Intravascular brachytherapy: a review of the current vascular biology

Restenosis is a major limitation of coronary angioplasty, requiring further intervention in the majority of cases. Intracoronary radiation has been employed in recent years to prevent restenosis lesions with effective results, principally in in-stent restenosis. Restenosis is generally considered as an excessive form of normal wound healing divided up in processes: elastic recoil, neointimal hyperplasia, and negative vascular remodeling. Restenosis has previously been regarded as a proliferative process in which neointimal thickening, mediated by a cascade of inflammatory mediators and other factors, is the key factor. Data from recent studies have pointed to negative vascular remodeling as a major contributing factor. Recent studies have also identified particular cell lines that might be critical regulators of restenosis, particularly monocyte-derived macrophages and myofibroblasts. This review summarizes the current theories of vascular biology pertaining to restenosis in coronary arteries and the potential mechanisms of why radiation may effectively inhibit restenosis.

Correlates of failure following treatment with Sr-90 beta irradiation for in-stent restenosis

We sought to determine the correlates of failure following intracoronary radiation therapy (IRT) with Sr-90 using the Novoste Beta-Cath system for the treatment of in-stent restenosis (ISR) in a broad range of patients. IRT has been shown to be more efficacious compared to placebo for the treatment of ISR in large randomized trials. However, even in patients treated with IRT, major adverse cardiac events occur in approximately 20% of cases on follow-up. This trial sought to elucidate the correlates of failure following successful IRT for ISR. To determine the correlates of IRT failure, we retrospectively compared the demographics, lesion characteristics, and clinical outcomes of 102 consecutive patients with ISR treated with Sr-90 from September 1998 to July 2001. IRT failure was defined as death, myocardial infarction (MI), or target vessel revascularization (TVR) due to repeat ISR on follow-up. A comparison of the clinical and angiographic profile of IRT failures (n = 16) vs. IRT successes (n = 86) revealed that a history of smoking (75% vs. 40%; P = 0.012), current use of calcium channel blockers (84% vs. 45%; P = 0.013), ostial location of target lesion (44% vs. 16%; P = 0.020), and mean posttreatment minimal luminal diameter (MLD; 1.64 +/- 0.19 vs. 2.21 +/- 0.29 mm; P < 0.001), respectively, were correlated with failure using univariate analysis. After multivariate regression analysis, the correlates of failure that remained significant were treatment of an ostial lesion (OR = 31.2; 95% CI = 2.6-382.7; P = 0.007) and final posttreatment MLD (P < 0.001). Ostial location of target lesion and smaller posttreatment MLD are correlated with subsequent death, MI, and TVR following therapy with Sr-90 for ISR.

Mechanisms and methods to resolve edge effect

Vascular brachytherapy (VBT) has established itself as a viable modality to treat in-stent restenosis (ISR). The problems associated with VBT have been understood well and remedied. Late thrombosis has been overcome to a great extent by prolonged antiplatelet therapy. Edge effect is another important limitation of VBT and is due to inadequate radiation coverage of the edges following VBT. It may be overcome by confining injury to the lesion segment and extending the radiation sources by a few millimeters from the injured segment.

Intravascular brachytherapy for native coronary ostial in-stent restenotic lesions

OBJECTIVES

We analyzed the effects of vascular brachytherapy (VBT) on ostial in-stent restenosis (ISR).

BACKGROUND

In-stent restenosis has a high recurrence rate after percutaneous reintervention. The recurrence rate of ostial ISR lesions and the impact of VBT remain unknown.

METHODS

We evaluated 133 patients with native coronary ostial ISR from a pooled database of 990 patients enrolled in randomized VBT trials. Independent quantitative angiography was performed at baseline and follow-up in 45 gamma, 27 beta, and 61 placebo patients.

RESULTS

Binary restenosis was significantly higher in placebo than radiated patients (75.4% vs. 17.8% in gamma vs. 22.2% in beta, p < 0.0001). The treatment effect of both gamma (odds ratio [OR] 0.06; 95% confidence interval [CI] 0.02 to 0.17) and beta VBT (OR 0.10; 95% CI 0.03 to 0.31) was maintained after controlling for differences in baseline lesion length. Proximal and distal radiation edge restenosis rates were similar among the groups. Vascular brachytherapy of true aorto-ostial lesions (n = 34) was similarly beneficial: restenosis rates of placebo versus gamma or beta patients of 83.3% versus 6.7% versus 28.6%, p = 0.0002.

CONCLUSIONS

Conventional treatment of ostial ISR is associated with a recurrence rate of over 75%. Vascular brachytherapy with either gamma or beta sources results in significant and similar reductions in restenosis compared with placebo. Similar benefits after VBT prevail in true aorto-ostial lesions.

[Clinical and angiographic one-year follow-up of vascular beta-brachytherapy for coronary lesions treated by a stent with a very high risk for restenosis]

BACKGROUND

Vascular brachytherapy (VBT) has been proven to reduce restenosis rate and unwanted cardiac events in several randomized trials. Long-term data on populations at high risk for re-interventions are few. The aim of this study was to assess the acute and one-year outcome of beta-radiation in coronary in-stent restenoses with a high likelihood of recurrence.

METHODS

In 79 patients, VBT using 90Yttrium/Strontium or 32Phosphorus, was performed. Clinical and angiographic follow-up was carried out after 6 months and 1 year.

RESULTS

44.4 % of patients had three-vessel coronary artery disease and a high prevalence of cardiovascular risk factors and comorbidity. Mean lesion length was 36.8+/-18.9 mm. VBT was successful in all patients. Fractionation of VBT was necessary in 2,5 %. Acute gain of luminal diameter was 2.15+/-0.89 mm. During the hospital stay one acute myocardial infarction (AMI) not associated with VBT occurred. After 6 months loss of luminal diameter measured 0.39+/-0.47 mm, equaling a restenosis rate (RR) of 16.8 % (1 year: 0.60+/-0.56 mm, RR 33.5 %). 18.9 % of patients required revascularization of the target lesion (1 year: 29.5 %). After 6 months, all patients survived, three had an AMI after discontinuation of clopidogrel, one of them was asymptomatic (1 year: 1 cardiac death, 2 symptomatic AMI).

