosensitivity in these volumes was not a dose effect. The approach used was also applicable for the irradiation of small volumes of other tissues.     

Esophageal carcinoma: evaluation with high-resolution three-dimensional constructive interference in steady state MR imaging in vitro

PURPOSE: To determine the usefulness of high-resolution three-dimensional (3D) constructive interference in steady state (CISS) MRI for evaluating mural invasion and morphologic features in esophageal carcinomas. MATERIALS AND METHODS: Twenty-four esophageal specimens with carcinomas were studied with a 1.5-T system using a 4-cm-diameter loop coil. High-resolution 3D-CISS MR images were obtained with a field of view (FOV) of 80 mm, matrix of 256 x 256, and section thickness of 0.5 mm (voxel size of 0.05 mm(3)). 3D-CISS MR images were compared with histopathologic findings, and virtual MR endoscopic images were compared with macroscopic findings at surgery. RESULTS: 3D-CISS MR images clearly depicted the normal esophageal wall as consisting of eight layers, which correlated well with the histologic layers. In 22 of 24 esophageal carcinomas (92%), the depth of mural invasion visualized with 3D-CISS MRI correlated well with the histopathologic staging. In all 24 carcinomas (100%), virtual MR endoscopic images clearly depicted the macroscopic types of the carcinomas, including adjacent lymph node swelling. CONCLUSION: High-resolution 3D-CISS MRI has a high diagnostic accuracy for evaluating mural invasion and macroscopic findings in esophageal carcinomas, and may be applicable to preoperative histopathologic staging and morphologic evaluation.     

Inhibition of neointimal proliferation with 188Re-labeled self-expanding nitinol stent in a sheep model

PURPOSE: To evaluate a self-expanding rhenium 188 (188Re) radiochemically labeled radioactive stent in sheep. MATERIALS AND METHODS: A self-expanding nitinol stent (30 mm in length, 8 mm in diameter) coated with a functionalized polymer layer was radiolabeled with 188Re. Fifty prostheses, 25 of which were radioactive (mean radioactivity, 20 MBq +/- 3.8 [SD]) and 25 of which were nonradioactive, were implanted into the external iliac arteries of 25 sheep. Stent patency was assessed with angiography. Neointimal formation was assessed with intravascular ultrasonography and histologic examination 1 month (in all sheep) and 3 months (in 12 sheep) after implantation. The results were analyzed by using repeated-measures analysis of variance with two repeated factors and paired t tests for comparison at each measuring point. RESULTS: All stents were placed successfully. Data in one animal had to be excluded from the study. After 3 months, a mean neointimal area reduction of 70 mm2 +/- 55 (SD) was observed inside the radioactive stents, and a mean lumen reduction of 126 mm2 +/- 39 was observed inside the nonradioactive control stents (P =.022). An edge effect was observed in the radioactive stents in that they showed an amount of neointimal formation at the edges that was similar to that seen in control stents. This neointimal formation accounted for the maximum lumen loss in the vascular segment with the stent. CONCLUSION: As compared with a nonradioactive stent, a beta particle-emitting stent, through endovascular irradiation, significantly inhibits neointimal formation inside the stent but not at the stent edges.