[Edge effect and late thrombosis -- inevitable complications of vascular brachytherapy?]

Restenosis is the limiting entity after percutaneous coronary angioplasty. Vascular brachytherapy for the treatment of in-stent restenosis has been shown to reduce the repeat restenosis rate and the incidence of major adverse events in several randomized trials. Besides the beneficial effects, brachytherapy yielded some unwanted side effects. The development of new stenoses at the edges of the target lesion treated with radiation is termed edge effect. It occurs after afterloading brachytherapy as well as after implantation of radioactive stents. It is characterized by extensive intimal hyperplasia and negative remodeling. As contributing factors the axial dose fall-off, inherent to all radioactive sources, and the application of vessel wall trauma by angioplasty have been identified. The combination of both factors, by insufficient overlap of the radiation length over the injured vessel segment, has been referred to as geographic miss. It has been shown to be associated with a very high incidence of the edge effect. Avoidance of geographic miss is strongly recommended in vascular brachytherapy procedures. Late thrombosis after vascular brachytherapy is of multifactorial origin. It comprises platelet recruitment, fibrin deposition, disturbed vasomotion, non-healing dissection and stent malapposition predisposing to turbulent blood flow. The strongest predictors for late thrombosis are premature discontinuation of antiplatelet therapy and implantation of new stents during the brachytherapy procedure. With a consequent and prolonged antiplatelet therapy, the incidence of late thrombosis has been reduced to placebo levels. Edge effect and late thrombosis represent unwanted side effects of vascular brachytherapy. By means of a thorough treatment planning and prolonged antiplatelet therapy their incidences can be largely reduced. With regard to the very favorable net effect, they do not constitute relevant limitations of vascular brachytherapy.

Long-term outcome of patients treated with repeat percutaneous coronary intervention after failure of gamma-brachytherapy for the treatment of in-stent restenosis

BACKGROUND

Although (192)Ir intracoronary brachytherapy has been demonstrated to dramatically reduce the recurrence of in-stent restenosis, up to 24% of these patients will still require repeat target-vessel revascularization. The short- and long-term outcomes of repeat percutaneous intervention in this population have not been characterized.

METHODS AND RESULTS

Analysis was performed of all patients enrolled in the GAMMA-I and GAMMA-II brachytherapy trials who underwent repeat percutaneous target lesion revascularization (TLR) because of restenosis. Subjects were divided into 2 cohorts: those who had received (192)Ir brachytherapy and those randomized to placebo. Forty-five (17.6%) of a total of 256 patients whose index treatment was intracoronary radiation therapy and 36 (29.8%) of 121 patients whose index treatment was placebo required repeat percutaneous TLR. The mean time to this first TLR was 295+/-206 days in the irradiated group and 202+/-167 days in the placebo group (P=0.03). Acute procedural success occurred in 100% of irradiated patients and 94% of placebo controls (P=0.19). After the first TLR, a subsequent TLR was required in 15 (33.3%) of 45 brachytherapy patients versus 17 (47.2%) of 36 placebo failure patients (P=0.26). There was no significant difference in time to second TLR between the 2 groups. Other long-term major adverse event rates in both groups were comparable to those of other contemporary angioplasty/stenting series.

CONCLUSIONS

In those patients who "fail" (192)Ir intracoronary brachytherapy for in-stent restenosis, treatment with (192)Ir delays the time to first TLR. Additionally, repeat percutaneous intervention in these patients is safe and efficacious in the short term, with acceptable long-term results.

Delivered dose and vascular response after beta-radiation for in-stent restenosis: retrospective dosimetry and volumetric intravascular ultrasound analysis

BACKGROUND

Observations from previous intracoronary radiation therapy trials noted a considerable discrepancy between the prescribed radiation dose and the dose actually delivered. The aims of this study were to investigate the effect of actual delivered dose on vascular changes and to test the appropriateness of the current dose prescription.

METHODS AND RESULTS

Serial volumetric intravascular ultrasound (IVUS) analysis was performed in 30 in-stent restenosis cases treated with a 40-mm (90)Sr/Y source train. The fixed dose was prescribed at 2 mm from the centerline of the source train (18.4 Gy at 2 mm for reference diameter < or =3.35 mm and 23 Gy for diameter > or =3.36 mm). Only stent segments with full radiation coverage and device injury were enrolled and divided into 2-mm-long subsegments (n=202). D(S90)EEM (the minimum dose absorbed by 90% of the external elastic membrane surface) was calculated as the delivered dose corresponding to each segment, assuming that the radiation catheter occupied the same position in the vessel as the IVUS catheter. Mean D(S90)EEM of 23.5+/-5.82 Gy (range 12.3 to 41.7 Gy) was delivered to these subsegments. Overall, intimal hyperplasia volume remained constant from postintervention to follow-up (2.23+/-1.10 to 2.32+/-1.09 mm3/m; P=NS). Regression analysis revealed there was no correlation between delivered dose intensity and changes in intimal hyperplasia volume. No particular dose-dependent complications were appreciated in this delivered dose range.

