Inhibition of neointimal hyperplasia after stent placement with rhenium 188-filled balloon dilation in a canine iliac artery model

PURPOSE

To evaluate the efficacy of beta-irradiation therapy with rhenium 188 ((188)Re) mercaptoacetyltriglycine (MAG3)-filled balloon dilation to prevent neointimal hyperplasia after stent placement in a canine iliac artery model.

MATERIALS AND METHODS

A total of 15 stents were implanted into the iliac arteries of eight dogs (one or two stents in each dog). Rhenium 188 MAG3-filled balloon dilation was performed immediately after placement of 10 bare stents-20 Gy in group II (n = 5) and 40 Gy in group III (n = 5)-and conventional balloon dilation was performed immediately after placement of the remaining five bare stents (group I). A follow-up angiogram was obtained 8 weeks after the procedure, and percentage of luminal stenosis was calculated for the proximal and distal ends of each stent. Neointimal thickening (expressed as the neointimal area divided by the sum of neointimal area and media area) was assessed for microscopic examination.

RESULTS

All eight dogs survived until they were euthanized 8 weeks after the procedures. The mean luminal stenosis measurements at 8-week follow-up angiography in groups I, II, and III were 26.63%, -0.44%, and 10.53%, respectively. The mean neointimal thickening measurements in groups I, II, and III were 0.77, 0.21, and 0.34, respectively. The mean percentage of luminal stenosis and neointimal thickening differed significantly among the three groups (P < .05).

CONCLUSIONS

beta-Irradiation with (188)Re-MAG3-filled balloon dilation has the potential to reduce neointimal hyperplasia secondary to stent placement in a canine iliac artery model. A dose of 20 Gy may be preferable versus a dose of 40 Gy to reduce neointimal hyperplasia.

A meta-analysis of randomized controlled trials of intracoronary gamma- and beta-radiation therapy for in-stent restenosis

We assessed the effectiveness of intracoronary brachytherapy and compared treatment effects for the two radiation sources as well as the performance of the procedure in saphenous vein grafts (SVG) and native coronary arteries. Five randomized controlled trials comparing intracoronary brachytherapy with placebo involving a total of 1310 patients were reviewed for a meta-analysis. Risk differences (RD) for major adverse cardiac events (MACE), target vessel revascularization, target lesion revascularization, and angiographic binary restenosis at 6-12 months were computed, and a meta-regression analysis of MACE was performed. For MACE, the RD was 0.19 (95% confidence interval [CI], 0.09%-0.29%; P value, 0.00); there was significant between-study variance of 0.2395. In univariate meta-regression analyses, diabetes was a significant factor for the between-study variance (P value, 0.000). In multivariate meta-regression analyses adjusted for diabetes and lesion length, neither gamma-radiation source nor SVG was a significant factor for the between-study variance (P value, 0.675 and 0.433, respectively); the adjusted between-study variance was 0.000. Intra-coronary brachytherapy is effective compared with placebo at mid-term follow up. Neither procedure in SVG (gamma radiation) nor difference in radiation source (beta or gamma) in native coronary arteries was a significant factor in brachytherapy effectiveness compared to placebo.

Intravascular brachytherapy versus drug-eluting stents for the treatment of patients with drug-eluting stent restenosis

Drug-eluting stents (DESs), although promising technology, still are associated with restenosis; therefore, we evaluated the safety and efficacy of intravascular radiation therapy for the treatment of DES in-stent restenosis (ISR). Treatment of DES ISR has not been established, although intravascular radiation therapy is an effective treatment for patients with ISR of bare metal stents. Other modalities are conventional percutaneous coronary intervention (PCI), including restenting with DES. Radiation for Eluting Stents in Coronary FailUrE (RESCUE) is an international, Internet-based registry of 61 patients who presented with ISR of a DES and were assigned to intravascular radiation therapy with commercially available systems after PCI. Outcomes of these patients were compared with those of a consecutive series of 50 patients who presented with ISR of a DES and were assigned to repeat DES (r-DES) treatment. Baseline clinical and angiographic characteristics were similar between groups, except for more Cypher stents as the initial DES that restenosed in the r-DES group than in the intravascular radiation therapy group (88.5% vs 69%, p = 0.01). At 8 months there were fewer overall major adverse cardiac events in the intravascular radiation therapy group compared with the r-DES group (9.8% vs 24%, p = 0.044). The need for target vessel and target lesion revascularizations was similar in the 2 groups at 8 months. There has been no report of subacute thrombosis in either group. In conclusion, intravascular radiation therapy as adjunct therapy to PCI for patients presenting with ISR of a DES is safe and should be considered an alternative therapeutic option for this difficult subset of patients.

BRAVO I: A pilot study of vascular brachytherapy in polytetrafluoroethylene dialysis access grafts

Hemodialysis vascular access dysfunction owing to stenosis and thrombosis in polytetrafluoroethylene dialysis access grafts is a huge clinical problem for which there are currently no long lasting durable therapies. Vascular brachytherapy has been used successfully for the prevention of coronary restenosis following angioplasty and stent placement. The Beta Radiation for Treatment of Arterial-Venous Graft Outflow I study was a pilot study of vascular brachytherapy in hemodialysis patients with patent but dysfunctional grafts. Twenty-five patients were randomized to receive either radiation therapy (a single dose of 18.4 Gy) or sham radiation, following angioplasty. The primary efficacy end point of the study was target lesion primary patency at 6 months. The primary safety end point was a composite of death, emergency surgery on the graft, venous rupture, or aneurysm formation. Forty-two percent of the radiated grafts achieved the target lesion primary patency end point at 6 months as compared to 0% of the control group (P = 0.015), but this did not translate into an improvement in secondary patency at either 6 or 12 months. Radiation therapy was found to be safe in the setting of hemodialysis vascular access dysfunction. Our results suggest that vascular brachytherapy is an intervention that is worthy of further examination in the setting of non-thrombosed dialysis access grafts.

Intracoronary β-brachytherapy using a rhenium-188 filled balloon catheter in restenotic lesions of native coronary arteries and venous bypass grafts

PURPOSE

We have previously demonstrated the efficacy of intracoronary beta-brachytherapy using a liquid (188)Re-filled balloon in a randomised trial including de novo lesions. Percutaneous coronary interventions in restenotic lesions and in stenoses of venous bypass grafts are characterised by a high recurrence rate for restenosis and re-interventions. Against this background, we wanted to assess the impact of intracoronary beta-brachytherapy using a liquid (188)Re-filled balloon in restenotic lesions in native coronary arteries and venous bypass grafts.

METHODS

In 243 patients, beta-brachytherapy with 22.5 Gy was applied at a tissue depth of 0.5 mm. Patients were followed up angiographically after 6 months and clinically for 12 months. The primary clinical endpoint was the incidence of MACE (death, myocardial infarction, target vessel revascularisation). Secondary angiographic endpoints were late loss and binary restenosis rate in the total segment.

RESULTS

All irradiation procedures were successfully performed. A total of 222 lesions were in native coronary arteries; 21 were bypass lesions. Mean irradiation length was 41.6+/-17.3 mm (range 20-150 mm) in native coronary arteries and 48.1+/-33.9 mm (range 30-180 mm) in bypass lesions; the reference diameter was 2.57+/-0.52 mm and 2.83+/-0.76 mm, respectively. There was no vessel thrombosis during antiplatelet therapy. Angiographic/clinical follow-up rate was 84%/100%. MACE rate was 17.6% in the native coronary artery group and 38.1% in the CABG group (p<0.03). Binary restenosis rate was 22.5% and 55.6% (p<0.01), and late loss was 0.38+/-0.72 mm and 1.33+/-1.11 mm (p<0.001), respectively.

