Endoluminal beta-radiation therapy for the prevention of coronary restenosis after balloon angioplasty. The Dose-Finding Study Group

Optimizing dosimetry with high-dose intracoronary gamma radiation (21 Gy) for patients with diffuse in-stent restenosis

BACKGROUND

The efficacy of intracoronary gamma radiation (IRT-gamma) in reducing recurrent in-stent restenosis (ISR) is well established using doses of 14-18 Gy. We sought to examine whether an escalation in dose to 21 Gy is safe and confers additional benefit in reducing repeat revascularization and major adverse cardiac events (MACE) in patients with diffuse ISR.

METHODS

Forty-seven patients with diffuse ISR (lesion length 20-80 mm) in native coronary arteries (n=25) and saphenous vein grafts (n=22) underwent percutaneous transluminal coronary angioplasty and/or additional stents followed by IRT-gamma using the Checkmate system (Cordis) with a dose of 21 Gy. All patients were discharged with clopidogrel for 12 months and aspirin indefinitely. Six-month angiographic and 12-month clinical outcomes of these patients were compared to 120 patients treated with 18 Gy using the same system.

RESULTS

At baseline, patients in the 21-Gy group had more multivessel, vein graft disease and history of prior myocardial infarctions and coronary artery bypass grafts (P<.001). The use of debulking devices and stents was less in this group (P<.001). Procedural and in-hospital complications were similar. Follow-up at 6 months revealed nonsignificant but lower late loss (in-stent, 0.33+/-0.7 mm; in-lesion, 0.41+/-0.6 mm) in the 21-Gy group compared to the 18-Gy group; follow-up at 12 months revealed a trend toward less overall myocardial infarction, although repeat revascularization and MACE rates were similar.

CONCLUSIONS

IRT-gamma therapy for diffuse ISR lesions with a 21-Gy dose is clinically safe and feasible with marked reduction in late loss but does not confer additional benefit with regard to repeat revascularization and MACE when compared to a dose of 18 Gy.

External Beam Radiation to Prevent Restenosis After Superficial Femoral Artery Balloon Angioplasty

Background— Femoropopliteal percutaneous transluminal angioplasty (PTA) remains limited by restenosis. Although vascular brachytherapy may be effective in reducing restenosis, external beam radiation would be more practical to administer after PTA.

Methods and Results— After femoropopliteal PTA without stent placement, 99 patients were randomly assigned to 0 Gy (placebo; n=24), 7 Gy (n=24), 10.5 Gy (n=26), or 14 Gy (n=25) of external beam radiation of the PTA site (with a 3-cm margin at both extremities) in 1 session 24 hours after PTA. The primary end point was minimum lumen diameter on quantitative angiography 1 year after PTA. One year after PTA, the mean minimum lumen diameter was 1.92, 1.64, 1.92, and 2.91 mm, respectively, for the 0-, 7-, 10.5-, and 14-Gy groups ( P =0.0072 for 0 versus 14 Gy). Mean luminal loss was 1.14, 1.27, 1.08, and 0.14 mm, respectively, for the 4 groups ( P =0.0072 for 0 versus 14 Gy). Restenosis >50% was present in 50%, 65%, 48%, and 25% of patients, respectively, for the 0-, 7-, 10.5-, and 14-Gy groups ( P =0.072). At 18 months, repeated revascularizations were required in 25% of patients in the 0-Gy group versus 12% of patients in the 14-Gy group ( P =0.24).

Conclusions— A single session of external beam radiation of 14 Gy of the femoropopliteal angioplasty site significantly reduces restenosis at 1 year.

Effects of probucol versus aspirin and versus brachytherapy on restenosis after femoropopliteal angioplasty: the PAB randomized multicenter trial

PURPOSE

To evaluate the effect of probucol and/or of endovascular brachytherapy (EVBT) on restenosis after percutaneous transluminal angioplasty (PTA) of femoropopliteal arteries.

METHODS

A total of 335 patients (206 men; mean age 72+/-9 years) with intermittent claudication were randomized according to a 2x2 factorial design to 1 of the 4 groups: probucol, placebo, EVBT, and EVBT+probucol. Probucol (1 g/d) or placebo were given in double-blinded fashion 1 month before and for 6 months after PTA. Gamma irradiation (192Iridium, 14 Gy, 5-mm reference depth) was randomly applied in an unblinded manner from a noncentered endoluminal catheter. All patients received aspirin (100 mg/d). Primary endpoint was restenosis (>50% diameter reduction) detected by duplex ultrasound 6 months after PTA. Secondary endpoints included clinical and hemodynamic assessment.

RESULTS

Restenosis in patients undergoing EVBT was 17% (23/133) versus 35% (50/142) in patients without EVBT (p<0.001); in patients treated with probucol versus placebo, the rates were 23% (31/135) and 30% (43/140, p<0.001). Three quarters (77%, 102/133) of patients were free of claudication after EVBT therapy versus 61% (87/142) without EVBT (p<0.05). Need for target vessel revascularization was 6% (8/133) with EVBT versus 14% (20/142) without EVBT (p<0.01). Late thrombotic occlusions occurred in 4% (6/133), exclusively in patients treated with EVBT after stent implantation.

CONCLUSIONS

Endovascular brachytherapy significantly reduces restenosis, improves symptoms, and reduces reinterventions after PTA of femoropopliteal arteries. Probucol reduces restenosis but has no additive effect when combined with brachytherapy.

Quantification of dose perturbation by plaque in vascular brachytherapy

BACKGROUND

Dose prescription and reporting in vascular brachytherapy (VBT) is based on the assumption that the vessel wall is water equivalent, which does not consider a possible dose perturbation by plaque. As the extent of this perturbation is unknown, we aimed to quantify dose attenuation by atherosclerotic plaque for beta- and gamma-radiation.

MATERIAL AND METHODS

The dose delivered from Strontium-90/Yttrium-90 ((90)Sr/Y) and Iridium-192 ((192)Ir) sources with and without human peripheral arteries ((90)Sr/Y: n = 38, (192)Ir: n = 7) surrounding the respective delivery catheter was determined with radiochromic films. Plaque and vessel wall thickness were measured using light microscopy. From the ratio-attenuated doseunattenuated dose (dose perturbation factor: DPF) we determined averaged attenuation coefficients for atherosclerotic plaque (micro(P)) and the residual part of the vessel wall (micro(W)) by regression analysis based on the function DPF = exp(-micro(P) * plaque thickness -micro(W) * residual wall thickness).

RESULTS

Attenuation in case of (192)Ir was less than the measurement uncertainties. For beta-radiation correlation was found by discrimination between calcified and noncalcified plaque. Classifying noncalcified plaque as normal arterial tissue, the regression coefficient was r = 0.845 at micro(P)= 0.5356 mm(-1) and micro(W) = 0.0663 mm(-1).

CONCLUSIONS

Vascular brachytherapy with beta radiation in calcified arteries results in significant dose attenuation within the vessel wall, which can be calculated on knowing the vascular morphometry. Thus, plaque thickness should be taken into account in treatment planning and retrospective analyses.

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.

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

BACKGROUND

This study evaluated vascular brachytherapy (VBT) as a potent antiproliferative treatment to prevent in-stent restenosis (ISR) after coronary angioplasty of de novo lesions in patients carrying the D allele of the I/D polymorphism of the ACE gene and high ACE plasma levels (>34 U/l).

METHODS AND MATERIALS

A prospective randomized trial was designed to detect a 30% improvement in the minimal lumen diameter (MLD) of the stenotic artery, as measured by quantitative coronary analysis (QCA), 6 months following VBT at the time of stented angioplasty. All patients were carriers of the D allele of the ACE gene, with plasma ACE levels >34 U/l.