CONCLUSIONS

The current dose-prescription protocol of (90)Sr/Y radiation to native in-stent restenosis lesions may provide substantial inhibition of neointimal reproliferation regardless of the actual delivered dose intensity.

How to fix the edge effect of catheter-based radiation therapy in stented arteries

BACKGROUND

Edge stenosis remains a serious limitation of catheter-based vascular brachytherapy (VBT). This study aims to identify the mechanisms and evaluate strategies to minimize edge restenosis in patients treated with VBT.

METHODS AND RESULTS

Thirty-four porcine stented coronary arteries were irradiated (doses of 15 or 22 Gy) with (192)Ir trains of either 6 seeds (23 mm) with 0 mm coverage at the distal stent edge and 10 mm at the proximal stent edge or 14 seeds (55 mm) centered at the distal edge of the stent with 27.5 and 14.5 mm coverage at the distal and proximal edges, respectively. After VBT, an additional 13-mm stent was positioned overlapping the distal margin of the first stent. Animals were killed at 28 days, and arteries were analyzed. Longer radiation margins were associated with reduced intimal area (IA) at the stent edge: 2.3+/-0.9, 3.6+/-2.0, and 5.3+/-2.2 mm(2) with 15 Gy for a radiation margin of 14.5, 10, and -13 mm (-13 versus 10, P=0.06; 10 versus 14.5, P=0.06). Additional stenting was associated with an increase of IA: 4.0+/-2.3 mm(2) at the overlapped segment. Increasing the dose to 22 Gy resulted in a reduction of the IA at the overlap segment to 1.31+/-0.57 mm(2) with 14 seeds (27.5 mm coverage) but was not helpful with 6 seeds (0 mm coverage): IA, 5.56+/-2.28 mm(2).

CONCLUSIONS

Extending the radiation margins to 14.5 mm from each end of the stent minimized the edge-effect phenomenon. A higher dose is essential to eliminate further increases in IA at the overlapped segment with additional stents.

A novel measurement technique to assess the effects of coronary brachytherapy in clinical trials

This paper presents a novel measurement technique to assess the effects of coronary brachytherapy. This new technique is based upon the conventional quantitative coronary analysis (QCA) technique, which is accepted worldwide as an accurate and reliable analysis tool for clinical trials. This paper provides the definitions and main issues important for correct brachytherapy analysis. Based on these definitions, this novel technique is implemented as an extension of conventional QCA software, as a multisegmental analysis tool. It allows to follow the influence of radiation on restenosis, and the mutual relation between intervention devices. A pilot interobserver study was performed to assess the reliability and reproducibility of the brachytherapy analysis tool, using 15 patient cases. The validation results show that the segment lengths, minimum lumen diameter, and reference diameters of the user-defined and derived (sub)segments can be assessed reproducible. However, these good results can only be obtained, when strict and extensive image acquisition and image analysis protocols are followed. From this pilot validation study presented in this paper and only based on a small number of patients, we may conclude that the software can be applied to clinical trials.

[Intracoronary brachytherapy--an update]

Restenosis following angioplasty represents a major clinical problem in the field of percutaneous coronary interventions. Intravascular brachytherapy reduces risk of restenosis following percutaneous interventions of native lesions and in-stent restenosis up to 50%-60%. This effect can be shown for at least one to two years. This novel therapeutic strategy is limited by a higher rate of target vessel reinterventions, and late coronary thrombosis, when platelet inhibiting drugs has been withdrawn or after implantation of multiple stents. Currently, intracoronary brachytherapy is mainly considered for treatment of in-stent-restenosis.

Interventional nuclear medicine in the prevention of restenosis following angioplasty

Restenosis is an unsolved clinical and economic limitation of angioplasty. Local irradiation is a new concept to overcome this problem. The magnitude of this health problem becomes apparent when one recognizes that 166132 percutaneous transluminal coronary angioplasty (PTCA) procedures were performed in Germany in 1999. Each angioplasty has subsequent costs of 6384 DM, which can be reduced to 2161 DM by 50% restenosis reduction due to irradiation [1]. The number of diagnostic and therapeutic procedures is growing by at least 10% per year.