CONCLUSIONS

We conclude that intracoronary beta-brachytherapy with a liquid (188)Re-filled balloon using 22.5 Gy at a tissue depth of 0.5 mm in restenotic lesions is safe. It is associated with a low binary restenosis rate, resulting in a low occurrence rate of MACE within 12 months in restenotic lesions in native coronary arteries but not in vein grafts.

Clinical Results of Intracoronary Brachytherapy (ICBT) for Multiple In-Stent Restenosis

BACKGROUND AND PURPOSE

Treatment of in-stent restenosis (ISR) with percutaneous coronary intervention (PCI) alone is often followed by early re-restenosis. The present study focused on the effect of intracoronary brachytherapy (ICBT) on multiple in-stent restenosis (MISR) after repeated PCI.

PATIENTS AND METHODS

40 patients (27 male, 13 female, age: 66 +/- 9 years) with MISR (two to six ISRs, median three ISRs) were retrospectively analyzed. All patients were treated by using the Novoste((R)) Beta-Cathtrade mark 3.5F System after PCI. The target vessel received 18.4-25.3 Gy of radiation at a depth of 2 mm from the center of the source. The restenosis-free survival and overall survival were calculated by Kaplan-Meier analysis (log-rank). The time interval between last PCI without ICBT and the consecutive recurrence was compared with the follow-up time after PCI with ICBT.

RESULTS

The 3-year overall survival rate after ICBT was 93%. The 0.5-, 1-, 2-, and 3-year ISR-free survival rates after PCI + ICBT were 81%, 72%, 52%, and 38%, respectively. After PCI alone, the 0.5-, 1-, and 2-year ISR-free survival rates were 30%, 13%, and 0%, respectively. This difference was highly significant (p < 0.0001). Patients with more than three ISRs before ICBT had a better outcome (3-year ISR-free survival: 80%) than patients with only two or three ISRs before ICBT (3-year ISR-free survival: 25%; p < 0.05).

CONCLUSION

ICBT is highly effective and safe in patients with ISR. The results of this study are in accordance with the WRIST and BETA-WRIST data. After 6 months both studies revealed an ISR-free survival rate of 86% (WRIST) and 66% (BETA-WRIST), respectively. The ISR rates in the own control group (70%) were comparable to the placebo groups in WRIST (68%) and BETA-WRIST (72%). Interestingly, patients with more than three ISRs before ICBT had the lowest ISR rate after ICBT.

Clinical applications of 188Re-labelled radiopharmaceuticals for radionuclide therapy

188Re is a radionuclide in which there is widespread interest for therapeutic purposes because of its favourable physical characteristics. Moreover, it can be eluted from an on-site installable 188W/188Re generator, which has a useful shelf-life of several months. Most of the clinical experiences gained with 188Re concern the use of 188Re-1,1-hydroxyethylidenediphosphonate (188Re-HEDP) for bone pain palliation in patients suffering prostate cancer. The maximum tolerated activity was 3.3 GBq 188Re-HEDP and if the platelet count exceeded 200 x 10(9) l(-1), the administration of 4.4 GBq appeared safe. Evidence for repeated administrations of 188Re-HEDP rather than single injections was established. In general, pain palliation occurs in 60-92% of patients with only moderate transient toxicity, mainly related to changes in blood counts. Also in haematology, radioimmunotherapy by means of 188Re might play a role by selectively targeting the bone marrow in patients undergoing conditioning prior to haematopoetic stem cell transplantation. The feasibility of such an approach was proven using a Re-labelled monoclonal antibody directed toward the CD66-antigen. More recently, encouraging safety data on locoregional treatment of primary liver tumours using 188Re-labelled lipiodol were reported. The normal organs at greatest risk for toxicity are the normal liver and the lungs. About 50% of the patients reported mild and transient side effects, mainly consisting of low grade fever, right hypochondrial discomfort or aggravation of pre-existing liver impairment. Besides the applications in oncology 188Re-based therapies have also been pioneered for benign condition such as prevention of re-stenosis following angioplasty and for radiosynovectomy in cases of refractory arthritis.

Three-year follow-up after intracoronary beta-radiation therapy for in-stent restenosis

BACKGROUND

Most studies that proved intracoronary radiation therapy (IRT) to be highly effective to reduce recurrent restenosis after treatment of in-stent restenosis (ISR) have looked at time periods up to 12 months. Whether the beneficial effect from radiation is sustained during long-term follow-up remains a concern. This study sought to evaluate the effectiveness of IRT using a beta-emitter during a 3-year follow-up period.

METHODS

One hundred twenty-eight consecutive symptomatic patients (mean age, 63 +/- 11 years) with 134 in-stent restenotic lesions were treated for ISR with IRT (noncentred beta-emitter, Novoste; radiation dosis 21.1 +/- 3.1 Gy). Six-month angiographic follow-up was obtained in 104 patients (81%) with 105 lesions (78%). All patients underwent 36-month clinical follow-up.

RESULTS

Six-month angiographic restenosis rate was 22% in stent (29% in lesion) with an in-stent late loss of 0.49 +/- 0.62 mm. Target lesion resvascularization (TLR) at 6-month follow-up was performed in 23 cases (18%). MACE (death, myocardial infarction, and target vessel revascularisation) was observed in 24 patients (19%). At 36-month follow-up, TLR increased to 36 cases (28%) and MACE was observed in 47 patients (37%). In a multivariate analysis, minimal lumen diameter before treatment of ISR using IRT was the only predictor of recurrent TLR at 36 months (OR = 0.131; 95% CI, 0.068-0.254; p = 0.002). In a subgroup of patients (N = 15) without restenosis at 6-month angiography but with clinically driven recurrent late angiography (mean, 18 +/- 7 months); in-lesion late loss increased from 0.47 +/- 0.54 mm at 6 months to 1.27 +/- 0.76 mm at repeated angiography (p = 0.005).

CONCLUSION

There is a considerable number of delayed recurrent restenosis post IRT for ISR. This is due to ongoing late loss more than 6-month post IRT. The minimal lumen diameter before IRT predicts the need for recurrent TLR at 36 months.

Gadolinium neutron capture brachytherapy (GdNCB), a new treatment method for intravascular brachytherapy

Restenosis is a major problem after balloon angioplasty and stent implantation. The aim of this study is to introduce gadolinium neutron capture brachytherapy (GdNCB) as a suitable modality for treatment of stenosis. The utility of GdNCB in intravascular brachytherapy (IVBT) of stent stenosis is investigated by using the GEANT4 and MCNP4B Monte Carlo radiation transport codes. To study capture rate, Kerma, absorbed dose and absorbed dose rate around a Gd-containing stent activated with neutrons, a 30 mm long, 5 mm diameter gadolinium foil is chosen. The input data is a neutron spectrum used for clinical neutron capture therapy in Studsvik, Sweden. Thermal neutron capture in gadolinium yields a spectrum of high-energy gamma photons, which due to the build-up effect gives an almost flat dose delivery pattern to the first 4 mm around the stent. The absorbed dose rate is 1.33 Gy/min, 0.25 mm from the stent surface while the dose to normal tissue is in order of 0.22 Gy/min, i.e., a factor of 6 lower. To spare normal tissue further fractionation of the dose is also possible. The capture rate is relatively high at both ends of the foil. The dose distribution from gamma and charge particle radiation at the edges and inside the stent contributes to a nonuniform dose distribution. This will lead to higher doses to the surrounding tissue and may prevent stent edge and in-stent restenosis. The position of the stent can be verified and corrected by the treatment plan prior to activation. Activation of the stent by an external neutron field can be performed days after catherization when the target cells start to proliferate and can be expected to be more radiation sensitive. Another advantage of the nonradioactive gadolinium stent is the possibility to avoid radiation hazard to personnel.