RESULTS

Thirty-one patients (33 stenoses) were allocated to stent implantation (control group) and 30 patients (31 stenoses) to VBT and stented angioplasty. After angioplasty, in-stent MLD was similar in the two groups. At 6 months in the control group, in-stent MLD had decreased to 1.74+/-0.8 versus 2.25+/-1.05 mm in the VBT group (P=.04). The mean in-stent diameter was 2.3+/-0.8 mm in the control group versus 2.9+/-1.05 mm after VBT (P=.02), and the restenosis rate was 37.5% versus 17.9%, respectively (P=.08). At 6 months, a higher need for target vessel revascularization (TVR) was observed in the control group: 35.5% versus 13.3% (P=.04).

CONCLUSIONS

This randomized study confirms that patients with high plasma ACE concentrations are exposed to an increased risk for ISR after coronary stenting. The preventive use of VBT in these patients reduced neointimal formation by 65% such that the MLD at follow-up was increased by 29% compared with the control group.

Angiographic and three-dimensional intravascular ultrasound analysis of combined intracoronary beta radiation and self-expanding stent implantation in human coronary arteries

This study tested the combination of vascular brachytherapy (VBT) and self-expanding Wallstent implantation in coronary lesions of patients at high risk for restenosis as assessed angiographically by quantitative coronary analysis and by 3-dimensional intravascular ultrasound analysis. Twenty-nine "de novo" lesions were managed with a self-expanding stent alone (n = 19) or with a self-expanding stent after beta-VBT (n = 10) in 27 patients who had been identified by high levels of plasma angiotensin-converting enzyme as being prone to myointimal growth after stent implantation. At 6 months, the increase in stent strut diameter was similar in the 2 groups by quantitative coronary analysis and 3-dimensional intravascular ultrasound (Delta mean stent strut diameter -0.33 +/- 0.3 vs -0.40 +/- 0.3 mm, p = 0.5; Delta stent area -11.8 +/- 6.1 vs -12.0 +/- 6.1 mm(2), p = 0.9; Delta stent volume -96.9 +/- 112 vs -83.5 +/- 73 mm(3), p = 0.7; for groups treated with VBT and self-expanding stents and only self-expanding stents, respectively). In-stent neointimal proliferation was decreased in the group treated with VBT and self-expanding stents (minimal luminal diameter 2.5 +/- 0.8 vs 1.88 +/- 0.8 mm, p = 0.04) by quantitative coronary analysis (minimal luminal area 6.7 +/- 2.5 vs 4.1 +/- 1.9 mm(2), p = 0.01), by intravascular ultrasound, and proliferation volume (84.6 +/- 66.4 vs 159.2 +/- 103.5 mm(3), p = 0.05) by 3-dimensional intravascular ultrasound. Positive vessel and luminal remodelings were observed in 50% of the group treated with VBT and self-expanding stents and in 11% of the group treated only with self-expanding stents (p = 0.02). The combined use of VBT and self-expanding stents is a novel approach that enlarges vascular lumen by preventing vessel constriction and neointimal proliferation. The feasibility and good results of this experimental approach suggest that the simultaneous use of these 2 technologies may be an interesting alternative for difficult vascular districts with high restenosis rates, such as peripheral circulation in the lower limbs.

External heating of stents by radio waves: pilot studies in rabbit aorta

PURPOSE

This experiment was designed to assess the feasibility of radio frequency energy delivered by a prototype radio frequency generator inductive heating device (REVAX) positioned external to the body, for transient heating of stents after arterial implant.

METHODS AND MATERIALS

Twenty-one New Zealand White rabbits underwent stenting of their infrarenal aorta. Nine rabbits were stented and immediately placed in the REVAX for external stent heating with internal temperature probes in place. Twelve rabbits were stented and 3 days later either heated or placed in the generator as a sham for 20 min. The animals were terminated 28 days later.

RESULTS

The REVAX was able to heat the aortic stents in a controlled fashion; in Phase II experiments, the stent temperature was raised to 42 degrees C for 20 min. In Phase I mild necrosis was noted at the stent struts. In Phase II, necrosis and mineralization of the media was seen at the stent struts, and evidence of neointimal suppression was observed.

CONCLUSION

This study demonstrated that external heating of stents in a blood vessel in a live animal via radio frequency energy is feasible. Further studies will be needed to assess whether any specific heating regimen might inhibit fibrocellular neointimal hyperplasia.

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.

Basic treatment planning parameters for a 90Sr / 90Y source train used in endovascular brachytherapy

Working groups of the AAPM, DGMP, and ESTRO have published recommendations for endovascular brachytherapy, introducing concepts of relevant parameters for dose specification and treatment planning. However, the procedures for this treatment remain often mainly based on trial protocols and manufacturer instructions. Treatment planning requires the essential knowledge of the radial and longitudinal dose distribution, as well as information about geometrical uncertainties. The present study includes a whole data set for daily clinical practice using a commercially available device for endovascular brachytherapy (Novoste Betacath). The dose distribution around the 90Sr seed train was calculated with Monte-Carlo algorithms and verified by film dosimetry. The radial dose profile was determined starting from the surface of the delivery catheter Calculated dose profiles were in good agreement to measured values. The geometrical uncertainties were estimated with a retrospective analysis of 51 patient treatments. This shows the importance of using a safety margin of at least 10 mm between Intervention Length and Reference Isodose Length. Based on the longitudinal dose profile and the necessary safety margins, the maximum treatable intervention length is 25 mm and 45 mm for a 40 mm and 60 mm source train, respectively.

Relation of clinical success in coronary brachytherapy to dose

Intravascular brachytherapy is the primary treatment for coronary in-stent restenosis. Variations in dose in the treated artery may represent a potential cause of treatment failure. We compared dose distributions in patients who had developed recurrent restenosis (treatment failure) with those in patients who remained event free at 9 months (treatment success). We followed 140 patients who were receiving brachytherapy for in-stent restenosis with 4 radiation delivery devices to identify treatment failures and successes. Through a nested case-control construct, treatment failures (n = 14) were compared 1:2 with treatment successes (n = 28) matched by radiation delivery system and in-stent restenosis lesion pattern. The dose absorbed by 90% of the artery encompassed by the external elastic membrane (D(90)EEM) was calculated by applying intravascular ultrasound at 2-mm intervals along the treated lesion. Dose calculations were performed using dose kernel integration techniques generated from Monte Carlo simulations. The mean minimum D(90)EEM in treatment failures was 7.46 +/- 1.98 Gy, and that in treatment successes was 8.87 +/- 1.13 Gy (p = 0.007). Using a minimum dose threshold of 8.4 Gy, a minimum D(90)EEM <or=8.4 Gy occurred in 13 patients (93%) whose treatment failed but only in 9 patients (32%) whose treatment was a success (p <or=0.001). No confounding variables were found to be statistically significant between treatment failures and successes. In conclusion, current brachytherapy dose prescriptions allow for inter- and intralesion variations in dose. Arteries that receive <or=8.4 Gy at any point along the external elastic membrane are more likely to result in treatment failures. Dosimetry guided by intravascular ultrasound may be critical to ensure adequate dose delivery and outcomes.

Patient doses in gamma-intracoronary radiotherapy: the Radiation Burden Assessment Study

PURPOSE

To determine accurately the radiation burden of both patients and staff from intracoronary radiotherapy (IRT) with (192)Ir and to investigate the importance of IRT in the patient dose compared with interventional X-rays.