CONCLUSION

Beta-VBT in patients at a high risk for recurrence after angioplasty is feasible and safe. Though the clinical and angiographic results at 1 year showed some impairment as opposed to the 6-months-follow-up, they nevertheless are largely superior to those patients from historic controls not treated with VBT.

Use of restenting should be minimized with intracoronary radiation therapy for in-stent restenosis

Restenting at the time of intracoronary radiation therapy (IRT) for in-stent restenosis (ISR) potentially increases the risk of late total occlusion (LTO) of the treated vessel. Prolonged antiplatelet therapy with clopidogrel (6 months) has been shown to be effective in reducing LTO risk. The purpose of this study was to assess the impact of restenting on clinical outcomes following IRT for ISR with 6 months of clopidogrel. We retrospectively evaluated 1,275 patients with 6-months clinical follow-up who were enrolled in radiation trials for ISR using gamma- and beta-emitters conducted at Washington Hospital Center. Patients were analyzed according to whether additional stents were deployed at the time of IRT. The predominant indication for restenting was to optimize the final angiographic result in the event of tissue prolapse or to cover edge dissections. All patients received a minimum of 6 months of clopidogrel. Baseline clinical and angiographic characteristics were similar between the restented and nonrestented groups. Radiation was delivered successfully in all cases. At 6 months, patients treated with additional stents and IRT had a significantly higher rate of target vessel revascularization than patients without additional stents (24.6% vs. 18.7%; P = 0.011). Restenting caused more frequent late thrombosis, late total occlusion, and Q-wave myocardial infarction than no restenting (4.0% vs. 2.2%, P = 0.09; 6.1% vs. 4.3%, P = 0.14; and 1.9% vs. 0.4%, P = 0.009, respectively). Restenting for the treatment of ISR is associated with increased adverse events and should be avoided after intracoronary radiation therapy for in-stent restenosis, as restenting results in a higher recurrence rate and the potential for increased late total occlusion.

Intracoronary radiation therapy improves the clinical and angiographic outcomes of diffuse in-stent restenotic lesions: results of the Washington Radiation for In-Stent Restenosis Trial for Long Lesions (Long WRIST) Studies

BACKGROUND

The Washington Radiation for In-Stent Restenosis Trial for long lesions (Long WRIST) was designed to determine the safety and efficacy of vascular brachytherapy for the treatment of diffuse in-stent restenosis.

METHODS AND RESULTS

A total of 120 patients with diffuse in-stent restenosis in native coronary arteries (lesion length, 36 to 80 mm) were randomized for either radiation with 192Ir with 15 Gy at 2 mm from the source axis or placebo. After enrollment, 120 additional patients with the same inclusion criteria were treated with 192Ir with 18 Gy and included in the Long WRIST High Dose registry. Antiplatelet therapy was initially prescribed for 1 month and was extended to 6 months in the last 60 patients of the Long WRIST High Dose registry. At 6 months, the binary angiographic restenosis rate was 73%, 45%, and 38% in the placebo, 15 Gy, and 18 Gy radiated groups, respectively (P<0.05). At 1 year, the primary clinical end point of major cardiac events was 63% in the placebo group and 42% in the radiated group with 15 Gy (P<0.05). The major cardiac event rate was further reduced with 18 Gy (22%; P<0.05 versus 15 Gy). Late thrombosis was 12%, 15%, and 9% in the placebo group, 15 Gy group with 1 month of antiplatelet therapy, and 18 Gy group with 6 months of antiplatelet therapy, respectively.

CONCLUSIONS

Vascular brachytherapy with 192Ir is safe and reduces the rate of recurrent restenosis in diffuse in-stent restenosis. The efficacy of vascular brachytherapy on angiographic and clinical outcomes is enhanced with a radiation dose of 18 Gy and prolonged antiplatelet therapy.

Pilot trial of oral rapamycin for recalcitrant restenosis

BACKGROUND

Sirolimus-coated stents are a promising new therapy for restenosis. We treated a select group of patients at especially high risk for restenosis with oral sirolimus.

METHODS AND RESULTS

Patients were treated with an oral sirolimus-loading dose of 6 mg after coronary angioplasty, followed by 2 mg/d for 4 weeks. Serum electrolytes, lipid profile, renal panel, and complete blood cell count were measured at 1, 3, and 5 weeks after drug initiation. Oral sirolimus was prescribed to 22 patients who had a total of 28 lesions and were at high risk for restenosis. Of the 22 study patients, 11 (50%) discontinued oral sirolimus early because of side effects or laboratory abnormalities. Hypertriglyceridemia and leukopenia were the most frequent adverse events, occurring in 3 patients each. All adverse drug effects were reversible after discontinuation. Follow-up was obtained in 100% of patients at a mean of 9.9+/-1.8 months, ranging from 6.5 to 11.8 months. Target lesion revascularization (TLR) occurred in 15 of 28 lesions (53.6%) and 13 of 22 patients (59.1%). There was no difference in TLR for patients receiving a complete course of sirolimus (n=8; 72.7%) compared with patients who terminated treatment prematurely (n=5; 45.5%; P=NS). Clinically driven repeat cardiac catheterization was obtained in 15 (68.2%) patients; restenosis (>50% diameter stenosis at follow-up) was present in 13 (86.7%).

CONCLUSIONS

Oral sirolimus does not appear to provide benefit to patients with recalcitrant restenosis. Adverse drug effects are frequent, underscoring the importance of local drug delivery to achieve high tissue concentrations without systemic adverse drug effects.