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.

Different responses by cultured aortic and venous smooth muscle cells to gamma radiation

BACKGROUND

Stenosis of hemodialysis arteriovenous grafts is usually focal and caused by the proliferation of vascular smooth muscle cells (SMCs). External radiation of the graft is a potential strategy to prevent stenosis; however, the relative responsiveness of arterial and venous SMCs to radiation is unknown.

METHODS

Human aortic and saphenous vein SMCs were cultured in a medium containing growth factors and serum and treated with 0 to 50 Gy in a gamma irradiator. At 2 to 20 days post-irradiation, cell counting, methylthiazoletetrazolium dye reduction, [(3)H]-thymidine uptake, and bromodeoxyuridine (BrdU) incorporation assays were performed.

RESULTS

All assays showed that 1 to 50 Gy inhibited the proliferation of both aortic and venous SMCs in a dose-dependent manner. Importantly, venous cells were less susceptible to radiation in all assays, compared to aortic cells. At day 10, 1 to 50 Gy of radiation inhibited the increase in the number of aortic cells by 24% to 66% and venous cells by 8% to 25% (P < 0.01) (aortic vs. venous). The differences between aortic and venous cells varied among different assays and were most pronounced in the BrdU assay.

CONCLUSION

Inasmuch as myointimal hyperplasia occurs at both arterial and venous anastomoses, future strategies using radiation to prevent hemodialysis vascular access stenosis should take these differences into consideration.

Vascular Brachytherapy with192Ir after Femoropopliteal Stent Implantation in High-Risk Patients: Twelve-month Follow-up Results from the Vienna-5 Trial

PURPOSE

To prospectively evaluate the effectiveness of endovascular brachytherapy in the prevention of restenosis after femoropopliteal stent implantation in high-risk patients.

MATERIALS AND METHODS

Patients provided written informed consent to participate in this study, which was approved by the ethics committee. A total of 88 patients (mean age, 67.7 years +/- 10.1; 57 men [65%], 31 women [35%]) with femoropopliteal lesions (mean treatment length, 16.8 cm +/- 7.3) were included. Patients underwent percutaneous transluminal angioplasty (PTA) and stent implantation and were randomized in a double-blind fashion to undergo either gamma brachytherapy with an iridium 192 source or treatment with nonradioactive seeds. A 14-Gy dose of iridium 192 was prescribed at 2 mm into the arterial wall (target depth equals vessel radius plus 2 mm). The primary end point of the study was angiographic binary restenosis of more than 50% at 6-month follow-up. Secondary end point was either percutaneous or surgical target lesion revascularization after 6 months. Continuous data are presented as mean +/- standard deviation. Categorical data are expressed as percentages. Student t test was used to compare continuous data; chi(2) test was used to compare categorical values. Survival function was calculated with the Kaplan-Meier method. Multivariate Cox proportional hazard regression analysis was performed to enable evaluation of multivariate predictors of recurrence at 6- and 12-month follow-up. Variables included brachytherapy, clinical stage, lesion length, de novo and recurrent lesion, vessel run off, prior stenosis or occlusion, diabetes mellitus, and stent model.

RESULTS

Revascularization and brachytherapy were accomplished successfully in all patients. The overall 6-month recurrence rate was 35% in patients who underwent only stent implantation and 33% in patients who underwent both stent implantation and brachytherapy (P = .89). Nine (10%) patients developed early reocclusion in the segment treated with a stent (two patients [4%] in the stent group and seven [17%] in the stent and brachytherapy group); of these patients, three in the stent and brachytherapy group experienced reocclusion within 24 hours of the intervention. Late (>30 days after intervention) thrombotic occlusion was observed in three patients (7%) in the stent and brachytherapy group.

CONCLUSION

Brachytherapy does not improve 6-month patency after femoropopliteal stent implantation in high-risk patients because of a high incidence of early and late thrombotic occlusion.

Three-year follow-up after intravascular γ-radiation for in-stent restenosis in saphenous vein grafts

The Washington Radiation for In-Stent Restenosis Trial in Saphenous Vein Grafts (SVG WRIST) demonstrated safety and efficacy of intravascular radiation therapy (IRT) for the treatment of in-stent restenosis (ISR) in SVG at 12 months. In this study, we aimed to examine whether the safety and efficacy of IRT is durable up to 36 months. One hundred twenty patients with diffuse ISR in SVG underwent balloon angioplasty, laser or atherectomy ablation, and/or additional stenting. After successful intervention, patients were randomly assigned in a double-blind fashion to intravascular treatment with a ribbon containing either iridium (Ir)-192 (n = 60) or nonradioactive seeds (n = 60). The prescribed dose at 2 mm from the source was either 14 or 15 Gy in vessels 2.5-4.0 mm or 18 Gy in vessels > 4.0 mm in diameter. At 36 months, target lesion revascularization (TLR; 43% vs. 66%; P = 0.02) and target lesion revascularization-major adverse cardiac event (TLR-MACE; 49% vs. 71%; P = 0.02) rates continued to be lower in the IRT group, but both target vessel revascularization (TVR; 59% vs. 71%; P = 0.17) and TVR-MACE (63% vs. 77%; P = 0.11) rates were not. In SVG WRIST, patients with ISR treated with IRT had a marked reduction in the need for repeat TLR at 36 months, with sustained clinical benefit at 3 years despite late recurrences, which were more pronounced in the radiation group.

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

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.

Centered endovascular irradiation to prevent postangioplasty restenosis of arteriovenous fistula in hemodialysis patients; Results of a feasibility study

PURPOSE

To report follow-up results of a prospective trial on centered endovascular gamma-irradiation (CEGI) after percutaneous transluminal angioplasty (PTA) for stenosis of arteriovenous fistula in hemodialysis patients.

METHODS AND MATERIALS

Eight patients receiving PTA for recurrent (n = 4) or de novo arteriovenous fistula stenoses were treated with CEGI with iridium-192 (14 Gy). Angiography was performed after 6 and 12 months or if problems reoccurred during hemodialysis. Parameters of hemodialysis and duplex sonography were determined the day before and after PTA and after 1, 3, 6, 9, and 12 months.

RESULTS

CEGI was performed successfully and without complications in seven patients. In six patients, restenosis occurred 6-52 weeks (mean 20.8 +/- 17.9 weeks) after PTA and required PTA. Parameters of hemodialysis and duplex sonography deteriorated during follow-up.

CONCLUSIONS

Centered endovascular gamma-irradiation with iridium 192 immediately after PTA of fistula stenoses was a safe and feasible method but did not prevent restenosis.