Practical aspects of intra-arterial brachytherapy

A wealth of experience exists in brachytherapy delivered in a variety of methods. Both beta and gamma sources have been used in the form of wires, pellets and liquids introduced through specially designed catheters. In addition, stents have been used and work with radioactive gases proposed. A significant issue in such interventional work is dosimetry. Presently, many methods and systems are still under development undergoing clinical trials and refinement. There is considerable uncertainty in the determination of appropriate target volumes and dose prescriptions. It is not known whether treatment of only the lumen wall is sufficient, or whether the media and adventitia must also be irradiated. Clinical trials suggest success depends on delivering adequate dose to target tissues (8-20 Gy) while limiting normal tissue dose to 30-40 Gy. Some trials indicate that a mimimal dose of 8-10 Gy has to be given to the whole media and the upper limit is determined by the tolerance of the intima (localized doses of approximately 90 Gy have been applied without complications). The requirements for the source for endovascular brachytherapy and the small lumen diameters involved compound the problems of achieving accurate dosimetry. Discussion of the aspects of radiation physics and the sources of dosimetric uncertainty together with the methodology used to calculate the dose is presented.

Cost-effectiveness of gamma radiation for treatment of in-stent restenosis: results from the Gamma-1 trial

BACKGROUND

Recently, several randomized trials have demonstrated that intracoronary brachytherapy can reduce the rates of both angiographic and clinical restenosis in patients undergoing percutaneous coronary intervention (PCI) for in-stent restenosis. Whether this practice is cost-effective is unknown.

METHODS AND RESULTS

Between December 1997 and July 1998, 252 patients with in-stent restenosis were randomized to receive brachytherapy or placebo after successful PCI as part of the Gamma-1 trial. We collected detailed resource utilization and cost data for each patient's initial hospitalization and for 1 year after randomization. Compared with conventional treatment, intracoronary brachytherapy increased procedure duration, physician services, and equipment costs. As a result, initial costs were increased by nearly $4100 per patient ($15 724 versus $11 675, P<0.001). Over the 1-year follow-up period, brachytherapy reduced the need for repeat revascularization by 21% and reduced the need for bypass surgery by 44%. Although follow-up medical care costs were $2200/patient lower with brachytherapy, total costs remained higher at 1 year ($28 543 versus $26 737, P=0.46). In a sensitivity analysis that incorporated recent technical modifications and the use of prolonged antiplatelet therapy to prevent late thrombotic occlusion, follow-up cost savings increased to $3600/patient, and 1-year costs were slightly lower with brachytherapy ($26 352 versus $26 729, P=0.87). Subgroup analysis demonstrated significant cost savings in patients with diabetes and patients who did not undergo repeat stenting.

CONCLUSIONS

As performed in the Gamma-1 trial, coronary brachytherapy for in-stent restenosis improved clinical outcomes but increased 1-year costs compared with standard therapy. If late thrombosis can be eliminated, however, this technology has the potential to reduce overall medical care costs.

Elderly patients have a favorable outcome after intracoronary radiation for in-stent restenosis

Intracoronary radiation therapy (IRT) reduces recurrent in-stent restenosis (ISR) by inhibition of smooth muscle cell proliferation. The ability of these cells to replicate is limited with age due to changes in the telomeres. The purpose of this study was to assess the effect of age on outcomes following IRT for ISR. We evaluated 1,088 patients with 6-month clinical follow-up who were enrolled in radiation trials for ISR using gamma- and beta-emitters. Patients were analyzed within and between IRT (n = 861) or placebo therapy (n = 227) in four age groups (< 55, 55-65, 66-75, > 75 years). Baseline characteristics were similar within each age group of IRT patients, except elderly patients (> 75 years) had a lower rate of diabetes (28% in patients > 75 years; P = 0.008) and a higher rate of previous CABG (59% in patients > 75 years; P < 0.001). The rate of target lesion revascularization (TLR) was reduced in the elderly. TLR at 6 months was 18% in patients < 55 years, 21% in 55-65 years, 12% in 66-75 years, and 10% in patients > 75 (P = 0.009). The MACE rate at 6 months was 21% in patients < 55 years, 29% in 55-65 years, 26% in 66-75 years, and 17% in patients > 75 (P = 0.03). No effect of age was seen in placebo patients. IRT-treated patients had reduced MACE compared to placebo in all age groups, driven by reduced target vessel revascularization. Age was an independent predictor of MACE at 6 months (OR = 0.8; CI = 0.70-0.93; P = 0.004). Angiographic restenosis was not clearly associated with need for TLR in patients > 75 years. In elderly patients (> 75 years) treated with IRT for ISR, the rate of TLR was significantly reduced compared to younger patients. However, this reduction in TLR was not associated with a reduction in angiographic restenosis, suggesting that TLR should not be used as a surrogate for angiographic evaluation.