METHODS AND MATERIALS

The Radiation Burden Assessment Study (RABAS) population consisted of 9 patients undergoing gamma-IRT after percutaneous transluminal coronary angioplasty and 14 patients undergoing percutaneous transluminal coronary angioplasty only as the control group. For each patient, the dose to the organs and tissues from the internal and external exposure was determined in detail by Monte Carlo N-particle simulations. Patient skin dose measurements with thermoluminescence dosimeters served as verification. Staff dosimetry was performed with electronic dosimeters, thermoluminescence dosimeters, and double film badge dosimetry.

RESULTS

With respect to the patient dose from IRT, the critical organs are the thymus (58 mGy), lungs (31 mGy), and esophagus (27 mGy). The mean effective dose from IRT was 8 mSv. The effective dose values from interventional X-rays showed a broad range (2-28 mSv), with mean values of 8 mSv for the IRT patients and 13 mSv for the control group. The mean dose received by the radiotherapist from IRT was 4 microSv/treatment. The doses to the other staff members were completely negligible.

CONCLUSION

Our results have shown that the patient and personnel doses in gamma-IRT remain at an acceptable level. The patient dose from IRT was within the variations in dose from the accompanying interventional X-rays.

Local drug delivery in restenosis injury: thermoresponsive co-polymers as potential drug delivery systems

The success of percutaneous transluminal coronary angioplasty in treatment of acute coronary syndromes has been compromised by the incidence of restenosis. The physical insult of balloon insertion can damage or remove the endothelial monolayer, thereby generating a prothrombotic surface. The resulting inappropriate response to injury can also lead to penetration of inflammatory cells, conversion of the underlying media to a synthetic phenotype, deposition of extracellular matrix, constrictive remodeling, and neointimal hyperplasia. While stent implantation at the time of balloon insertion has offset some of these events, inflammatory responses to the implanted biomaterial (stent) and intimal hyperplasia are still prominent features of the procedure, leading in 20-30% of cases to in-stent restenosis within a year. Systemic delivery of drugs designed to offset in-stent restenosis injury has been largely unsuccessful, which has led to the development of strategies for coating stents with drugs for local delivery. Drug-eluting stents constitute an innovative means of further reducing the incidence of restenosis injury and clinical trials have shown encouraging results. This review focuses on properties of a class of environment-sensitive hydrogels, the N-isopropylacrylamide-based thermoresponsive co-polymers, on their potential roles as stent coatings, on their demonstrated ability to incorporate and release drugs that modify vascular endothelial and smooth muscle cell functions, and on issues that still await clarification, prior to their adoption in a clinical setting.

A novel method of brachytherapy using local delivery of 99mTc-HMPAO for coronary stent restenosis

BACKGROUND

Restenosis after percutaneous coronary intervention (PCI) is a matter that still remains to be resolved. Herein, the inhibitory effect of locally delivered 99mTc-HMPAO (hexamethyl propylene amine oxime) on neointimal hyperplasia after coronary stenting was examined in a pocine model, and its safety and efficacy observed in patients with coronary stent restenosis.

METHODS

After a stent overdilation injury, local radioisotope delivery using 99mTc-HMPAO was applied to one coronary artery (Group I) and control therapy to another (Group II) in each of 10 pigs. Follow-up coronary angiogram (CAG) and histopathologic assessment were performed 4 weeks after stenting. Eleven patients (10 males and one female, 62.4 +/- 5.7 years of age) underwent local administration of 30 mCi/ 2 mL 99mTc-HMPAO shortly after PCI, via a Dispatch Catheter, followed by a whole body scan to evaluate the distribution of the 99mTc-HMPAO, as well as a thallium-201 (TI-201) myocardial scan to evaluate myocardial perfusion. The major adverse cardiac events (MACE) were assessed during a one-year clinical follow-up.

RESULTS

On histopathological analysis, the neointimal areas were 1.2 +/- 0.6 and 2.7 +/- 0.4 mm2 (p=0.002), and the histopathological areas of stenosis were 27.16.3 and 53.4 +/- 5.2% in Groups I and II (p=0.001), respectively. In the clinical study, there was no in-hospital MACE. On a quantitative coronary angiographic analysis, the minimal luminal diameter was increased from 0.4 +/- 0.3 to 2.9 +/- 0.2 mm, and diameter stenosis decreased from 84.2 +/- 9.5 to 16.3 +/- 11.0% following PCI. Follow-up CAG was performed in 9 cases (81.8%) and restenosis occurred in 2 (22.2%). On a follow-up CAG, the minimal luminal diameter, diameter stenosis rate, lumen loss and loss index were 2.0 +/- 0.8 mm, 27.7 +/- 2.9%, 0.7 +/- 0.7 mm and 0.2 +/- 0.3, respectively. During the one-year clinical follow-up there were no cases of death or acute MI, but two cases of target vessel revascularization (18.2%).

CONCLUSION

Local delivery of 99mTc-HMPAO, a novel radiotherapy, can be used safely and effectively for coronary stent restenosis.

Prevention of restenosis after coronary angioplasty

PURPOSE OF REVIEW

Despite numerous advances in coronary interventional techniques, the frequent occurrence of restenosis continues to plague interventional cardiology. With the widespread use of drug-eluting stents, there is a need to reexamine critically the roles of the various interventional techniques currently available.

RECENT FINDINGS

Drug-eluting stents have dramatically reduced the rates of restenosis and target vessel revascularization in a wide spectrum of patients with varying lesion morphologies. However, when restenosis does occur, it still tends to be dependent on the same factors that predict restenosis with bare metal stenting. The routine use of drug-eluting stents entails high initial costs to the health care system. Debulking as a means to improve outcomes after angioplasty has not lived up to expectations. Gene therapy is rapidly evolving into a viable means to reduce neointimal proliferation after angioplasty.

SUMMARY

Careful patient selection and attention to the procedure of stent deployment optimize the results of angioplasty with drug-eluting stents. Because of cost considerations, drug-eluting stents should be used in patients who are expected to have the greatest absolute benefit. In this context, when judiciously used, conventional balloon angioplasty and bare metal stenting still have a definite role in the management of patients with obstructive coronary artery disease.

Effects of Percutaneous Transluminal Angioplasty and Endovascular Brachytherapy on Vascular Remodeling of Human Femoropopliteal Artery by Noninvasive Magnetic Resonance Imaging

Background— Percutaneous transluminal angioplasty (PTA) of severely stenotic peripheral vascular lesions is hampered by a higher restenosis rate. The effects of PTA on vascular wall as well as the effects of the antirestenotic properties of endovascular brachytherapy (EVBT) remain unclear. MRI allows in vivo noninvasive assessment of the vascular effects of such treatment strategies. We sought to elucidate the vascular effect of PTA and PTA+EVBT by serial MRI.

Methods and Results— Twenty symptomatic patients with severe stenosis of the femoropopliteal artery were randomly assigned to PTA (n=10) or PTA+EVBT (n=10; 14 Gy by γ-irradiation source) and imaged by high-resolution MRI before and 24 hours and 3 months after intervention. An independent observer blinded to the procedure analyzed the MRI data. At 24 hours, cross-sectional MRI revealed that lumen area (86% and 67%) and total vessel area (47% and 34%) increased similarly in the PTA and PTA+EVBT groups, respectively. All patients showed severe splitting of the atherosclerotic plaque, resulting in an irregularly shaped lumen. At 3 months, MRI revealed a significant difference in lumen area change between the PTA and PTA+EVBT groups (40% and 106%, respectively; P =0.026) and in the total vessel area (14% and 39%, respectively; P =0.018). At 3 months, plaque disruption was still present in 50% of the patients treated with PTA+EVBT.

Conclusions— After PTA, there is deep disruption of the atherosclerotic plaques and an extensive remodeling process of the arterial wall. Luminal loss after PTA is partially due to inward vessel remodeling. Brachytherapy prevents inward remodeling and induces an increase in lumen area but partially prevents healing of disrupted vessel surface.