Late thrombosis after gamma-brachytherapy

Late stent thrombosis (> 30 days after treatment) is a new phenomenon occurring after vascular brachytherapy. We report the analysis of 11 patients with late thrombosis after gamma-irradiation treatment of in-stent restenosis. All patients had in-stent restenosis and angina. Contributing factors to late thrombosis include long stents, small distal vessels, and complex lesion morphology.

[Effect on dose owing to source displacement in coronary endovascular brachytherapy]

OBJECTIVE

To investigate the effect on the dose distribution of source position displacement with the target region margin in catheter-based 192Ir line source endovascular brachytherapy.

METHOD

Dose rate distribution along longitudinal axes was estimated by the formula recommended by AAPM No.60 and No. 43.

RESULTS

In the two cases of source displacement (1.1 and 5 mm) doses of target region margin was decreased dramatically (at most 53.9% and 565.8% respectively) were compared to that of no source displacement, and the affected range was 6 mm and 9 mm respectively.

CONCLUSION

Source displacement will lead to the decrease of dose in target region margin.

A multicentre European registry of intraluminal coronary beta brachytherapy

AIMS

To assess the feasibility, safety and effectiveness of intravascular brachytherapy (VBT) in routine clinical practice.

METHODS AND RESULTS

Between April 1999 and September 2000, 1098 consecutive patients treated in 46 European centres by intraluminal irradiation using a Sr/Y(90)source train (BetaCath, Novoste, GA) were included in a registry, and follow-up data were obtained for 98.8% of them after 6.3+/-2.4 months. Eight hundred and forty (76.5%) patients were males, and mean age was 62.0+/-10.2 years. Two hundred and seventy-one (26.9%) had unstable angina, and 256 (23.5%) were diabetics. Nine hundred and thirteen lesions (77.7%) were the result of in-stent restenosis, 208 (17.7%) were de novo lesions and 48 (4.1%) non-stented restenotic lesions. Mean estimated reference diameter was 3.2+/-0.5mm and mean estimated lesion length was 19.0+/-11.8mm. The prescribed radiation dose was 18.8+/-3.2Gy. Multivessel irradiation was done in 6.2% of cases, and a new stent was implanted in 29.6% of cases. Most patients received 6 or 12 months of combined aspirin and thienopyridin treatment after the procedure. Technical success was obtained in 95.9% of treated lesions, and the in-hospital major adverse cardiac event (MACE) rate was 1.8%. At follow-up, the MACE rate was 18.7% (1.9% deaths from any cause, 2.6% AMI, 13.3% TVR by PCI and 3.3% TVR by CABG).

CONCLUSION

The major current application of VBT is the treatment of in-stent restenosis. The good results of VBT observed in recent randomized controlled trials can be reproduced in clinical practice.

Intravascular ultrasound analysis of nonstented adjacent segments in diffuse in-stent restenosis treated with radiation therapy with a rhenium-188-filled balloon

The effects of beta-radiation therapy on nonstented adjacent segments in in-stent restenosis have not been sufficiently evaluated. beta-radiation therapy for in-stent restenosis was performed with a (188)Re-MAG(3)-filled balloon. We evaluated the effects of beta-radiation therapy on nonstented adjacent segments in in-stent restenosis by intravascular ultrasound (IVUS) analysis in 50 patients who received radiation therapy vs. 9 control patients. The changes (Delta = follow-up - postintervention) of the external elastic membrane (EEM), the lumen, and other IVUS variables were compared between the segments that received radiation therapy and the control segments. The significant differences between the two groups were as follows: Delta EEM area was 0.3 mm(2) in the radiation vs. -1.0 mm(2) in the control (P = 0.005) and Delta lumen area was 0.2 mm(2) vs. -1.3 mm(2), respectively (P < 0.001). In conclusion, compared with the changes of vessel shrinkage in the control group, significant vessel enlargement occurred in the nonstented adjacent segments that received radiation therapy.

Dose finding in intracoronary brachytherapy--consequences from empirical trials

In-stent restenosis has been shown to be associated with a high recurrence rate of repetitive restenosis and remains a challenging task in interventional cardiology. Randomized, placebo-controlled trials have established that beta- as well as gamma-based vascular brachytherapy reduces the incidence of restenosis and clinical event rates following percutaneous coronary intervention (PCI) for the treatment of in-stent restenosis with focal and moderate length. Despite the number of clinical trials with impressive and convincing data, dose finding in most trials is empirical and remains an open question in this fairly new field of percutaneous interventional procedures. Current clinical trials have unequivocally demonstrated a clear dose dependency for the inhibition of intimal proliferation and a significant effectiveness for the treatment of in-stent restenosis with a dose around 20 Gy. Theoretical considerations and empirical data, however, support the need for a dose escalation with current systems to even further improve clinical results. A controlled dose escalation seems, thus, justified and is apparently not related with an increased risk of major adverse cardiac events. The current article gives an overview about theoretical considerations of dosing for intracoronary brachytherapy, presents recent data from important clinical trials in different views, and opens new perspectives for the successful treatment of in-stent restenosis.

Insights into vascular pathology after intracoronary brachytherapy

Post-angioplasty restenosis is a major limitation of interventional cardiology. A large body of evidence reveals that expression of myofibroblast activity promoters moves progressively from the neoadventitia to the neointima. Brachytherapy inhibits vascular cell activity (proliferation, migration), mitigates recruitment of intimal cells, and shows a favorable prophylactic effect on late vascular remodeling by preventing adventitial constriction at the injured site. These effects of brachytherapy are dose related. Clinical and experimental data demonstrate that restenosis is determined by the balance between arterial remodeling and intimal hyperplasia. Apparently, brachytherapy-induced positive remodeling plays the principal role in increasing the luminal diameter after PTCA and, in case of a lower dose or dose fall-off, to cause detrimental edge effects. With regard to clinical course, healing defects, endothelial dysfunction and stent-vessel wall malapposition are apparently important and possibly underestimated features of vascular pathology, since they may contribute to late thrombosis and delayed intimal hyperplasia in long-term course after intracoronary brachytherapy.