Endovascular brachytherapy prevents restenosis after femoropopliteal angioplasty: results of the Vienna-3 randomised multicenter study

BACKGROUND AND PURPOSE

The aim of the trial was to investigate the effect of Iridium-192 gamma endovascular brachytherapy on reduction of restenosis after femoropopliteal angioplasty.

PATIENTS AND METHODS

Between Oct, 1998 and Jul, 2001 a total of 134 patients have been randomized after successful angioplasty to brachytherapy or sham irradiation in a prospective, randomized, multicenter, double blind controlled trial. Patients with de novo lesion of at least 5 cm or recurrent lesion of any length after prior angioplasty have been enrolled. Brachytherapy was performed with 7F centering catheter. Mean lesion length was 9.1cm (1.5-25 cm) and mean intervention length 13.6 cm (4-27.5 cm) in brachytherapy cohort.

RESULTS

In placebo cohort mean lesion length was 10.3 cm (2-25 cm) and mean intervention length 14.1 cm (2-29 cm). A dose of 18 Gy was prescribed 2 mm from the surface of centering balloons. Analyzed (based on angiography) on intention to treat basis the binary restenosis rate at 12 months was 41.7% (28/67) in brachytherapy cohort and 67.1% (45/67) in placebo cohort (chi2 test, P<0.05). Corresponding data for as treated analysis (A total of 38 patients was excluded from analysis due to lack of follow-up, early recurrence within 30 days and >30% residual stenosis after angioplasty) have been 23.4% in the brachytherapy and 53.3% in the placebo group (P<0.05), respectively. The cumulative patency rates after 24 months on intention to treat analysis were 54% in the brachytherapy and 27% in the placebo group (P<0.005). Corresponding data for as treated analysis were 77% in the brachytherapy and 39% in the placebo group (P<0.001). Late thrombosis was not seen.

CONCLUSIONS

Significant reduction of restenosis rate was obtained with endovascular gamma brachytherapy after femoropopliteal angioplasty.

Effective dose for patients undergoing coronary and femoral intravascular radiotherapy involving an HDR 192Ir source

Effective dose equivalent (EDE), and effective dose (ED) for coronary and femoral Intravascular brachytherapy (IVBT) procedures involving a 370 GBq (10 Ci) HDR 192Ir gamma source are tabulated. MIRD stylised models and the MCNP Monte Carlo code were used for the calculations. For coronary irradiation, the normalised EDE is 0.18 mSv (GBq min)(-1) and the ED is 0.056 mSv (GBq min)(-1). For femoral IVBT, the normalised EDE is 0.01629 mSv (GBq min)(-1) and the ED is 0.01195 mSv (GBq min)(-1). Although the medical benefits to a patient undergoing IVBT are often significant and justified, patient doses are high compared with dose limits for radiation protection purposes. As IVBT is becoming a routine procedure, data in this paper could be useful to manage the procedures efficiently.

External beam radiation therapy reduces the rate of re-stenosis in patients treated with femoral stenting: results of a randomised study

BACKGROUND AND PURPOSE

To evaluate the feasibility and efficacy of external beam irradiation (EBI) for the prevention of re-stenosis due to neointimal hyperplasia, after percutaneous transluminal angioplasty (PTA) and stent placement of the superficial femoral artery.

PATIENTS AND METHODS

A total of 60 patients with the diagnosis of superficial femoral artery stenoses or occlusions due to peripheral arterial obstructive disease underwent PTA and implantation of a self-expandable stent at their superficial femoral artery. After the procedure, patients were randomised and 30 of them received EBI (6 MV photons, total dose 24 Gy in six fractions in 2 weeks), while the rest 30 received no radiation therapy.

RESULTS

EBI was technically feasible in all patients, without serious radiation related side effects. Overall, a statistically significant difference was observed in stenosis categories between the two groups at 6 months follow-up (P=0.04). More specifically, significantly more patients in the control group presented with stenosis greater or equal than 70% [EBI group 30% (9/30); control group 66.7% (20/30); P=0.009]. This difference in the percentage of re-stenosis had as a consequence significantly lower re-intervention rates among the patients of the irradiated group [17% (5/30) versus 47% (14/30); P=0.025] during the 6 months follow-up period. We also observed that the irradiated patients had re-stenosis at the stent ends, while the non-irradiated had re-stenosis at the stent ends and the lumen. Three of the irradiated patients, who discontinued the anti-platelet treatment, have shown thrombosis of the irradiated artery during the first month from the completion of the treatment.

CONCLUSIONS

It is our belief that EBI is a feasible, safe and effective method for the prevention of neointimal hyperplasia at the superficial femoral artery. Further studies are deemed necessary to optimise the radiotherapy schedule.

Dosimetric consequences of manual pullback procedure for coronary artery radiotherapy with 90Sr/90Y beta-source

PURPOSE

This work presents a quantitative dosimetric analysis of the Novoste (90)Sr/(90)Y beta-source cardiovascular brachytherapy treatments using a manual pullback technique for patients with in-stent restenosis.

METHODS AND MATERIALS

Based on our previous measurements, a model was developed to estimate the dose in the middle of the junction region for tandem irradiation expressed as fraction of prescription dose (FPD) and dosimetric overlap length (DOL) receiving more/less than a threshold dose. The overlap/gap size was measured using the digital cine images recorded during treatment and then FPD and DOL were quantified.

RESULTS

Statistical analysis of 55 patients showed that the overlap size and the FPD at 2 mm radial distance were in range of 0 to 23 mm and 13-200% of prescription dose (Rx), respectively. Four gaps out of 76 pullback cases were found, but their size was at most 5 mm.

CONCLUSION

Use of a 5 mm overlap avoided underdosed regions in the vast majority of the cases. These results are the first step towards an analysis of the clinical outcome of these patients.

EPR study of radiation stability of organic plastic scintillator for cardiovascular brachytherapy Sr90-Y90 beta dosimetry

Nowadays, more than one million percutaneous transluminal coronary angioplasties are being performed annually throughout the world. Restenosis is a significant problem associated with these angioplasty procedures. Radiation treatment with catheter-based beta-emitter sources is currently under clinical trial to prevent this problem. Due to fast and worldwide introduction of beta-sources for intravascular application, there is a growing interest in the dosimetry aspects. However, accurate dosimetry of beta-radiation is more difficult than that of gamma-radiation. Suitable detectors are not yet available with accuracy down to a tenth of a millimeter. Conventional measuring systems are not capable of such spatial resolution, except radiochromic film. However, film dosimeters have limited sensitivity and their radiation characteristics are different than those of tissue; therefore dose measurements require corrections. An alternative is to use water-equivalent plastic scintillators. In this work, organic plastic scintillator (BCF-10) dosimetry is studied using the Monte Carlo (MC) technique PENELOPE, and its radiation stability, after irradiation, is experimentally studied through electron paramagnetic resonance (EPR). Depth dose and dose profile are measured and compared to film dosimetry results. The EPR technique shows that the recovery time is dose independent in this kind of fiber and shows good stability.

Intracoronary brachytherapy following drug-eluting stent failure. It's still not time to hang up the spikes!