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.

Clinical quality assurance for endovascular brachytherapy devices

BACKGROUND AND PURPOSE

Endovascular brachytherapy is still an important therapy modality with a high number of treated patients per year. Quality assurance of devices used has been addressed already in several publications (AAPM, DGMP, ESTRO, NCS). However, there are no clear recommendations given on test procedures and related equipment. Our experience with four different devices containing beta- ((32)P, (90)Sr/Y) and gamma-sources ((192)Ir), which were used in clinical routine during the last 3 years is described.

PATIENTS AND METHODS

The incoming check includes leakage radiation, missing catheter interlock, positioning test, timer check, interrupt button check, power-off test and verification of the manual retraction facility. Dose profiles are measured using GafChromic film. Source strength verification is performed using well type chambers or air-kerma measurements. In addition, the proposed reference absorbed dose rate at 2 mm distance from the source centre is measured with a dedicated film dosimetry technique where two additional films are exposed to two known doses in a (60)Co field for calibration.

RESULTS

Dosimetrical parameters (dose profiles, source strength) are found to be within +/-10% of the manufacturers specifications. The reference dose rate measured with film is on average +3.1% for 13 (90)Sr seed trains, +8.1% for three (32)P wire sources and -3.7% for one (192)Ir seed ribbon compared to the source certificate. The activity of 30 individual (32)P wire sources measured by using a calibrated well type chamber showed a deviation of mean -0.3%, the activity of 16 (192)Ir seed ribbons determined with air kerma measurements a deviation of mean 2.8%.

CONCLUSIONS

The QA programme introduced in our department provides methods to verify all relevant parameters proposed by international recommendations. Film dosimetry can be used as independent verification of the reference dose rate within a 10% limit.

Intracoronary Brachytherapy After Stenting De Novo Lesions in Diabetic Patients

OBJECTIVES

We studied the efficacy of intracoronary brachytherapy (ICB) after successful coronary stenting in diabetic patients with de novo lesions.

BACKGROUND

Intracoronary brachytherapy has proven effective in preventing recurrences in patients with in-stent restenosis. However, the role of ICB for the treatment of de novo coronary stenoses remains controversial.

METHODS

Ninety-two patients were randomized to either ICB or no radiation after stenting. Primary end points were in-stent mean neointimal area (primary end point of efficacy) and minimal luminal area of the entire vessel segment (primary end point of effectiveness), as assessed by intravascular ultrasound at six-month follow-up. Quantitative coronary angiography analysis was performed at the target, injured, irradiated, and entire vessel segments.

RESULTS

At follow-up, the in-stent mean neointimal area was 52% smaller in the ICB group (p < 0.0001). However, there was no difference in the minimal luminal area of the vessel segment (4.5 +/- 2.4 mm2 vs. 4.4 +/- 2.1 mm2). Restenosis rates increased progressively by the analyzed segment in the ICB group: target (7.1% vs. 20.9%, p = 0.07), injured (9.5% vs. 20.9%, p = NS), irradiated (14.3% vs. 20.9%, p = NS), and vessel segment (23.8% vs. 25.6%, p = NS). At one year, 1 cardiac death, 6 myocardial infarctions (MIs) (3 due to late stent thrombosis), and 10 target vessel revascularizations (TVRs) (6 due to the edge effect) occurred in the ICB group, whereas in the nonradiation group, there were 11 TVRs and no deaths or MIs.

CONCLUSIONS

Intracoronary brachytherapy significantly inhibited in-stent neointimal hyperplasia after stenting in diabetic patients. However, clinically this was counteracted by the occurrence of the edge effect and late stent thrombosis.

Direct Stenting Versus Direct Stenting Followed by Centered Beta-Radiation With Intravascular Ultrasound-Guided Dosimetry and Long-Term Anti-Platelet Treatment

OBJECTIVES

We sought to assess the efficacy of vascular brachytherapy (VBT) combined with stenting for the primary prevention of restenosis.

BACKGROUND

Intravascular brachytherapy after stent implantation for de novo lesions has been abandoned for the present. We revisited this procedure by optimizing all procedural steps-the use of glycoprotein IIb/IIa blockers, direct stenting, adequate radiation coverage, avoidance of edge damage, source centering, intravascular ultrasound-guided dosimetry, and continuation of a dual anti-platelet regimen for one year.

METHODS

The Beta-Radiation Investigation with Direct stenting and Galileo in Europe (BRIDGE) study is a multicenter, randomized controlled trial evaluating the long-term efficacy of VBT with P-32 (20 Gy at 1 mm in the coronary wall) after direct stenting. The primary end point was angiographic intra-stent late loss; secondary end points were six months binary restenosis and neo-intimal hyperplasia. Patients (n = 112) with de novo lesions (2.5 to 4.0 mm in diameter up to 15 mm long) were randomized to either VBT or no-VBT.

RESULTS

At six months, intra-stent loss was 0.43 and 0.84 mm (p < 0.001) in the irradiated and control groups, respectively. Intra-stent neo-intimal volume was reduced from 36 mm3 to 10 mm3. However, in the irradiated group there were six late occlusions as well as eight restenoses outside the stented and peri-stented area at the fall-off dose edges of the irradiated area. Accordingly, the target vessel revascularization and major adverse cardiac and cerebrovascular events rates at one year in the VBT group (20.4% and 25.9%, respectively) were higher than in the control group (12.1% and 17.2%, respectively).

CONCLUSIONS

Despite the optimization of pre-, peri-, and post-procedural factors and despite the relative efficacy of the brachytherapy for the prevention of the intra-stent neo-intimal hyperplasia, the clinical outcome of the irradiated group was less favorable than that of the control group.

External beam radiotherapy fails to prevent restenosis after iliac or femoropopliteal percutaneous transluminal angioplasty: results of a prospective randomized double-blind study

PURPOSE

Early restenosis is one of the major complications after successful percutaneous transluminal angioplasty (PTA), in main, as well as peripheral, arteries. The effectiveness of hypofractionated external beam radiotherapy (EBRT) as a prophylaxis for restenosis was examined in a prospective, randomized, double-blind, clinical trial.

METHODS AND MATERIALS

Forty-eight patients underwent sham RT and 47 were treated with daily RT in 3-Gy fractions, to a total dose of 21 Gy. The follow-up lasted for 12 months, and the examinations included pressure measurements and calculations of the ankle-brachial index or duplex sonography ("peak velocity ratio"). If restenosis was suspected, additional angiography was performed.

RESULTS

No statistically significant difference was found between the treatment groups: sham RT 16 failures (33.3%) and EBRT group 21 failures (45.7%; p = 0.292). EBRT also showed no substantial effects on subgroups classified by the specific length of the lesion or in diabetic patients.

CONCLUSION

External beam radiotherapy does not prevent restenosis. A reduction in the failure rate >8% using fractionated EBRT with doses aimed at keloid prevention can be ruled out with a probability of 97.5%. Endovascular brachytherapy remains the preferred therapeutic method for achieving restenosis prophylaxis through RT.

"Candy wrapper" effect after drug-eluting stent implantation: déjà vu or stumbling over the same stone again?

Encouraging results have been obtained with drug-eluting stents (DESs) to prevent restenosis following PCI. However, DESs are not immune from restenosis and we describe a case of "candy wrapper" effect, commonly observed with intracoronary brachytherapy (IBT). In this article, we review the common drawbacks of DES and IBT and their prevention.

Quality assurance in intracoronary brachytherapy. Recommendations for determining the planning target length to avoid geographic miss

BACKGROUND AND PURPOSE

A new method of assessing geographic miss (GM) in endovascular brachytherapy (EVBT) is applied to evaluate the quality of intracoronary brachytherapy treatments, retrospectively. Based on the Vienna experience, recommendations for adequate safety margins are derived to avoid GM.