Validation of the localization of the target tissue for intracoronary brachytherapy

In a previous meta-analysis of intracoronary brachytherapy (ICBT) studies, we identified the target tissue at 0.6 to 0.7 mm tissue depth and we developed two models, describing the relationship between dose and ICBT effectiveness. The purpose of the present study was to validate the identified target tissue depth and the developed dose models, using the results of 1) two prospective animal studies with ICBT, 2) a retrospective analysis of animal studies with external beam irradiation and 3) results of recent clinical ICBT trials. ICBT effectiveness in the porcine restenosis studies was quantified as inhibition of neointima proliferation. The results of these studies were correlated with the developed dose-effectiveness model. Finally, the agreement of the restenosis rates of the recent clinical trials with the developed dose-restenosis model was tested. The porcine restenosis studies demonstrated a dose-related inhibition of neointima proliferation. The radiation effectiveness of both prospective studies and the effectiveness of the studies with external beam irradiation demonstrated the best agreement with the developed dose model at a tissue depth of 0.6 mm. Furthermore, the restenosis rates of the recent clinical ICBT studies were in concordance with the developed dose-restenosis model. In conclusion, the current study validated the localization of the target tissue for ICBT at a tissue depth of 0.6 to 0.7 mm as well as the relationship between dose and ICBT effectiveness at this depth. The data provide a rationale for setting a common dose prescription point at 0.6 to 0.7 mm tissue depth.

Serial intravascular ultrasound analysis after intracoronary beta-radiation in long in-stent restenotic lesions

In-stent restenosis (ISR) represents the major limitation of stent implantation. Treatment, although of relative technical ease, is unsatisfactory due to the high incidence of recurrent restenosis. Long ISR lesions are especially prone to restenosis. Vascular brachytherapy (VBT) has emerged as a powerful adjunct therapeutic modality to treat ISR. However, VBT may be less effective in very long, diffuse ISR lesions. The present study investigated serial changes of the extent and distribution of neointima formation after beta-radiation as assessed by intravascular ultrasound (IVUS). Following interventional procedures of long ISR in 30 patients, a 40 mm or 60 mm non-centered 90Sr/90Y seed train was used for VBT. Serial (post radiation (PR) and follow-up (FU)) quantitative coronary angiography (QCA) measurements of minimal lumen diameter (MLD) and late lumen loss (LLL) and intravascular ultrasound measurements (IVUS) of cross-sectional areas of the lumen (L-CSA), stent (S-CSA) and intimal hyperplasia (IH-CSA) were performed and compared with historic controls. LLL (0.34 +/- 0.27 mm; p = 0.196), mean decrease of L-CSA (-1.0 +/- 0.8 mm2; p = 0.024) and mean increase of IH-CSA (0.5 +/- 1.3 mm2; p = 0.038) in long ISR were comparable with previously reported results of short ISR. In conclusion the average changes of lumen and intimal hyperplasia after beta-radiation of long ISR are similar to those of short ISR.

The IST registry

Intracoronary brachytherapy has been established in Europe and the US as an evidence-based treatment of in-stent restenoses. The objective of the IST Registry is to register all patients treated in Germany with intracoronary radiation and to observe the clinical outcome for a duration of 5 years. The required set of data for each patient is kept to a minimum to encourage participation. All data are entered online. In the internet, each participating site can, at any time, check their most important parameters and compare them with those of other sites. Presently, the Novoste System is used in 58 catheter labs and the Guidant System in 16, while several sites use both. The requirements regarding radiation safety in intracoronary application of gamma radiation are very strict in Germany, so the Cordis-Gamma System is used in only one German lab. In a first analysis of 332 radiated stenoses, it was observed that late vessel occlusion could occur even after 6-month administration of clopidogrel (in addition to ASA)--without new stents being implanted within the brachytherapy session. Clopidogrel should thus be administered in addition to aspirin for at least a year. Ca. 270 patients per month receive intracoronary radiation in Germany, so the IST Registry will provide important data regarding long-term observation and a foundation for future negotiations with insurance companies potentially bearing the costs. At present, neither the physician's service nor the material costs are reimbursed. The IST Registry can furthermore be used as a comparative database regarding long-term outcome following implantation of antiproliferative-coated stents.

Examining the economic impact of restenosis: implications for the cost-effectiveness of an antiproliferative stent

Over the past decade, coronary stenting has been shown to reduce the rates of angiographic and clinical restenosis compared with conventional balloon angioplasty. Despite these improved outcomes, however, coronary stenting is still hampered by a high incidence of restenosis, with important clinical and economic consequences. Recently, the development of antiproliferative, drug-eluting stents has emerged as a promising solution for the primary prevention of restenosis. This paper summarizes the current evidence on the economic impact of coronary restenosis and explores the potential impact of introducing an antiproliferative stent on the cost-effectiveness of percutaneous coronary revascularization. A decision-analytic model based on current clinical and cost data is used to examine the potential cost-effectiveness of such stents. Although prospectively designed studies will be critical to define the true impact of drug-eluting stents on long-term survival, quality of life, and costs in a broad patient population our decision analytic model suggests that as long as these stents are reasonably priced, they may be cost saving for certain patients and cost-effective for virtually all patients undergoing PCI--at least within the U.S. healthcare system.

Dose effects of stents in intravascular brachytherapy for in-stent restenosis: a Monte Carlo calculation

PURPOSE

Intravascular brachytherapy (IVBT) has been recognized as a preferred treatment for coronary in-stent restenosis (ISR) in routine practice. Stents made of high-Z materials will inevitably perturb the dose distribution of IVBT. In this work, we have conducted a systematic study on these dose perturbations for three commercially available IVBT sources.

METHODS AND MATERIALS

The EGSnrc Monte Carlo codes were used to calculate the dose distributions for the 90Sr, 32P, and 192Ir IVBT sources with and without a metallic stent in place. The ring stent type made of different material and with different strut size, metallic surface area (MSA), and radius was studied.