Drug-eluting stents (DES) have significantly reduced the incidence of restenosis. Although the results obtained with these novel antiproliferative devices are encouraging, recent reports have shown that DES are not completely immune from restenosis. Therefore, the broad use of DES has inevitably led to a major issue: treatment of DES failure. Intracoronary brachytherapy (IBT) represents an important advancement for treatment of in-stent restenosis (ISR) and has led to important pathophysiological insight on the restenotic process. To date, IBT, when properly used, still represents the gold standard for treatment of ISR. However, experience with IBT is for treatment of ISR occurring with bare metal stents (BMS). Whether IBT may be used with the same safety and efficacy profile as an adjunctive treatment for ISR following DES implantation is still unknown. In this article, we report the outcome of a series of patients with DES failure treated with IBT. IBT for treatment of DES failure was shown to be both safe and efficient and, therefore, until ISR exists, IBT still remains an important player in this growing and even more challenging setting.

The availability of contrast media in the application of Holmium-166-DTPA for vascular brachytherapy

Since coronary angioplasty using a liquid radiation source is performed with computed tomography(CT) angiography, use of a CT contrast agent is a good alternative to see if the balloon has close contact with the blood vessel wall for the delivery of a sufficient radiation dose to the stenotic artery. In order to examine the usefulness of the CT contrast agent as a diluent of a liquid radiation source, various physicochemical studies and in vivo stability studies using animals were implemented using (166)Ho-DTPA for vascular brachytherapy and a PTCA balloon catheter. For this study, three CT contrast agents, Hexabrix (320)(Rx), Iomeron (350)(Rx) and Visipaque (320)(Rx) were used. Results showed that (166)Ho radiolabeled component of Hexabrix (320)(Rx) and the (166)Ho-complex was proposed to be (166)Ho-EDTA. However, in the case of Iomeron (350)(Rx) and Visipaque (320)(Rx), no other (166)Ho-complex was formed except the desired (166)Ho-DTPA. In the case where (166)Ho-EDTA (>98% radiolabeling yield) was administrated to rabbits, only 10% of the administered dose was excreted through the urinary track 30 min after injection. However, in the animal experiment where Hexabrix (320)(Rx) was added to the (166)Ho-DTPA vial with the volume ratio of 1:1, over 80% of the administrated dose accumulated into the bladder within 30 min after injection. Therefore, Hexabrix (320)(Rx) is applicable when it is used as a diluent of a (166)Ho-based liquid radiation source and its volume is applied in a minimal manner to visualize the balloon catheter. In conclusion, the use of a CT contrast agent in the clinical application of a liquid radiation source has beneficiary effects such as visualization of both the position and shape of the balloon are possible and most importantly, whether or not there is a formation of a void volume of liquid inside the balloon as well as the detection of radiation leakage on a real-time basis, on site during the angioplasty.

Radionuclides-hyaluronan-conjugate thromboresistant coatings to prevent in-stent restenosis

Catheter-based brachytherapy is one of the most effective modalities to inhibit hyperplasia following revascularization procedures. Radioactive stents have failed, however, to prevent clinical hyperplasia due to excessive late lumen loss on the edge of the devices. Numerous strategies have been proposed to circumvent the drawbacks of irradiation therapies, such as the use of more appropriate radionuclides or the "hot-end" stents approach. This paper describes versatile radioactive devices obtained by coating plasma functionalized surfaces-stents or catheters-with a hyaluronan (HA)-diethylenetriamine pentaacetic acid (DTPA) conjugate (HA-DTPA) complexed with a gamma or beta radionuclide. Yttrium and indium were used as radionuclide models, due to their suitability for endovascular radiotherapy. X-ray photoelectron microscopy and time-of-flight secondary ions mass spectrometry analyses confirmed the successful immobilization of the HA-DTPA conjugate on both the metallic (NiTi) and polymeric (Teflon) plasma functionalized surfaces. HA-DTPA-coated surfaces were significantly more hydrophilic than bare surfaces (39.5 degrees vs. 67 degrees on NiTi substrate and 29 degrees vs. 128 degrees on Teflon substrate). Therapeutic doses of yttrium and indium were easily loaded onto the surfaces and remained stable over 2 weeks with a radionuclide loss of about 6%. The HA-DTPA-coated Teflon surfaces presented significantly less fibrinogen adsorption than uncoated materials in an in vitro flow model. This approach, which combines the hemocompatibility of HA-coated surfaces and the anti-proliferative effects of an appropriate radiotherapy, constitutes a promising methodology to alleviate the restenosis induced by existing devices.

The role of brachytherapy and Cutting BalloonTM angioplasty in the current treatment of stent restenosis

The Gamma I, START and INHIBIT trials conclusively demonstrate the feasibility, safety and efficacy of intracoronary radiation as the treatment of choice for stent restenosis. Further reports confirm this finding and extend the indications. Vascular brachytherapy should be made available for all patients with diffuse stent restenosis. Specific devices such as cutting balloons may improve the procedure but does not seem to have an impact alone on the evolution.

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.

Evolution of angiographic restenosis rate and late lumen loss after intracoronary beta radiation for in-stent restenotic lesions

The aim of this study was to investigate the time course of angiographic restenosis rate and late loss after successful percutaneous coronary intervention and vascular brachytherapy with beta-irradiation using strontium-90/yttrium-90 in 98 patients who were prospectively enrolled into a quantitative angiographic and clinical follow-up protocol at 6, 12, and 24 months after the index procedure, regardless of their symptom status. Actuarial restenosis rates measured 11.2 +/- 5% at 6 months of follow-up, 24.5 +/- 5% at 12 months, and 28.5 +/- 6% at 24 months, respectively. Late loss of the stent segment during the first 6 months measured 0.38 +/- 0.40 mm (6 to 12 months: 0.25 +/- 0.38 mm; 12 to 24 months: 0.16 +/- 0.32 mm), of the injured segment 0.27 +/- 0.21 mm (6 to 12 months: 0.21 +/- 0.26 mm; 12 to 24 months: 0.13 +/- 0.24 mm), of the irradiated segment 0.18 +/- 0.29 mm (6 to 12 months: 0.19 +/- 0.31 mm; 12 to 24 months: 0.11 +/- 0.27 mm), and of the analysis segment 0.18 +/- 0.36 mm (6 to 12 months: 0.17 +/- 0.29 mm; 12 to 24 months: 0.11 +/- 0.20 mm). Restenosis after angioplasty and beta-irradiation of in-stent restenotic lesions is not complete within 6 months but is sustained with a gradual decrease over 24 months.

Coronary in-stent restenosis following beta brachytherapy A histopathological examination

Two cases of in-stent restenosis of a coronary artery bypass vein graft following beta (beta) brachytheraphy are presented. Previously unreported histopathology of directed atherectomy specimens of such restenotic lesions and a discussion of their proposed significance form the basis of this report.

Adventitial response to intravascular brachytherapy in a rabbit model of restenosis

BACKGROUND

The incidence of late major adverse cardiac events (MACE) after coronary brachytherapy is higher than in controls. Because expansive remodeling has been shown to correlate with poor clinical outcome after vascular interventions, we studied adventitial changes after intravascular irradiation in a rabbit model.

METHODS

Twenty normolipidemic rabbits underwent balloon injury in both external iliac arteries. One artery was assigned for subsequent irradiation with a 90Y source (15 Gy or 30 Gy at 0.5 mm in the vessel wall). After four weeks morphometric measurements were made and cell density and collagen amount determined. Staining for Ki67 identified proliferating cells; apoptotic cells were identified by TUNEL staining. Proliferative and apoptotic indices were calculated as the number of respective positive cells/total cell count x100.