Clinical beta radiation dosimetry for brachytherapy in terms of absorbed dose to water: ISO new work item proposal for international standardization

PURPOSE

Beta radiation has found increasing interest in intravascular brachytherapy for successfully overcoming the severe problem of restenosis after interventional treatment of arterial stenosis. Prior to initiating procedures applying beta radiation there is a common need to specify methods for the determination and specification of the absorbed dose to water or tissue and their spatial distributions. The DIN-NAR standardization in radiology task group Dosimetry has initiated an international ad hoc working group for an ISO new work item proposal on the standardization of procedures in clinical beta radiation dosimetry.

METHODS

The intent of this standard is to review methods and to give recommendations for the calibration of therapeutic beta sources, a code of practice for clinical beta radiation dosimetry and guidance for estimating the uncertainty of the absorbed dose to water delivered. The standard will be confined to "scaled" radioactive sources such as single seeds, source trains, line, shell and volume sources for which only the beta radiation emitted is of therapeutic relevance. The topics will include dosimetric quantities; source data; calibration and traceability; general principles and requirements for absorbed dose measurements; in phantom dosimetry; theoretical modeling; presentation of dose distributions; clinical dosimetry; clinical quality control; irradiation treatment planning; as well as uncertainties. The document is geared to organizations wishing to establish reference methods in dosimetry aiming at clinical demands for appropriate small measurement uncertainties. Existing normative documents as well as international recommendations, such as those from AAPM, DGMP, ESTRO, NCS, ICRU, or IAEA will be taken into account.

RESULTS

The first meetings of the new international working group took place in March and September 2002 at Essen, Germany [IAEA-cn-96-73, 2002].

CONCLUSIONS

Based on the DGMP Report 16, the AAPM TG 60 up-date draft, other recommendations and normative documents, the DIN-NAR project has collected and prepared detailed material on the calibration and dosimetry of beta radiation brachytherapy sources in terms of absorbed dose to water. The ISO new work item proposal will be completed in spring 2003.

Clinical trials of intracoronary gamma radiation therapy for in-stent restenosis

The only gamma emitter used in clinical trials for in-stent restenosis is 192Iridium (192Ir). The efficacy of intracoronary gamma radiation therapy in reducing clinical and angiographic restenosis in patients with in-stent restenosis has been established. This review is intended to give an overview of the clinical trials utilizing gamma vascular brachytherapy in patients with in-stent restenosis and give insight into the future of intracoronary radiation therapy.

Vascular in situ activation radiation therapy insitustent dosimetry

PURPOSE

To investigate the radiation dosimetry of a stable stent following activation by a linac photon beam.

METHODS AND MATERIALS

A computer simulation is used in conjunction with neutron measurements to study the dosimetry of a stent activated by a linac photon beam. Two models are investigated. A gamma emitter, Model G108, with no half-life and 1.43 MeV average energy, and a beta emitter, Model D108, with 2.33 h half-life and 0.45 MeV average energy.

RESULTS

Model D108 delivers a dose exceeding 1 Gy to the artery wall when exposed to an 18-MV photon beam. Model G108 requires a 25-MV photon beam to deliver a similar dose under the same conditions of irradiation.

CONCLUSION

The very short to no half-life of InSituStent emissions makes the fractionation of the dose delivery possible. In addition, an InSituStent coated with an immunosuppressant drug may give patients the potential benefit of a combined radiation and drug treatments.

Routine intracoronary beta-irradiation. Acute and one year outcome in patients at high risk for recurrence of stenosis

AIMS

Intracoronary radiation is a promising therapy potentially reducing restenosis following catheter-based interventions. Currently, only limited data on this treatment are available. The feasibility and outcome in daily routine practice, however, is unknown.