RESULTS

Calculations show that dose enhancement of 5% to 20% occurs inside stent in the region close to the stent struts (luminal side) for all three sources. In the region outside stent (adventitial side), dose reduction of 5% to 20% is observed for a beta source, whereas the dose effect is negligible for the gamma source. For a given stent design, the tantalum stent yields a larger dose effect than other stents made of steel, Ti, Ni, or nitinol. It is found that the dose effect significantly depends on strut thickness, and it is strongly correlated to MSA. The MSA may be used to characterize the dose effect of a stent. Sample empiric equations to relate the dose perturbations to MSA for a given source, a stent material, and a strut thickness were derived.

CONCLUSIONS

The dose perturbations due to the presence of metallic stents were found to be significant in IVBT for ISR. The dose effects of a stent can be estimated from its MSA based on derived empiric equations. The data presented are practically useful to consider the dose effects of stents in dose evaluation/treatment planning for using IVBT to treat 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.

Intracoronary beta-radiation for the treatment of patients at very high risk for recurrence of in-stent restenosis: a single center experience

BACKGROUND

Intracoronary brachytherapy has significantly reduced the recurrence of in-stent restenosis. The aim of this study was to evaluate the feasibility, safety and efficacy of intracoronary beta-radiation in patients at very high risk for recurrence of in-stent restenosis.

METHODS

We analyzed 42 patients with 50 lesions submitted to catheter-based beta-radiation (Beta-Cath System, Novoste Corporation, Norcross, GA, USA) for in-stent restenosis. Thirty-eight lesions were at the second restenosis, 8 at the third, and 4 at the fourth; a diffuse pattern was present in 78%.

RESULTS

Balloon angioplasty was performed for 30 lesions (60%) and the cutting balloon technique for 20 (40%). In 12 lesions further 14 stents had to be deployed (28%). The delivery catheter was successfully positioned in 96% of the procedures. The mean dwell time was 179 +/- 50 s with a radiation dose ranging from 18.4 to 25.3 Gy, depending on the vessel size. A complete angiographic success without coronary dissection and without any additional stenting after radiation delivery was achieved in 86%. At follow-up (7.2 +/- 2.1 months), the overall restenosis rate was 30.4% (14 lesions). A recurrence was detected in 1/11 lesions with initial focal pattern and in 13/39 lesions with initial diffuse pattern. The restenosis rate was higher in patients in whom a geographic miss had occurred (p < 0.05 vs lesions without geographic miss) and in those in whom a new stent had been deployed (p < 0.05 vs lesions treated without a stent).

CONCLUSIONS

Brachytherapy reduces the in-stent restenosis rate in patients who are at very high risk of recurrence. The restenosis pattern, geographic miss and new stent deployment seem to be negative prognostic factors for recurrence of restenosis.

Update on radiation for restenosis

Coronary stenting is now used in most coronary interventions and reduces the restenosis rate to 20% or less. However, repeat in-stent restenosis occurs in 40%-60% of these patients. Radiation therapy, guided by intravascular ultrasound, can further reduce the incidence of repeat in-stent restenosis, and clinical trials have shown that all patient subgroups benefit from it. The mechanism appears to be reduction in neointimal hyperplasia. Studies are now evaluating use of medication with stents and radiotherapy, implantation of radiation-eluting stents, longer radiation sources to adequately cover lesions, and catheter balloons inflated with radioisotope solution. Intravascular radiation may soon be the standard of treatment for patients with in-stent restenosis and has the potential to reduce the recurrence rate to below 10%.

Relationship between neointimal regrowth and mechanism of acute lumen gain during the treatment of in-stent restenosis with or without supplementary intravascular radiation

We investigated whether neointimal regrowth is related to the mechanism of acute lumen gain during the treatment of in-stent restenosis (ISR) lesions both with and without adjunct intravascular brachytherapy. From the WRIST (Washington Radiation for In-Stent Restenosis Trial) cohort, 54 ISR patients ((192)Ir, 29; placebo, 25) were treated with nonrepeat stenting percutaneous interventions (excimer laser, rotational atherectomy, and/or balloon angioplasty) prior to (192)Ir or placebo therapy. Using Simpson's method, serial volumetric intravascular ultrasound (IVUS) analyses (pre- and posttreatment and 6-month follow-up) were analyzed to obtain stent, lumen, and intimal hyperplasia (IH) volumes that were then adjusted for stent length to create stent, lumen, and IH volume indexes. In the placebo group, the acute reduction of neointima (1.6 +/- 1.4 mm(3)/mm) was counteracted by intimal regrowth (2.1 +/- 1.7 mm(3)/mm). The amount of intimal regrowth correlated directly with the intimal reduction due to the intervention (r = 0.76; P < 0.001), but not with the amount of additional stent expansion. In the (192)Ir-treated group, intimal regrowth was significantly less than in the placebo group (-0.3 +/- 0.1 vs. 2.1 +/- 1.7 mm(3)/mm; P < 0.001) despite a similar initial intimal reduction (1.3 +/- 0.9 vs. 1.6 +/- 1.4 mm(3)/mm; P = NS). No correlation was found between intimal reduction at the time of the procedure and intimal regrowth in the (192)Ir group. In this study, neointimal regrowth following treatment of ISR lesions correlates directly with the extent of acute intimal volume reduction, but not with the extent of additional stent expansion. This relation is not seen in ISR segments treated with radiation, where intimal regrowth is substantially inhibited.

Late thrombosis: a problem solved?

Late thrombosis (angiographic total occlusion associated with an acute coronary syndrome) is a potentially life-threatening complication after intracoronary radiation therapy. This review is intended to explore the preclinical and clinical evidence for late thrombosis, to discuss the etiology, and to provide guidelines for future management. Although we have gained a greater understanding of this complex entity, further research is required in a quest to curtail late thrombosis rates.