RESULTS

The neointimal area decreased to 0.27 +/- 0.3 mm2 after irradiation compared with 0.55 +/- 0.2 mm2 in controls (p=0.007), whereas adventitial area increased from 0.62 +/- 0.3 mm2 to 0.87 +/- 0.3 mm2 (p=0.02). Irradiation reduced both the proliferative (0.95 +/- 2.6 vs. 3.73 +/- 4.7, p=0.026) and apoptotic (0.006 +/- 0.02 vs. 0.107 +/- 0.2, p=0.03) indices in the neointima, but not in the other arterial-wall layers. Collagen amount and arterial remodeling did not differ between the groups. There was no difference between 15 and 30 Gy in any of the parameters, although adventitial thickening was more pronounced in the high-dose group.

CONCLUSIONS

In normolipidemic rabbits, intravascular beta-irradiation after balloon angioplasty is associated with an increase in neoadventitia and a reduction of neointima. It is conceivable that this phenomenon may contribute to the increased incidence of late MACE after vascular brachytherapy.

Usefulness of periprocedural creatinine phosphokinase-MB release to predict adverse outcomes after intracoronary radiation therapy for in-stent restenosis

We aimed to analyze periprocedural creatinine phosphokinase (CPK)-MB elevation in patients treated with intracoronary radiation therapy (IRT) for in-stent restenosis (ISR) to risk stratify these patients. The clinical significance of periprocedural CPK-MB elevation after IRT for ISR is unknown. An elevated CPK-MB has been associated with increased mortality after conventional angioplasty. We evaluated 1,326 patients who were enrolled in radiation trials for ISR at the Washington Hospital Center using gamma- and beta-emitters. Patients were analyzed according to degree of CPK-MB increase within 24 hours of the index IRT procedure (normal CPK-MB, CPK-MB 1 to 3 times the upper limit of normal, or CPK-MB >3 times the upper limit of normal). Patients with CPK-MB >3 times the upper limit of normal were older (64 +/- 12 years, p = 0.04), more likely to be smokers (64%, p = 0.04), hypertensive (85%, p <0.01), and diabetic (49%, p = 0.04). The cohort with the highest CPK-MB release (CPK-MB >3 times the upper limit of normal) had significantly higher rates of adverse clinical events at 12 months (major adverse cardiac events 40%, p <0.01), including death (9.3%, p <0.01) and late thrombosis (6.3%, p <0.01). Periprocedural CPK-MB elevation is of prognostic importance in patients treated with IRT for ISR, and its analysis appears to be mandatory to risk stratify these patients. The impact of glycoprotein IIb/IIIa antagonists in reducing periprocedural CPK-MB release awaits evaluation.

Treatment of in-stent restenosis for saphenous vein grafts using intravascular brachytherapy: regulatory challenges and clinical application

Treatment of in-stent restenosis using intravascular brachytherapy (IVBT) has been demonstrated to be successful and has become the standard of care for native coronary artery disease. Based on the current Food and Drug Administration (FDA) indications for use and the clinical demand to increase the scope of this form of therapy to include saphenous vein grafts for the Beta-Cath System (Novoste Corporation, Norcross, Georgia), we set out to obtain institutional approval for off-label use. Identification of institutional regulatory bodies and related procedures for obtaining off-label device use was performed. Additionally, the IVBT written directive proscription and patient informed consent forms were revised to accurately administer radiation dose and to disclose the regulatory status of using IVBT for this anatomic site. While the specifics are outlined in this report, this process and the resources needed to obtain institutional approval for off-label use are indicative of that to be expected at similar institutions.

[Invasive cardiology--focus on restenosis. Part I]

In-stent restenosis is mainly caused by neointima proliferation and represents a pathological process which histology is different from that of restenosis after balloon angioplasty. Frequency of in-stent restenoses increases parallel with progressively increasing number of procedures of coronary stenting. The review summarizes results of research devoted to restenosis pathology and pathogenesis including animal studies, presents methods of mechanical treatment of in-stent restenoses (balloon inflation, direct and rotational atherectomy), as well as techniques of beta and gamma irradiation aimed at prevention of restenosis development.

Post-Dilatation Intravascular Brachytherapy Trials on Hypercholesterolemic Rabbits Using 32P-Phosphate Solutions in Angioplasty Balloons

PURPOSE

Response of peripheral arteries to post-dilatation intravascular brachytherapy (IVBT) using 32P liquid sources was studied in a rabbit model.

METHODS

The applied sources were angioplasty balloons filled with aqueous solutions of Na2H32PO4, NaCl and iodinated contrast. Dose distribution was calibrated by thermoluminescence dosimetry. The uncertainty of in vitro determinations of the activity-dose dependence was +/- 15-30%. The animal experiments were performed on rabbits with induced hypercholesterolemia. The 32P sources were introduced into a randomly chosen (left or right) iliac artery, immediately after balloon injury. Due to the low specific activity of the applied sources, the estimated 7-49 Gy doses on the internal artery surface required 30-100 min irradiations. A symmetric, balloon-occluded but non-irradiated artery of the same animal served as control. Radiation effects were evaluated by comparing the thicknesses of various components of irradiated versus untreated artery walls of each animal.

RESULTS

The treatment was well tolerated by the animals. The effects of various dose ranges could be distinguished although differences in individual biological reactions were large. Only the 49 Gy dose at "zero" distance (16 Gy at 1.0 mm from the balloon surface) reduced hypertrophy in every active layer of the artery wall. The cross-sectional intimal thicknesses after 7, 12, 38 and 49 Gy doses were 0.277, 0.219, 0.357 and 0.196 mm2 respectively, versus 0.114, 0.155, 0.421 and 0.256 mm2 in controls (p < 0.05). The lowest radiation dose on the intima induced the opposite effect. Edge intimal hyperplasia was not avoided, which agrees with other reports. The edge restenosis and the variability of individual response to identical treatment conditions must be considered as limitations of the post-dilatation IVBT method.

CONCLUSION

Only application of highest irradiation doses was effective. The irradiation dose should be planned and calculated for adventitia.

Usefulness of the angiographic pattern of in-stent restenosis in predicting the success of gamma vascular brachytherapy

The prognostic role of the angiographic pattern of in-stent restenosis after gamma vascular brachytherapy was assessed from a pooled data set of 4 clinical trials comprising 295 irradiated patients with matched baseline and follow-up angiograms. The binary angiographic restenosis rate increased with worsening in-stent restenosis patterns; however, target lesion revascularization and major adverse cardiac event rates increased for focal, diffuse, and proliferative patterns of in-stent restenosis but not for total occlusions.

Beta brachytherapy of an old degenerated saphenous vein graft with occlusive in-stent restenosis

We report a case of obstructive in-stent restenosis in a diffusely diseased saphenous vein graft complicated by a non-ST-elevation myocardial infarction. With tirofiban infusion, the extensively occluded saphenous bypass was reperfused, establishing a TIMI flow 3, and then entirely irradiated with a beta source (32P) without any complication. At 7 months the patient was asymptomatic and the control angiogram did not reveal any restenosis. In conclusion, 32P beta brachytherapy may be extremely effective not only in case of native vessel in-stent restenosis but also in cases of high-risk vein graft in-stent restenosis.