METHODS AND RESULTS

In 100 consecutive patients, intracoronary beta-radiation was performed with a (90)Strontium system (Novoste Beta-Cathtrade mark) following angioplasty. Predominantly complex (73% type B2 and C) and long lesions (length 24.3+/-15.3 mm) were included (37% de novo, 19% restenotic and 44% in-stent restenotic lesions). Radiation success was 100%. Mean prescribed dose was 19.8+/-2.5 Gy. A pullback procedure was performed in 19% lesions. Geographic miss occurred in 8% lesions. Periprocedural thrombus formation occurred in four lesions, dissection in nine lesions. During hospital stay, no death, acute myocardial infarction, or repeat revascularization was observed. Major adverse cardiac events occurred predominantly between 6 and 12 months after the index procedure with major adverse cardiac event-free survival of 66% at 12 months (one death, 10 Q-wave myocardial infarctions, 23 target vessel revascularizations; ranked for worst event).

CONCLUSION

Routine catheter-based intracoronary beta-radiation therapy after angioplasty is safe and feasible with a high acute procedural success. The clinical 1-year follow-up showed delayed occurrence of major adverse cardiac events between 6 and 12 months after the index procedure.

The effect of intracoronary radiation for the treatment of recurrent in-stent restenosis in patients with diabetes mellitus

OBJECTIVES

The purpose of this study was to examine the effect of intracoronary radiation therapy (IRT) in diabetic patients with in-stent restenosis (ISR).

BACKGROUND

Diabetic patients are at an increased risk for restenosis, repeat revascularization procedures and late mortality after percutaneous coronary interventions and stenting. Intracoronary radiation therapy, utilizing both gamma and beta-emitters, has been shown to reduce the rate of ISR.

METHODS

The study group consisted of 749 consecutive patients with ISR who were treated with either IRT or placebo in randomized trials and registries at our center. Diabetic patients (252 radiation and 51 placebo) were compared with nondiabetic patients (371 radiation and 75 placebo).

RESULTS

In-hospital outcomes were similar between diabetic and nondiabetic patients treated with and without radiation. At six-month clinical and angiographic follow-up, there was a significant reduction in the binary restenosis (63.8% vs. 15.7%, p < 0.0001), target lesion revascularization (66.7% vs. 17.6%, p < 0.0001) and target vessel revascularization (TVR) (70.6% vs. 22.9%, p < 0.0001) rates in diabetic patients treated with radiation compared to placebo. Comparisons between the placebo arms detected a trend towards higher restenosis (63.8% vs. 48.4% p = 0.13) and TVR (70.6% vs. 56.0%, p = 0.14) in diabetic versus nondiabetic patients. In contrast, diabetic and nondiabetic patients treated with IRT experienced similar restenosis (15.6% vs. 10.7% p = 0.33) and TVR (22.9% vs. 28.2% p = 0.41) rates.

CONCLUSIONS

In diabetic patients with ISR, intracoronary radiation significantly reduced the recurrence of ISR compared to placebo. Additionally, similar rates of restenosis and revascularization procedures were achieved in irradiated diabetic and nondiabetic patients. In view of these results, IRT should be considered as a valuable therapeutic alternative in all diabetic patients with ISR.

Dose heterogeneity may not affect the neointimal proliferation after gamma radiation for in-stent restenosis: a volumetric intravascular ultrasound dosimetric study

OBJECTIVES

The goal of this study was to use serial (postirradiation and follow-up) volumetric intravascular ultrasound (IVUS): 1) to evaluate the actual distribution of gamma radiation in human in-stent restenosis (ISR) lesions, and 2) to analyze the relationship between neointimal regrowth and the delivered radiation dose.

BACKGROUND

The relationship between the neointimal regrowth and delivered dose during the treatment of ISR remains unknown.

METHODS

We analyzed 20 actively (gamma emitter) treated, native artery ISR patients from the Washington Radiation for In-Stent restenosis Trial (WRIST) that met the following criteria: on both postirradiation and six-month follow-up IVUS imaging, > or =80% of the external elastic membrane circumference could be identified throughout the treated length including the lesion and proximal and distal reference segments. Intravascular ultrasound images were digitized every 1 mm. Proximal and distal reference and stented segment luminal and adventitial contours were imported and reconstructed. The source was placed circumferentially at the site of the IVUS catheter and longitudinally according to the relationship between the radioactive seeds and stent edges. Using Monte Carlo simulations, dose volume histograms for the adventitia and intima were calculated. The relationship between the neointimal regrowth and calculated doses were evaluated.