[Endovascular brachytherapy to prevent restenosis after angioplasty]

Endovascular radiotherapy is the first effective prophylaxis of restenosis after percutaneous transluminal angioplasty (PTA) and stenting. The FDA recently approved two devices for the delivery of intracoronary radiation following coronary artery stenting. Published multicenter, double-blind, randomized trials of intracoronary radiation therapy report good results for preventing in-stent restenosis, while the data for the peripheral circulation are still inconclusive. Beta-emitters are easier applicable and probably also safer, whereas gamma-emitters have been more extensively evaluated clinically so far. Primary indication for endovascular brachytherapy are patients at high risk for restenosis, such as previous restenoses, in-stent hyperplasia, long stented segment, long PTA lesion, narrow residual vascular lumen and diabetes. Data from coronary circulation suggest a safety margin of at least 4 to 10 mm at both ends of the angioplastic segment to avoid edge restenosis. To prevent late thrombosis of the treated coronary segment, antiplatelet therapy with clopidogrel and aspirin are recommended for at least 6 months after PTA and for 12 months after a newly implanted stent. An established medication regimen after radiotherapy of peripheral arteries is still lacking.

Impact of intracoronary radiation on in-stent restenosis involving ostial lesions

The aim of this study was to compare 6-month clinical outcomes of patients with in-stent restenosis (ISR) involving the ostium treated with intracoronary radiation therapy (IRT) compared to placebo therapy, and also to nonostial lesions treated with IRT. Coronary interventions in ostial lesions have a high rate of recurrence of restenosis. The impact of IRT on ostial ISR has been inadequately characterized. We assessed patients enrolled in gamma (192-iridium) and beta (90-yttrium, 32-phosphorus) radiation trials for ISR at the Washington Hospital Center. Of patients receiving IRT, 105 (8%) patients had ostial ISR and 1,289 (92%) patients had nonostial ISR. Twenty-seven patients had ostial ISR and received placebo therapy. Baseline demographic and angiographic and procedural details were similar, except ostial IRT patients had a trend toward shorter lesions (15.4 +/- 10.8 vs. 24.1 +/- 12.2 mm; P < 0.001) and had a higher rate of saphenous vein graft disease (46% vs. 19%; P < 0.001) compared to nonostial IRT patients. At 6 months, ostial lesions treated with IRT for ISR had a reduced rate of target lesion revascularization (TLR) compared to ostial lesions treated with placebo (15% vs. 43%; P = 0.004). Outcomes at 6 months were similar for the ostial and nonostial IRT groups including TLR (15% vs. 14%; P = 0.80) and composite major adverse cardiac events (18% vs. 15%; P = 0.46). Intracoronary radiation therapy is effective for ostial in-stent restenotic lesions and should be comfortably used for this challenging anatomic location.

Vascular brachytherapy: applications in the era of drug-eluting stents

Vascular brachytherapy using beta and gamma emitters has revolutionized treatment of in-stent restenosis. We are witnessing a near-abolition of the restenosis problem for simple lesions, but the future of vascular brachytherapy depends on our success in improving efficacy and reducing complications such as late thrombosis and edge effects. Optimizing dosimetry, applying adequate radiation margins, and prolonging antiplatelet therapy should equalize brachytherapy results with those of drug-eluting stents. In this overview we examine issues related to progress and optimization of outcomes derived from the use of vascular brachytherapy. We also examine its potential to expand to other applications beyond in-stent restenosis, such as the treatment of de novo lesions and peripheral vascular disease

Histopathology of coronary in-stent restenosis following gamma brachytherapy

The histopathology of in-stent restenosis (ISR) following gamma brachytherapy is described. Such histology has not been reported previously. An 82 year old man presented with recurrent ISR three months after gamma brachytherapy to an area of ISR within a native circumflex vessel. The recurrent ISR was treated with directional coronary atherectomy; the histopathology of this directional coronary atherectomy specimen is discussed. These histopathological examinations showed abundant extracellular matrix material. Surprisingly, there was a relatively small cellular (myofibroblastic) component, with an absence of endothelial cells and little evidence of active proliferation. ISR after gamma brachytherapy may be a pathologically distinct entity.

Comparison of intracoronary gamma radiation for in-stent restenosis in saphenous vein grafts versus native coronary arteries

Intracoronary gamma radiation is effective in reducing recurrent in-stent restenosis (ISR) involving native coronary arteries. This study compares the effectiveness and safety of intracoronary gamma radiation for the treatment of ISR in saphenous vein grafts (SVGs) versus native coronary arteries. In the Washington Radiation for In-Stent restenosis Trial (WRIST) series of gamma radiation trials, 1,142 patients with ISR (230 in SVG and 912 in native coronary arteries) completed 6-month clinical follow-up. All patients underwent balloon angioplasty, atherectomy, and/or restenting. Different ribbon lengths containing 6 to 23 seeds of iridium-192 were used to cover lesion lengths <80 mm. The prescribed radiation doses were 14 or 15 Gy at 2-mm radial distance from the center of the source. Baseline demographics showed that patients with SVGs were older (65 +/- 13 vs 61 +/- 11 years, p <0.001), more likely male (79% vs 64%, p <0.001), had more multivessel coronary disease (81% vs 50%, p <0.001), and less diffuse lesions (17 +/- 10 vs 24 +/- 12 mm, p <0.001). At 6 months, event-free survival was similar for patients with SVG ISR and native coronary ISR (82% vs 84%, p = 0.35). The SVG ISR population had a low rate of late total occlusion (4.6%) and late thrombosis (3.5%). Thus, treatment of ISR with gamma radiation in SVGs had similar outcome to native coronary arteries. The use of gamma radiation for the treatment of ISR should expand to SVGs.