PATIENTS AND METHODS

Evaluation is done on 136 vessels of 128 consecutive patients treated between October 1999 and July 2001. The quality of EVBT is assessed using the concept and terminology of the EVA GEC ESTRO task group. Evaluation of GM and/or safety margin is performed by comparing the outermost interventions with the reference isodose length (RIL) of the applied delivering devices on recorded compact disk (CD) angiograms. The RIL is defined as the length of the vessel segment, which receives at least 90% of the reference dose at the reference depth (=1 mm within the vessel). GM is defined as injured vessel segments, which receive a dose lower than 90% of reference dose. Measurements of intervention length (IL) and active source length (ASL) are performed with respect to anatomical landmarks within the vessel in the region of interest (e.g. stent edges), and by using the nominal length of the devices (balloons, sources) as a reference scale. The edges of RIL are determined by subtracting the length of the dose-fall-off zone (specific to the applied delivery devices: (192)Ir 4.5 mm, (90)Sr 2.5 mm, (32)P 2.0 mm) from the edges of ASL.

RESULTS

The described method to assess GM is applicable to 128 vessels (94%). GM is found in 23% of proximal edges and 20% of distal edges. 95% of all GM are observed if the total margin (proximal+distal margin) between RIL and IL is shorter than 10.5 mm.

CONCLUSIONS

GM in intracoronary brachytherapy can be widely avoided by adding an appropriate safety margin to the IL (5-6 mm each edge in this study) in order to determine the necessary RIL for a treatment.

[In 2003, what are the indications of brachytherapy in coronary arteries?]

Significant results obtained with coated stents in "de novo" coronary lesion treatment, particularly in complex lesions, have substituted brachytherapy indications. However, curitherapy results in diffuse or proliferative in-stent restenosis treatment show a significant reduction (30-50%) of restenosis and major adverse cardiac events. So, without sufficient scientific proofs with active stents in this indication, curitherapy is the only validated and authorized treatment of second diffuse or proliferative in-stent restenosis.

Intracoronary radiotherapy with a 188rhenium liquid-filled PTCA balloon system in in-stent restenosis: acute and long-term angiographic results, as well as 1-year clinical follow-up

BACKGROUND

Intracoronary radiotherapy with beta- and gamma-emitters has been shown to reduce the risk of restenosis after balloon angioplasty and after coronary stenting. The present study addresses the question whether intracoronary radiotherapy using the (188)rhenium liquid-filled PTCA balloon system is feasible, safe and effective in cases of in-stent restenosis. Acute and long-term angiographic results as well as clinical events within 1 year after the procedure were evaluated.

METHODS AND RESULTS

From September 1999 to April 2000, 41 patients (mean age 60+/-10 years, 33 male, 8 female) with symptomatic in-stent restenosis underwent repeat PTCA and immediate intracoronary brachytherapy. After successful repeat PTCA (residual stenosis less than 30% in diameter), a second standard PTCA catheter was inflated with liquid (188)rhenium in the redilated in-stent restenosis for 315-880, mean 540+/-155 s with low pressure (3 atm) in order to reach 30 Gy at 0.5 mm depth of the vessel wall. In all patients with successful reintervention, intracoronary radiotherapy was unproblematically performed; in 16 patients, 21 new stents were implanted during the procedure-either immediately before or after radiation therapy. During follow-up, four episodes of stent thrombosis with subsequent myocardial infarction occurred in three patients (8 days, 37 days, 5 months and 6 months after the procedure, respectively). This complication was seen exclusively in patients with newly implanted stents. One patient of the stent group died suddenly 46 days after the procedure. All 40 surviving patients underwent repeat angiography in cases of repeat angina or routinely 6 months after brachytherapy, respectively. In the redilated target vessels without new stenting, restenosis (stenosis >50% in diameter) or reocclusion was observed in only 5 of 25 (=20%) cases, but in the restented target lesions, in 10 of 15 (=67%). Event-free survival (death, myocardial infarction, TVR) at 1 year after repeat dilatation and subsequent brachytherapy was 80% for patients not newly stented, but only 44% for patients with new stents.

CONCLUSIONS

Intracoronary radiation therapy with the liquid-filled beta-emitting (188)rhenium balloon is a safe and effective therapy in cases of in-stent restenosis. The positive effect of irradiation, however, is abolished if a new stent is needed. In the not newly stented patients, 1-year follow-up is encouraging.

Novel Approaches to Reduce Restenosis

Percutaneous coronary intervention (PCI) has become the major technique of revascularization and is replacing cardiac bypass surgery. PCI is typically performed today with a combination of balloon dilatation and stents, with some 80% of the procedures followed by stent implantation. After balloon dilatation, an acute recoil response can be responsible for some 30% immediate loss of the vessel lumen at the end of the procedure. Restenosis is the late loss (within 6-9 months) of the lumen of the artery due to vessel shrinkage (negative remodeling) and an intense proliferative response to the local injury. Stents reduce restenosis by 30% by preventing acute recoil and reducing long-term negative arterial remodeling. Yet, long-term pressure of the stent struts against the vessel wall stimulates an increased arterial proliferative response, which is the major cause for stent restenosis. Limiting the proliferative response by local radiation (brachytherapy) have reduced restenosis, at a cost of increased late thrombogenicity and delayed vessel healing. Drug-eluting stents have shown extremely promising results in limiting restenosis. Rapamycin and paclitaxel are the major drugs in eluting stents in clinical use today, having reduced restenosis to less than 10%. Local cellular and genetic therapy approaches are currently at preclinical phases. The future of percutaneous revascularization remains bright and will enhance the effectiveness of PCI as the primary revascularization therapy for coronary artery disease.

De Novo Femoropopliteal Stenoses: Endovascular Gamma Irradiation Following Angioplasty—Angiographic and Clinical Follow-up in a Prospective Randomized Controlled Trial

PURPOSE

To assess and report the follow-up results of a randomized controlled trial on centered endovascular gamma irradiation performed after percutaneous transluminal angioplasty (PTA) for de novo femoropopliteal stenoses.

MATERIALS AND METHODS

Thirty patients who underwent PTA for de novo femoropopliteal stenoses were randomly assigned to undergo 14-Gy centered endovascular irradiation (irradiation group, n = 15) or no irradiation (control group, n = 15). Intraarterial angiography was performed 6, 12, and 24 months after treatment; duplex ultrasonography (US), the day before and after PTA and 1, 3, 6, 9, 12, 18, and 24 months later. Treadmill tests and interviews were performed the day before PTA and 1, 3, 6, 9, 12, 18, and 24 months later. Results of angiography, duplex US, treadmill tests, and interviews were evaluated with the nonpaired t or the Fisher exact test.

RESULTS

Baseline characteristics did not differ significantly between the two groups. Mean absolute individual changes in degree of stenosis, compared with the degrees of stenosis shortly after PTA, in the irradiation group versus in the control group were -10.6% +/- 22.3 versus 39.6% +/- 24.6 (P <.001) at 6 months, -2.0% +/- 34.2 versus 40.6% +/- 32.6 (P =.002) at 12 months, and 7.4% +/- 43.2 versus 37.7% +/- 34.5 (P =.043) at 24 months. The rates of target lesion restenosis at 6 (P =.006) and 12 (P =.042) months were significantly lower in the irradiation group. The numbers of target lesion re-treatments were similar between the groups, but target vessel re-treatments were more frequent in the irradiation group. There were no significant differences in interview or treadmill test results between the two groups at t test analysis.