Deposition of (90)YPO(4) and (144)CePO(4) radioisotopes on polymer surfaces for radiation delivery devices

Intravascular irradiation with beta emitters inhibits restenosis in arteries after balloon angioplasty or stent implantation. Yttrium-90 ((90)Y, T(1/2)=64 h) and cerium-144 ((144)Ce, T(1/2)=286 d) emit beta particles (E(max)=2.28--3.50 MeV) having an ideal energy range for brachytherapy delivery system. In this article, a previously reported method for depositing (32)P on poly(ethylene terephtalate) (PET) surfaces is generalized and modifications that allow deposition of other beta-emitting radioisotopes, such as (90)Y and (144)Ce, are demonstrated. PET films were first coated with chitosan hydrogel and then adsorbed different amounts of phosphoric acid (PA) in aqueous solutions. Yttrium was deposited onto the surface as YPO(4) after the films were immersed in YCl(3) solutions. 1 muCi (90)YCl(3) (2 x 10(-9) g) was used in each sample as a tracer for measuring the deposition efficiency, which is defined as the percentage of YCl(3) deposited on the surface compared to the amount of YCl(3) in solutions before the deposition. In order to improve the safety of brachytherapy treatments, polyurethanes were used to seal the deposited radioisotopes on the surface to minimize the leakage of the isotopes into the patients. The generality of this method presented here for a wide variety of particular radioisotopic components allows design of a broad range of versatile radioisotope sources.

Usefulness of beta radiation for de novo and in-stent restenotic lesions in saphenous vein grafts

Following successful angioplasty of 49 saphenous vein graft lesions, a novel, self-centering phosphorus-32 solid foil beta source encapsulated within a dual-balloon membrane was used to deliver 20 Gy 1 mm into the vessel wall. Clinical and angiographic recurrence rates at 12 months were low, especially in de novo lesions.

External beam radiation for prevention of intimal hyperplasia in peripheral arterial bypasses

PURPOSE

Neointimal hyperplasia is one of the limiting factors in infrainguinal prosthetic vascular grafting. We conducted a pilot study to assess the possible role of radiotherapy for the prevention of this proliferating cellular process.

METHODS AND MATERIALS

Ten patients (7 men, 3 women; median age: 73 years) suffering from critical leg ischemia were treated by infrainguinal revascularization using 6-mm polytetrafluoroethylene. Postoperative radiation therapy of the anastomotic sites started within 24 h. A dose of 20.4 Gy was delivered in 12 fractions in 2.5 weeks by external beam radiation with electrons. The target volume was defined as the clip-marked anastomotic region plus a 1.5-cm safety margin in each direction.

RESULTS

Radiation therapy was technically feasible in all cases without radiation-related side effects. In one patient, radiotherapy had to be terminated prematurely, because of a hematoma at the distal anastomotic site with consequent skin necrosis. One patient developed an occlusion of a suprainguinal graft without anastomotic stenosis after 9 months; 2 other grafts occluded at 12-month intervals. At a median follow-up of 16 months, the remaining 6 patients had no signs of restenosis.

CONCLUSIONS

The restenosis rate of peripheral vascular grafts after external beam radiation was lower than expected without additional treatment. The value of this approach will now be determined in a randomized prospective trial.

Could X-ray microbeams inhibit angioplasty-induced restenosis in the rat carotid artery?

BACKGROUND

Parallel, thin (<100 microm) planes of synchrotron-generated X rays, have been shown to spare normal tissues and preferentially damage tumors in animal models. The aim of the present study was to assess the effect of such microbeams directed unidirectionally on angioplasted rat carotid arteries.

METHODS AND MATERIALS

Three groups of Sprague-Dawley rats were studied: (a) rats with normal, untreated arteries, (b) rats treated by balloon angioplasty, but not irradiated, and (c) rats treated with balloon angioplasty and exposed to single fraction, unidirectional, parallel, microbeams an hour after angioplasty. The microbeam array, 15 mm widex7.6 mm high, consisting of 27-microm-wide beam slices, spaced 200 microm center-to-center laterally traversed the damaged artery. The in-depth in-beam dose was 150 Gy, the "valley" dose (dose midway between microbeams resulting mainly from X-ray scattering) was 4.5 Gy on average, and the "integrated" (averaged) dose was 26 Gy.

RESULTS

Microbeam irradiation, as given in the present study, was tolerated, but was insufficient to significantly suppress the neointimal hyperplasia.

DISCUSSION

The microbeam dose used is considered low. Dose escalation would be necessary to reach conclusive results regarding the X-ray microbeam efficacy to control restenosis.

Endovascular brachytherapy for treatment of bilateral renal artery in-stent restenosis

Percutaneous transluminal angioplasty of renal artery stenosis is an attractive alternative to surgical therapy. However, even with endovascular stenting, the overall rate of restenosis is 21%. While brachytherapy for coronary in-stent restenosis has proven efficacy, its use for renal artery in-stent restenosis has not been formally evaluated. We report a case of bilateral in-stent renal artery restenosis treated with endovascular brachytherapy.

Clinical and angiographic acute and follow up results of intracoronary beta brachytherapy in saphenous vein bypass grafts: a subgroup analysis of the multicentre European registry of intraluminal coronary beta brachytherapy (RENO)

OBJECTIVE

To assess clinically and angiographically the feasibility, safety, and effectiveness of vascular brachytherapy (VBT) in saphenous vein bypass grafts (SVG).

PATIENTS AND METHODS

67 of 1098 (6.1%) consecutive patients of the European registry of intraluminal coronary beta brachytherapy underwent treatment for 68 SVG lesions by VBT using a Sr/Y(90) source train (BetaCath). Clinical follow up data were obtained for all of them after a mean (SD) of 6.3 (2.4) months and angiographic follow up was performed in 61 patients (91.0%) after 6.9 (2.0) months.

RESULTS

58 (86.6%) patients were men, their mean (SD) age was 66 (10) years, 28 (41.8%) had unstable angina, and 21 (31.3%) had diabetes. Fifty three (77.9%) lesions were in-stent restenosis, 13 (19.1%) de novo lesions, and 2 (3.0%) non-stented restenotic lesions. Mean (SD) reference diameter before the intervention was 4.19 (0.52) mm, mean (SD) lesion length was 23.56 (20.38) mm, and mean (SD) minimum lumen diameter measured 0.73 (0.62) mm. Mean (SD) acute gain was 3.02 (0.88) mm. The prescribed radiation dose was 20.1 (3.2) Gy. Pullback manoeuvres were performed in 17 (25.0%) of cases. Most patients received combined aspirin and thienopyridin treatment for 6 or 12 months after the procedure. Technical success was obtained in 62 (91.2%) treated lesions and in-hospital major adverse cardiac events occurred in 4.5%. At follow up, mean (SD) reference diameter was 4.20 (0.53) mm, minimum lumen diameter 2.94 (1.50) mm, and late loss 0.86 (1.25) mm. The overall major adverse cardiac events rate was 26.7%.

CONCLUSION

VBT of SVG is feasible and safe. At follow up the reintervention rate and cardiac morbidity and mortality seem to be favourable, considering that interventions in SVG usually are associated with the highest risks.

Time course of stent endothelialization after intravascular radiation therapy in rabbit iliac arteries

BACKGROUND

Late total occlusion after vascular brachytherapy (VBT) continues to be a serious complication. Delayed reendothelialization was suggested as a pivotal cause, but the time course for complete healing is unknown.