[Brachytherapy after coronary interventions: current state and future perspectives]

Intracoronary brachytherapy is a novel, meanwhile established therapy. It is currently the only interventional procedure which has proven to effectively reduce the restenosis rates after intervention of long and diffuse in-stent restenosis. For this indication, brachytherapy can be regarded as the current treatment of choice. Randomized studies yield promising results for bypass interventions or interventions in small vessels or diabetic patients. These findings may encourage the decision to perform a percutaneous, transluminal intervention in such high-risk patients. In clinical practice, implantation of new stents in combination with brachytherapy procedures should be avoided as far as possible. In any case, the combined antiaggregatory therapy should be conducted sufficiently long to minimize the danger of late stent thrombosis. Under this treatment, the expected thrombosis rates ar within the range of placebo-treated patients. The length of the radiation source should be sufficient to cover the entire interventional injury length to avoid recurrent edge stenosis. De novo lesions are currently not a routine indication for intracoronary brachytherapy. Although intracoronary brachytherapy may effectively reduce restenosis rates in sufficiently irradiated de novo lesion segments, de novo lesions should be treated only within the set-up of controlled studies. The current available data with a follow-up period of up to 5 years show that intracoronary brachytherapy is also in the mid-term a safe and effective therapy for the reduction of restenosis after coronary interventions.

Predictors of late cardiac events following treatment with Sr-90 beta-irradiation for instent restenosis

BACKGROUND

Intracoronary radiation therapy (IRT) with Sr-90 using the Novoste Beta-Cath system has been shown to be an effective therapy for instent restenosis (ISR), but the temporal occurrence of cardiac events and the predictors of late complications require further investigation.

METHODS

We analyzed the demographics, lesion characteristics and clinical outcomes of 138 consecutive patients with ISR treated with IRT from September 1998 to March 2002. Major adverse cardiac events (MACE) were defined as death, myocardial infarction (MI) or target vessel revascularization (TVR). Characteristics of early (< or =8 months) and late (>8 months) failures were analyzed.

RESULTS

Thirty-two (23.1%) of 138 patients had MACE on follow-up; 25% (8/32) of failures occurred late after treatment with IRT. A comparison of the clinical and angiographic profile of early and late failures using univariate analysis indicates no correlations to late failure following IRT. Duration to failure after IRT was 14.25+/-3.69 months in the late group compared to 4.63+/-2.86 months in the early group (P<.001).

CONCLUSIONS

Late MACE after IRT with Sr-90 for ISR occur beyond the traditional period for clinical restenosis in 25% of cases and are difficult to predict. Further study is warranted to identify patients at risk for the development of late complications after IRT.

Brachytherapy for refractory coronary artery restenosis

A 76-year-old female patient complained of progressive episodes of chest and left arm pain and numbness, accompanied by a burning sensation in the left breast. The symptoms were nitroglycerine-responsive and consistent with her prior angina. Cardiac history included an initial percutaneous coronary intervention and 4 subsequent occurrences of restenosis in a stented area of the left anterior descending (LAD) coronary artery. Following a fifth restenosis of the LAD, the Novoste Beta-Cath Brachytherapy System was employed following balloon dilatation of the persistent recurrence. At 10 months post-brachytherapy, angiography revealed a patent LAD with no evidence of in-stent restenosis.

Beta-radiation therapy for long lesions in native coronary vessels: a matched comparison between de novo and in-stent restenotic lesions

OBJECTIVE

The purpose of this study was to evaluate effectiveness and to compare clinical outcome of intracoronary beta-radiation to treat long lesions (>20 mm) in patients with de novo stenosis vs. patients with in-stent restenosis (ISR).

METHODS

A matched comparison of 44 patients with 63 de novo lesions and 48 patients with 63 ISR lesions (>20 mm) treated with intracoronary beta-radiation was performed.

RESULTS

Stents were implanted in 65.1% of de novo and 19% of ISR lesions (P=.001). Radiation doses delivered were 17.2+/-3.0 vs. 20.3+/-3.0 Gy at 2 mm from the source center for de novo and ISR lesions. There was no difference in the incidence of in-hospital events. Clinical follow-up at 16.4+/-6.7 months showed no difference in major adverse cardiac events (MACE) between de novo and ISR patients (27.3% vs. 25%, P=.8). Late total occlusions (LTOs) occurred in eight patients (four in each group) treated with stents at the time of radiation and after discontinuation of ticlopidine. By multivariate analysis, stent implantation was the only predictor of late occlusions (OR 8.25, 95% CI 1.73-38.46, P<.008). Restenosis rates were similar for de novo and ISR lesions (29.3% vs. 23.2%, P=.46), as well as target lesion revascularization (TLR) and target vessel revascularization (TVR) rates (22.7% vs. 22.9% and 29.5% vs. 29.2%, respectively).

CONCLUSIONS

Intracoronary beta-radiation gives comparable results when used to treat de novo or ISR lesions provided new stent implantation can be avoided. Long-term combined antiplatelet therapy is mandatory for patients who receive new stents at the time of radiation treatment.

Durable clinical benefit following Sr90 Beta irradiation therapy for in-stent restenosis in high-volume community practice

Although randomized clinical trials have demonstrated efficacy of coronary irradiation versus placebo for the treatment of in-stent restenosis (ISR), durable long-term benefit in community practice is less well defined. From January 1, 2001, through June 30, 2002, consecutive percutaneous coronary intervention (n = 3,869) were analyzed at our center with a total of 330 patients undergoing coronary irradiation for ISR (53, Ir192; 12, P32; 265 Novoste Sr90). Novoste Sr90 was successfully performed in 265 of 270 (98%) of patients attempted by 10 operators. The mean patient age was 63 years (range 35 90) with 55% male (145/265) and 45% female (120/265). ISR anatomic subsets included multi-lesion (45/265; 17%), multi-vessel (27/265; 10.0%) and saphenous vein graft (16/265; 6.0%) interventions. At a mean follow-up of 10.5 2.8 (SD) months, fifty-three (20%) of the Novoste Sr90 treated patients had returned for symptoms requiring repeat angiography. Of these, 23 patients had repeat percutaneous coronary intervention (PCI) including 2 target site revascularizations (TSR), twelve non-TSR (distinct from the radiated segment of the target vessel), and 9 non-target vessel revascularizations (TVR). Coronary artery bypass surgery was performed in 11 total patients, 4 due to TSR, and 7 due to non-TVR. Clinical TSR was 2.3% (6/265) and TVR was 6.8% (18/265). In conclusion, the Novoste SR90 Beta-Cath System for the treatment of ISR is associated with a high procedural success rate and low TSR and TVR. Revascularization in follow-up is predominantly due to progressive disease outside the radiated segment and aggressive secondary prevention, especially prolonged anti-platelet therapy, appear critical to long-term procedural success.