CONCLUSION

The degree of stenosis was significantly reduced 6, 12, and 24 months after angioplasty of de novo femoropopliteal stenoses in the patients who underwent endovascular irradiation.

Geographical miss during centered intracoronary beta-radiation with 90Yttrium: incidence and implications for recurrence rates after vascular brachytherapy for de novo lesions

OBJECTIVES

The authors sought to determine the incidence and causes of geographical miss (GM) and evaluate its impact on edge restenosis after 'primary', centered, intracoronary beta-radiation therapy.

BACKGROUND

Edge restenosis is a limitation of intracoronary beta-radiation therapy. GM occurs when the radiation source does not fully cover the injured segment and may account for this phenomenon.

METHODS

One hundred and eighty-one patients enrolled in the Dose-Finding study were retrospectively analyzed. The patients were randomized to receive 9, 12, 15 or 18 Gy at 1 mm tissue depth. Using quantitative coronary angiography the effective irradiated segment (EIRS) and both edges were studied prior to and after intervention, and at six-month follow-up. GM was defined as a situation where the effective radiation source length (24 mm) did not fully cover the injured segment. The edges of the EIRS that were injured during the procedure constituted the GM edges. A greater than 50% diameter stenosis at follow-up was considered significant. GM was determined by the simultaneous, electrocardiographically matched, side-by-side projection of the source and balloons in place, in identical projections surrounded by contrast.

RESULTS

In 16% of patients GM was noninterpretable owing to inadequate filming. GM constituted 21.1% of the interpretable edges and 40.1% of the interpretable vessels analyzed. The occurrence of restenosis in the EIRS and the analyzed vessel segment (VS) was similar between procedures with and without GM. In vessels with GM, restenosis was significantly increased from the EIRS to the VS (from 8.77% to 21%, p = 0.05) as opposed to non-GM vessels (from 11.9% to 19%, p = 0.6). GM tended to be associated with a greater incidence of significant stenosis at the edges of the EIRS (8.3% versus 4.0%, p = 0.15) compared with individuals with >50 % stenosis but no GM. This effect was more prominent at the distal edge. The relation of GM and edge restenosis was independent of dosage.

CONCLUSIONS

Since GM does not affect the incidence of restenosis in the EIRS, restenosis in this segment should be considered a treatment failure, probably due to inadequate dosage. GM is related to significant increase in restenosis from the EIRS to the VS. GM tends to be associated with restenosis at the edges of the EIRS. This is a local phenomenon, which is independent of dosage and which has a specific pathophysiology (combination of injury and low-dose radiation). If GM can be eliminated, the results of vascular brachytherapy will be improved.

New strategies to prevent restenosis

The Holy Grail of cardiovascular pharmacology has been the search for an effective therapy targeting restenosis after angioplasty and/or intra-arterial stenting. The failure of promising therapeutics in clinical trials underscores the complexity and redundancy of the signaling cascades regulating mitogenesis and fibrogenesis. Novel therapeutic modalities have potential to target dysfunctional signaling elements directly in vascular smooth muscle cells. Significant progress in the treatment against restenosis will require the exploitation and cross-fertilization of developments in the fields of pharmacology, bioengineering, genetics, and molecular biology. Collaboration among researchers in these fields will be essential.

Morphometric and histological changes in the vascular wall after external radiation for the prevention of intimal hyperplasia

BACKGROUND

Recent reports describe spontaneous dissections and aneurysms after coronary and peripheral artery irradiation for the prevention of intimal hyperplasia. We investigated histological changes and the vasomotor reaction in the vascular wall after external radiation for the prevention of intimal hyperplasia in rabbits.

MATERIALS AND METHODS

The aorta was experimentally injured in 34 rabbits who were then assigned to one of three groups: irradiation with 20 Gy; with 25 Gy; and a control group with no irradiation. Before the arterial injury and 45 days later, vasomotor function was assessed with an intravascular ultrasound catheter. The aorta was resected for morphometric and histological studies.

RESULTS

After injury and irradiation, vasomotor responses were significantly lower in the two irradiated groups (P < 0.05). Intimal thickness and the intima/media ratio were significantly lower in irradiated groups. In the irradiated group histological examination showed reduced intimal proliferation with an intact endothelium. In the 20-Gy irradiated group the vascular media contained necrotic areas, and in the 25-Gy irradiated group, severe fibrosis.

CONCLUSION

After arterial injury, external irradiation at 20 and 25 Gy effectively reduces aortic intimal and medial thickening. Histological changes include recasting with necrosis and fibrosis causing a decreased vasomotor response. Further investigations are needed to confirm medial necrosis and replacement with fibrosis. Because the irradiation doses in this study match those currently used and also recommended for experimental and clinical use, if confirmed in humans parietal recasting might possibly explain the reported spontaneous dissections and aneurysm formation after irradiation.

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.

Intracoronary brachytherapy for the prevention of restenosis after percutaneous coronary revascularization

PURPOSE

The purpose of this article is to review the current literature pertaining to intracoronary brachytherapy for the prevention of restenosis after percutaneous coronary revascularization (PCR).

METHODS

English-language articles were identified through a MEDLINE search (January 1984 to January 2003) using the keywords brachytherapy, radioactive stents, and coronary arteries. In addition, pertinent reference citations from relevant articles were reviewed.

RESULTS

Restenosis after PCR is a complex process, thought to be due to a combination of vessel wall remodeling and neointimal proliferation. To date, catheter-based delivery of intracoronary brachytherapy has been found to prevent vessel wall remodeling and causes a reduction in the proliferation of the neointima. Neointimal proliferation, as measured by mean neointimal area, was reduced in all animal studies (range 26%-91%). In contrast, animal studies examining radioactive stents demonstrated an increase in neointimal proliferation, suggesting that they may not be helpful at preventing post-PCR restenosis. All human studies using catheter-based intracoronary brachytherapy for in-stent restenosis have employed either beta (beta) or gamma (gamma) radiation sources with variable doses of radiation (range 7-56 Grays [Gy]). Restenosis occurred in 12% to 40% of patients in nonrandomized studies, and clinical events occurred in 13% to 50% of patients. To date, there have been 7 published randomized trials in humans comparing catheter-based intracoronary brachytherapy to placebo, with a total of 1047 patients. The dose of radiation in the trials ranged from 14 Gy to 30 Gy. During follow-up, 8% to 33% of patients who received brachytherapy had restenosis versus 39% to 64% of patients receiving placebo. Clinical events occurred in 19% to 50% among patients who received brachytherapy versus 29% to 79% among patients receiving placebo. The majority of human studies examining radioactive stents do not demonstrate a reduction in restenosis in patients post-PCR. There are no randomized trials examining radioactive stents in humans.

CONCLUSION

Nonrandomized studies of radioactive stents suggest they are not effective at preventing in-stent restenosis. In contrast, data from animal and human studies suggest that catheter-based intracoronary brachytherapy can prevent in-stent restenosis and reduce clinical events post-PCR.

Catheter based intracoronary brachytherapy leads to increased platelet activation

BACKGROUND

Vascular brachytherapy (VBT) after percutaneous coronary intervention (PCI) is associated with a higher risk of stent thrombosis than conventional treatment.

OBJECTIVE

To investigate in vivo periprocedural platelet activation with and without VBT, and to assess a possible direct effect of radiation on platelet activation.

DESIGN

Of 50 patients with stable angina, 23 received VBT after PCI, while 27 had PCI only. The 23 patients who received VBT after PCI were pretreated for one month with aspirin and clopidogrel. Platelet activation was assessed by flow cytometry.

