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.