Intracoronary beta radiation for in-stent restenosis in a patient with percutaneously treated hypertrophic cardiomyopathy and coronary artery disease

Atherosclerotic coronary artery disease is not uncommon in elderly patients with hypertrophic cardiomyopathy. These disease entities are increasingly being treated with catheter-based techniques. We report an elderly symptomatic woman treated simultaneously with coronary angioplasty, stenting and transcoronary ablation of septal hypertrophy who developed in-stent restenosis 7 months later, and was then treated with brachytherapy. Six-month and 1-year post-brachytherapy follow-up revealed a good angiographic result and adequate symptomatic relief. This is the first report describing the feasibility and efficacy of intracoronary beta radiation in a patient with hypertrophic cardiomyopathy.

Dosimetric comparison between high-precision external beam radiotherapy and endovascular brachytherapy for coronary artery in-stent restenosis

PURPOSE

Several drawbacks of endovascular brachytherapy for the treatment of coronary artery in-stent restenosis may be addressed by high-precision external beam radiotherapy (EBRT). The dosimetric characteristics of both treatment techniques were compared.

METHODS AND MATERIALS

The traversed volume of 10 coronary artery stents during the cardiac cycle was determined by electrocardiographically gated multislice spiral CT in 10 patients. By use of this traversed volume, high-precision EBRT treatment plans were generated for stents in the left circumflex (LCx), left anterior descending (LAD), and right coronary artery (RCA). The maximum dose to the nontargeted major coronary arteries was determined and compared to similar data calculated for endovascular brachytherapy.

RESULTS

High-precision EBRT targeted at LCx stents contributed a mean maximum dose (D(max)) of 83.5% (range: 71.6-95.3%) and 16.3% to the LAD and RCA, respectively. Targeted LAD stents contributed a mean D(max) of 39.3% (range: 14.5-94.8%) and 5.2% (range: 0-13.4%) to the LCx and RCA, respectively. Targeted RCA stents contributed a mean D(max) of 6.2% (range: 0-12.4%) and 5.8% (range: 0-11.5%) to the LCx and LAD, respectively. Endovascular brachytherapy targeted at LCx stents contributed a mean D(max) of 1.7% (range: 0.7-2.7%) and 1.0% (range: 0.6-1.4%) to the LAD and RCA, respectively. Targeted LAD stents contributed a mean D(max) of 5.2% (range: 0.5-11.4%) and 0.7% (range: 0.4-1.1%) to the LCx and RCA, respectively; targeted RCA stents contributed a mean D(max) of 0.3% (range: 0.2-0.5%) and 0.2% (range: 0.1-0.3%) to the LCx and LAD, respectively.

CONCLUSIONS

Although the doses distributed throughout the heart were higher for high-precision EBRT compared to endovascular brachytherapy, they are expected to be clinically irrelevant when nontargeted major coronary arteries are not closely situated to the targeted vessel segment. These encouraging results warrant further investigation of high-precision EBRT as a potential alternative to endovascular brachytherapy for the treatment of coronary artery in-stent restenosis.

High beta and electron dose from 192Ir: implications for "gamma" intravascular brachytherapy

PURPOSE

Trains of multiple 192Ir seeds are used in many clinical trials for intravascular brachytherapy. 192Ir source is commonly considered as a gamma emitter, despite the understanding that this radionuclide also emits a wide range of electron and beta energies, with a similar range of energy. The high dose from betas and electrons in the submillimeter range due to unsealed ends of seed sources should be precisely quantified to fully understand the backdrop for complications associated with 192Ir coronary artery brachytherapy.

METHODS AND MATERIALS

Monte Carlo simulations (MCNP4C code) were performed for a model 5-seed 192Ir train used in SCRIPPS, GAMMA, and the Washington Radiation for In-Stent Restenosis (WRIST) randomized clinical trials. A stack of radiochromic films was also used to measure the dose distributions for an actual 6-seed train.

RESULTS

In the submillimeter range very close to the source, Monte Carlo results show that betas and electrons deposit a higher dose than 192Ir photons (gamma and X-rays) over the interseed gap. A high luminal dose from the combined effects of betas, electrons, and photons emitted from 192Ir can be deposited, particularly between seeds. When prescribing 15 Gy at 2 mm, the combined dose can be as high as 160 Gy at 0.5 mm. Different peak doses near the interseed gaps were noted, which may be due to variability of seed-end surfaces and nonuniformity of seed activity within a real multiseed train. Dose-volume histograms (DVH) of lumen surfaces were evaluated for an eccentric seed train. The DVH parameters indicating the extent of hot spots in the lumen wall, DV(10), DV(5), DV(2), and DV(1) (dose received by 10, 5, 2, 1% respectively of the total lumen surface), can be as high as 55, 76, 81, and 155 Gy for a lumen with 3-mm diameter, and 75, 80, 110, and 158 Gy for a narrow 2-mm lumen.

CONCLUSION

192Ir multiple seed trains used in the SCRIPPS, GAMMA, and WRIST trials can deposit a very high dose to the luminal wall. A particularly high electron and beta dose can be delivered near the interseed gap if the source is not centered in the catheter and lumen. The dose from 192Ir betas and electrons may partially explain adverse outcomes reported from 192Ir multiseed clinical trials. Improvement of the encapsulation design to filter out the betas and electrons should be seriously considered.