RESULTS

The two patient groups did not differ in their platelet activation before the intervention. There was a significant increase in activation immediately after VBT, with 21.2% (interquartile range 13.0% to 37.6%) thrombospondin positive and 54.0% (42.3% to 63.6%) CD 63 positive platelets compared with 12.7% (9.8% to 14.9%) thrombospondin positive and 37.9% (33.2% to 45.2%) CD 63 positive platelets before the intervention (p < 0.001 and p < 0.01, respectively). Patients without VBT had no periprocedural difference in platelet activation immediately after PCI. No increase in platelet activation was found after ex vivo irradiation of blood samples obtained from healthy controls.

CONCLUSIONS

Catheter based intracoronary VBT carried out according to current standards is highly thrombogenic. The current antithrombotic treatment with aspirin and clopidogrel is not sufficient to suppress platelet activation during the procedure. From in vitro experiments, it appears that platelet activation during brachytherapy is not caused by irradiation but by the procedure of catheter based VBT.

A biplane angiographic study on cardiac motion of coronary artery stents: options to minimize the target volume for high-precision external beam radiotherapy of coronary artery in-stent restenosis

PURPOSE

High-precision external beam radiotherapy (EBRT) has been suggested as a potential alternative to endovascular brachytherapy for the treatment of coronary artery in-stent restenosis. The purpose of our study was to investigate and compare different options to define a smallest feasible target volume.

METHODS AND MATERIALS

The cardiac motion of 17 coronary artery stents in 17 patients was studied by use of biplane conventional angiography, recorded during breath-hold. Each stent was reconstructed in three dimensions by use of biplane sets of frames covering an entire cardiac cycle. The volume traversed by the stent during the entire or part of the cardiac cycle was determined. Four options to define the stent-traversed volume (STV) as a target for high-precision EBRT were investigated.

RESULTS

The mean STV during the entire cardiac cycle was 3.5 cm3; the STV represented less than 1% of the heart volume in all patients. The STV during the diastolic and systolic phase resulted in a mean reduction of 26.6% and 29.1%, respectively, compared with the STV during the entire cardiac cycle. The smallest STV, measured during a 160-ms interval within the cardiac cycle, resulted in a mean maximal reduction of 75.9% compared with the STV during the entire cardiac cycle.

CONCLUSIONS

The STV during the entire cardiac cycle represents a small potential target volume for high-precision EBRT. A significant reduction of this target volume is possible in case of definition during a selected interval within the cardiac cycle.

External beam ionizing radiation for inhibition of myointimal hyperplasia after dilatation and anastomoses: experimental models and results

In recent years there has been intensive research on the use of ionizing radiation for inhibition of intimal hyperplasia (IH). Results have clearly established that beta ionizing radiation delivered from an endoluminal source after angioplasty inhibits intimal restenosis. This effect has been confirmed by recent multicenter clinical trials in patients undergoing coronary dilatation. The purpose of this study was to determine if gamma radiation therapy delivered superficially from an external source also reduced smooth muscle cell proliferation in two animals models-the first involving experimentally induced restenosis and the second involving anastomosis between a prosthesis and artery. Ultimately we hope to develop a therapeutic application for patients undergoing peripheral anastomoses, especially in the lower extremities. Two different animal models were used in this two-stage study. The first-stage rabbit model (model 1) involved balloon injury of the aorta to validate the dose effect of external beam irradiation. The second-stage porcine model (model 2) involved aortic bypass followed by external beam irradiation of the distal anastomosis site. In model 1 a total of 56 rabbits were studied. They were divided into five groups including one control group in which external radiation was not applied after balloon injury and four test groups in which external radiation was applied in a single fraction on day 0 at four different doses: 10 grays, 15 grays, 20 grays, and 25 grays. In model 2, a total of 24 pigs underwent aortic bypass with a 6-mm PTFE graft followed by irradiation of the distal end-to-side anastomosis at a dose of 20 grays on day 0. In both models specimens were harvested after 6 weeks and studied histologically after staining with HES and orcein, histomorphometrically by measuring intimal hyperplasia, and immunohistochemically using actin and factor VIII/von Willebrand factor (F VIII/vWF). The zones of study on the anastomosis were separated into base of the artery to the tip and heel of the anastomosis and the edge of the arteriotomy. Measurements were compared using the Mann Whitney test. In the first-stage model designed to study IH in rabbits, mean intimal and medial thickness values and the intima-to-media ratio showed no difference between the control group and the groups irradiated at doses of 10 grays and 15 grays (p = 0.111, p = 0.405, and p = 0.14); (p = 0.301, p = 0.206, and p = 0.199). Conversely, there was a significant difference between the control group and the groups irradiated at 20 grays and 25 grays (p < 0.0001, p = 0.107 and p = 0.008; p = 0.008, p = 0.155, and p = 0.008). Histological examination demonstrated extensive changes in the wall with high-grade fibrosis after application of ionizing radiation. In the second-stage swine model, irradiation significantly inhibited development of IH at the level of anastomosis both at the base of the artery (p < 0.01) (tip 0.06 vs. 0.27 mm and heel 0.04 vs. 0.36) and at the level of the arteriotomy at the suture site (p < 0.001) (0.13 vs. 0.86 mm). Immunochemical analysis of the thickened zones showed a positive reaction of endothelial cells to smooth muscle actin and F VII/vWF. Like irradiation applied using an endoluminal source, superficial gamma ionizing radiation from an external source inhibits IH. Analysis of the dose effect showed that the overall dose must be between 15 and 20 grays. External radiation also reduces overall IH at the anastomosis between a prosthesis and artery. Although these experimental data are promising, further study will probably be necessary before attempting to undertake clinical trials using external beam radiation therapy for patients undergoing peripheral anastomoses.

Intravascular brachytherapy: indications and management of adverse events

Intravascular brachytherapy has become the standard of care for the treatment of coronary in-stent restenosis after repeat angioplasty. More than 5000 patients have been treated as part of various clinical trials. Based on the results of the GAMMA I trial, the START ((90)Sr Treatment of Angiographic Restenosis Trial), and the INHIBIT (INtimal Hyperplasia Inhibition with Beta In-stent restenosis Trial), the Checkmate system using (192)Ir, the Betacath system using (90)Sr/Y, and the Galileo system using (32)P, have been approved for the treatment of in-stent restenosis. With a better understanding and application of radiation oncology concepts to vascular brachytherapy, problems such as edge failure are being overcome. The complication of late thrombosis has also become less significant with the elimination of restenting at the brachytherapy procedure, and the prolonged use of antiplatelet therapy. There are other competing modalities in the early phases of clinical trials. The durability of results, lack of any significant long-term complications and the confirmation of the efficacy in other sites will further consolidate the role of radiation in treating in-stent restenosis.

Three-Year Clinical Follow-up Results of Intracoronary Radiation Therapy Using a Rhenium-188-Diethylene-Triamine-Penta-Acetic-Acid-Filled Balloon System

BACKGROUND

Intracoronary radiation therapy (IRT) prevents recurrent in-stent restenosis, but its long-term safety and efficacy remain uncertain. In the present study, the long-term clinical outcome of IRT using the rhenium-188 ((188)Re)-filled balloon system was evaluated.

METHODS AND RESULTS

After successful catheter-based treatment of either a de novo or restenotic lesion, 187 patients were randomly assigned to either the radiation (N=104) or the control (N=83) group. The (188)Re-filled balloon system was designed to deliver 17.6 Gy to 1.0-mm tissue depth. Angiographic restenosis was significantly reduced with IRT at 9 months (18.9% vs 45.9%, p<0.001), but the incidence of major adverse cardiac events (MACE) including death, myocardial infarction, and target-vessel revascularization (TVR) by 3 years showed no difference. Lack of clinical benefit might be related to TVR caused by geographic miss (6/22, 28.6%), balloon-induced unhealed dissection (3/22, 13.6%) and late thrombosis (2/22, 9.1%). In the restenotic subgroup (N=39), the MACE rate within 3 years was significantly reduced with IRT (14.3% vs 54.5%, p=0.01).