METHODS AND RESULTS

Seventy-two rabbit iliac arteries underwent stent implantation and were treated with gamma-radiation using 192Ir. The prescribed doses were 0 Gy (controls, n=24 arteries), 15 Gy (n=24), or 30 Gy (n=24) at 2 mm. Animals were killed at 1 month (n=24), 3 months (n=24), or 6 months (n=24) and were analyzed for histomorphometry or scanning electron microscopy. Intimal area was reduced after VBT at 3 months with 15 and 30 Gy (0.66+/-0.07 and 0.66+/-0.04 mm2, respectively) compared with controls (1.01+/-0.11 mm2, P<0.05) and at 6 months with 30 Gy (0.75+/-0.09 versus 1.28+/-0.26 mm2 in controls, P<0.01). Intimal area was similar at 6 months between 15 Gy and controls. At 1 month, 92+/-4% of the control stented segment was covered with endothelial cells, whereas only 37+/-4% and 37+/-8% was covered in the 15- and 30-Gy arteries, respectively. Similarly, at 3 and 6 months, there was a difference in the extent of reendothelialized areas (at 3 months, 95+/-2%, 32+/-12%, and 29+/-13%; and at 6 months, 98+/-2%, 40+/-8%, and 35+/-12% in control, 15-Gy, and 30-Gy arteries, respectively). Excess platelets and leukocytes were seen in irradiated arteries without complete coverage of endothelium.

CONCLUSIONS

Reendothelialization after VBT is not completed at 6 months after VBT. Special care with prolonged antiplatelet therapy should be considered beyond that time point.

A morphological–mechanical explanation of edge restenosis in lesions treated with vascular brachytherapy

PURPOSE

Edge restenosis in stenotic lesions treated by implantation of a conventional stent followed (or preceded) by a catheter-based brachytherapy is often attributed to "geographic miss" (GM). We propose a complementary (or, possibly, alternative) explanation based on the concept that a clear postprocedural mismatch between the in-stent lumen and the normal (undilated) lumens of the proximal and/or distal vessel segments results in an excessive, damageable increase of axial wall stress in these segments.

METHODS

The possible poststenting situations at both margins of a stent are examined, and based on the presence or absence of an increase in axial wall stress, predictions are made about the lesion evolution. The concept is then also examined in the light of published observations.

RESULTS

None of the analyzed observations appeared to be incompatible with the proposed morphological-mechanical explanation.

CONCLUSION

From a mechanical point of view, optimal matching of the proximal and distal stent diameters to the corresponding normal diameters of the adjacent arterial segment is likely to reduce the rate of edge restenosis.

Beta emitter systems and results from clinical trials

Vascular brachytherapy has been established as the standard of care for the treatment of in-stent restenosis (ISR). Both beta and gamma emitters are currently in use for the prevention of ISR recurrence. The use of beta sources for vascular application is attractive from both the radiation exposure and safety points of view, and a wide variety of beta sources are available for this application. This review is intended to summarize the clinical trials utilizing beta emitter systems for the treatment of ISR and de novo lesions and their subsequent results.

Dosimetry for an Sr90/Y90 source train used for intravascular radiation of a hemodialysis graft

OBJECTIVE

Vascular access for hemodialysis is often achieved with an arterial-venous graft (AVG). Brachytherapy is being explored for prevention of stenosis within these grafts. The objective was to develop treatment planning (TP) capability for dialysis implants.

MATERIALS AND METHODS

Fluoroscopic images are used to identify position of sources and irradiated vessel. An Sr(90)/Y(90) beta source, jacketed in a CO(2)-filled balloon, is used to irradiate the AVG. A single-seed Sr(90) dose kernel was generated using Monte Carlo. The single-seed dose kernel was employed to calculate the dose surrounding the implant accounting for the path length of the beta particles through the gas-filled balloon.

RESULTS

Dose distributions are displayed superimposed on the fluoroscopic image of the AVG. Dose-area histograms were also generated.

CONCLUSION

TP for dialysis implants can be performed using radiographic localization of the graft. The TP tools could be used to correlate clinical outcome with dose delivery.

Debulking does not benefit patients undergoing intracoronary beta-radiation therapy for in-stent restenosis: insights from the START trial

Intracoronary brachytherapy has become the current treatment of choice for patients with in-stent restenosis (ISR). The aim of the present study was to determine whether plaque extraction using debulking techniques prior to brachytherapy would improve the outcomes of patients with ISR. Patients enrolled into the START (n = 476) and START-40 (n = 205) trials were divided into four subgroups according to their treatment assignments: debulking-radiation, debulking-placebo, balloon angioplasty (BA) radiation, and BA placebo. Patients were further divided according to their ISR lesion length: all lesions, > 15 mm, and > 19 mm. Restenosis rates were higher in placebo, nonradiated lesions undergoing debulking (52.7%) vs. BA alone (38.5%; P = 0.04). Postprocedural minimal lumen diameter (MLD) was similar among the subgroups. Outcomes were similar between debulking and BA within each therapeutic arm. MLD after debulking radiation was greater in patients with ISR > 15 mm (post-MLD was 1.9 vs. 1.7 mm; P = 0.06) but not in the placebo. Debulking radiation patients had greater MLD at follow-up, but restenosis (23.5% after debulking vs. 32.7% BA alone) and late loss (0.3 mm in both subgroups) were not statistically different. There was a trend toward higher mortality among debulked patients (3.7%) compared to BA alone (0.8%). In patients with ISR > 19 mm, four patients died following debulking radiation as compared to no death after BA (P = 0.05). Our results do not support the strategy of plaque extraction prior to intracoronary beta-radiation for ISR.

Intracoronary beta-brachytherapy in chronic total occlusions: a subgroup analysis from the RENO registry

Conventional interventional therapy has been less rewarding in chronic total occlusion (CTO). Brachytherapy by its antiproliferative and positive remodeling effect may be more efficacious. Forty-six centers registered 1,098 consecutive patients undergoing brachytherapy with the BetaCath system. Of these, 78 patients had 82 lesions (CTO) at presentation-the study population. With 67% in-stent CTO, 8% graft CTO, 4% recurrent CTO, long lesions (27.6 +/- 20.9 mm), and 31% diabetes, the cohort had high risk for recurrence. The in-hospital event rate was 1.3%. Six-month follow-up revealed 1.3% death, 5.1% myocardial infarction, 21.8% target vessel revascularization, 77.8% improved angina, 34.5% binary restenosis, 12.7% reocclusion, and 10.3% late thrombosis. The results were comparable to all other patients in the registry, although late thrombosis rate was higher in the CTO group (10.3% vs. 5.0%; P = 0.047). In the in-stent CTO subgroup (n = 52; 66.7%), there was no in-hospital event, no follow-up death or myocardial infarction, restenosis in 35.1%, and reocclusion in 10.8% of patients. In comparison, death or myocardial infarction was significantly higher in de novo CTO subgroup (P = 0.005). Compared to all other in-stent restenosis patients in the registry, the patients with in-stent CTO had similar clinical and angiographic event rate. Thus, beta-brachytherapy was safe, feasible, and effective in this broad population of high-risk patients with CTO presenting in day-to-day practice. It was particularly effective in in-stent CTO, where conventional interventional strategies are disappointing.