CONCLUSIONS

IRT using the (188)Re -filled balloon system is safe and technically feasible. Although IRT failed to show favorable outcomes for de novo lesion, the clinical benefits for restenotic lesions seem durable for 3 years. Furthermore, preventing geographic miss and dissection might improve long-term outcomes.

Prevention of intimal hyperplasia

OBJECTIVE

Endovascular brachytherapy, delivered by a variety of catheter-based devices, has proven clinically effective for the inhibition of neointimal hyperplasia (NIH) after coronary and peripheral balloon/stent angioplasty. No platform, however, has been developed to deliver low-dose radiation in concert with vascular surgical operations. The purpose of this study was to evaluate the vascular response following balloon injury to the rabbit carotid artery, with and without topical low-dose 45Ca, applied by an external vascular "wrap".

METHODS

Twelve rabbit carotid arteries were subjected to balloon injury by embolectomy catheter. The common carotid artery was then "wrapped" circumferentially with a biostable polyurethane membrane (Nanoskin Secant Medical, Perkasie, PA), without radiation (n = 6), or with radiation (n = 6) (45Ca approximately 50 microCi). The animals were sacrificed at 4 weeks for histologic assessment of the treated vessels.

RESULTS

The 45Ca wrap inhibited NIH evidenced by trends towards reduction of intimal area (0.46 +/- 0.19 control carotid vs. 0.35 +/- 0.15 (45)Ca-treated carotid arteries; P = .11), maximal intimal thickness (0.21 +/- 0.08 vs. 0.16 +/- 0.05; P = .12), average intimal thickness (0.12 +/- 0.06 vs. 0.08 +/- 0.03; P = .08), marginally significant reduction in percent area stenosis (33 +/- 15% vs. 21 +/- 9%; P = .06) and marked neointima suppression in areas immediately adjacent to 45Ca wrap remnants. Medial necrosis (P = .003), however, was observed slightly more for 45Ca-treated carotid arteries versus control arteries.

CONCLUSION

Low-dose 45Ca beta-radiation labeled onto a polyurethane membrane appears to inhibit NIH in an animal model.

[External ionizing radiation on the prosthesis-arterial anastomosis for the prevention of intimal hyperplasia and study of biomechanical resistance. Experiments and results]

PURPOSE

To evaluate the use of external ionizing radiation for the prevention of intimal hyperplasia in anastomosis between PTFE and artery.

METHODS

Bypass using a 6 mm PTFE was performed on a swine subrenal aorta with a distal conventional anastomosis (N = 35) associated (test group; N = 17) or not (control group; N = 18) with post-operative external radiation (20 Gy) on this anastomosis. At 45 days, histological studies and morphometric studies were performed on the aorta receiving the anastomosis. Two protocols were performed, the first protocol with standard analysis and the animals were randomly assigned to either group (test group; N = 11 and control group; N = 13) and the second protocol with test of extraction comparing the biomechanical resistance between the irradiated group (N = 6) and the control group (N = 5).

RESULTS

Twenty-one animals survived the procedure in the first protocol, 11 in the second. The endothelium was restored in either group. Histological recasting was observed in the media after radiation with fibrosis and areas of necrosis. Intimal thickness was significantly lower after irradiation in the heel (P < 0.01), the head (P < 0.01) and the suture line (P < 0.001) of the artery in the first protocol. The intimal thickness was also significantly lower in the second protocol after radiation in the heel (P < 0.05) and the head of the artery (P < 0.05). There was no difference between the two groups comparing the resistance.

CONCLUSION

After external irradiation, the thickness parameter of the intima decreased significantly in comparison with the control group with similar resistance. Media fibrosis and necrosis need to be confirmed by further investigation.

Inhibition of Neointimal Proliferation with188Re-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.

Coronary restenosis: a review of mechanisms and management

Percutaneous coronary interventions represent an attractive alternative to surgical revascularization; nevertheless, these techniques continue to be characterized by their propensity to elicit restenosis. Despite an exhaustive search for an effective pharmacotherapy to treat or prevent restenosis, hundreds of clinical trials have failed to identify an agent with proven therapeutic benefit. Recently, however, the Food and Drug Administration approved intracoronary radiation (brachytherapy) as a viable therapeutic option for in-stent stenosis. In addition, recent randomized trials have shown encouraging results for drug-eluting stents. This article reviews the pathophysiology of restenosis, along with current and future treatment options.

Catheter-based 32P beta-radiation after stent implantation in porcine coronary arteries: role of source-centering and geographical miss

The present study examined the role of source-centering and geographical miss in vascular brachytherapy. After implantation of 13 mm long stents, 38 coronary arteries in 13 pigs were randomly assigned to centered brachytherapy (n = 13), eccentric brachytherapy (n = 13), or no radiation (n = 12). Geographical miss was avoided by careful placement of a 27 mm (32)P beta-radiation source. Restenosis was quantified by angiography, histomorphometry, and intravascular ultrasound at 28 days. Source-centering led to a significant (P < 0.001) reduction of in-stent area stenosis (centered radiation, 12% +/- 5%; eccentric radiation, 37% +/- 21%; control arteries, 41% +/- 13%). Despite 7 mm coverage of the edge segments, radiation was found to induce edge stenosis due to neointima formation and constrictive vascular remodeling. We conclude that centered radiation was superior to eccentric radiation in reducing in-stent luminal narrowing while radiation-induced edge stenosis was still observed despite extension of the radiation zone to 7 mm beyond the stent edges.

Intracoronary β-Irradiation With Liquid Rhenium-188

STUDY OBJECTIVE

To assess the feasibility and short-term outcome of intracoronary irradiation after pure balloon angioplasty (POBA) of de novo and post-POBA restenotic lesions with a liquid beta-emitter (188)Re-filled balloon.

DESIGN AND SETTING

Nonrandomized prospective study with contemporaneous control group in a single medical center.

PATIENTS AND METHODS

In the Taiwan Radiation in Prevention of Post-Pure Balloon Angioplasty Restenosis study, 40 patients underwent 14-Gy irradiation and 15 patients underwent 20-Gy irradiation at a tissue depth of 0.5 mm after POBA. Thirty control patients received a 5-min inflation with a perfusion balloon catheter after POBA.

RESULTS

No procedural or in-hospital complications, or 30-day major adverse cardiac events were noted. Six-month angiographic restenosis rates were 49% in the 14-Gy group, 20% in the 20-Gy group, and 57% in the control group (p = 0.05, 20-Gy group vs control group). In the lesions with an arc of calcification of < 180 degrees, restenosis occurred in 15 of the 34 lesions (44%) in the 14-Gy group and in none of the 11 lesions (0%) in the 20-Gy group (p = 0.007). In a vessel with a reference diameter < 3.0 mm, restenosis occurred in 1 of the 8 lesions (13%) in the 20-Gy group, and in 8 of the 11 lesions (73%) in the control group (p = 0.02). In the post-POBA restenotic lesions, restenosis occurred in none of the six lesions (0%) in the 20-Gy group, and in five of the six lesions (83%) in the control group (p = 0.008).

CONCLUSIONS

Post-POBA, catheter-based brachytherapy in nonstented native coronary artery with a (188)Re-filled balloon can effectively reduce target lesion restenosis with 20-Gy irradiation at a tissue depth of 0.5 mm and seems to be more effective in the treatment of lesions with an arc of calcification < 180 degrees, in a vessel with a reference diameter of < 3.0 mm, and in post-POBA restenotic lesions.