RESULTS

There was large dose heterogeneity at both the intimal and adventitial levels. Most of the sites (93%) received >4 Gy at the adventitia, and all of the sites received >4 Gy at the intima. There was no relationship between neointimal regrowth and radiation dose.

CONCLUSIONS

Although there may be large dose heterogeneity, gamma irradiation (using a fixed dose prescription) appears to deliver a sufficient dose to prevent neointimal regrowth.

Five-year clinical follow-up after intracoronary radiation: results of a randomized clinical trial

BACKGROUND

Several clinical trials indicate that intracoronary radiation is safe and effective for treatment of restenotic coronary arteries. We previously reported 6-month and 3-year clinical and angiographic follow-up demonstrating significant decreases in target lesion revascularization (TLR) and angiographic restenosis after gamma radiation of restenotic lesions. The objective of this study was to document the clinical outcome 5 years after treatment of restenotic coronary arteries with catheter-based iridium-192 (192Ir).

METHODS AND RESULTS

A double-blind, randomized trail compared 192Ir to placebo sources in patients with restenosis after coronary angioplasty. Over a 9-month period, 55 patients were enrolled; 26 were randomized to 192Ir and 29 to placebo. At 5-year follow-up, TLR was significantly lower in the 192Ir group (23.1% versus 48.3%; P=0.05). There were 2 TLRs between years 3 and 5 in patients in the 192Ir group and none in patients in the placebo group. The 5-year event-free survival rate (freedom from death, myocardial infarction, or TLR) was greater in 192Ir-treated patients (61.5% versus 34.5%; P=0.02).

CONCLUSIONS

Despite apparent mitigation of efficacy over time, there remains a significant reduction in TLR at 5 years and an improvement in event-free survival in patients treated with intracoronary 192Ir. The early clinical benefits after intracoronary gamma radiation with 192Ir seem durable at 5-year clinical follow-up.

Intracoronary brachytherapy

Patients presenting with in-stent restenosis have an increased risk of need for repeat intervention. Intracoronary brachytherapy is indicated for these patients to prevent recurrent in-stent restenosis. Three intravascular brachytherapy systems are currently FDA-approved for use in patients: one utilizing gamma-radiation (Cordis) and two using beta-radiation (Novoste and Guidant). Current evidence and labeling do not support using intracoronary brachytherapy for prevention of restenosis in de novo lesions. Brachytherapy is absolutely contraindicated in patients unable to take prolonged combination antiplatelet drugs. Aspirin and a thienopyridine should be taken for 6 months if no new stent is placed and 12 months if a new stent is placed. If possible, new stent implementation should be avoided.

[Antiproliferative coated stents and intracoronary brachytherapy: common traits and differences]

Intracoronary brachytherapy is the first internationally recognized, evidence-based coronary intervention for in-stent restenosis. But the present and future role of brachytherapy is questioned by the first results of clinical trials with antiproliferative coated stents. This overview compares the status quo of both methods, concluding first practical considerations.

Intravascular gamma radiation for in-stent restenosis in saphenous-vein bypass grafts

BACKGROUND

Intracoronary radiation therapy is effective in reducing the recurrence of in-stent stenosis in native coronary arteries. We examined the effects of intravascular gamma radiation in patients with in-stent restenosis of saphenous-vein bypass grafts.

METHODS

A total of 120 patients with in-stent restenosis in saphenous-vein grafts, the majority of whom had diffuse lesions, underwent balloon angioplasty, atherectomy, additional stenting, or a combination of these procedures. If the intervention was successful, the patients were randomly assigned in a double-blind fashion to intravascular treatment with a ribbon containing either iridium-192 or nonradioactive seeds. The prescribed dose, delivered at a distance of 2 mm from the source, was 14 to 15 Gy in vessels that were 2.5 to 4.0 mm in diameter and 18 Gy in vessels with a diameter that exceeded 4.0 mm. The primary end points were death from cardiac causes, Q-wave myocardial infarction, revascularization of the target vessel, and a composite of these events at 12 months.

RESULTS

Revascularization and radiation therapy were successfully accomplished in all patients. At six months, the restenosis rate was lower in the 60 patients assigned to the iridium-192 group than in the 60 assigned to the placebo group (21 percent vs. 44 percent, P=0.005). At 12 months, the rate of revascularization of the target lesion was 70 percent lower in the iridium-192 group than in the placebo group (17 percent vs. 57 percent, P<0.001), and the rate of major cardiac events was 49 percent lower (32 percent vs. 63 percent, P<0.001).

CONCLUSIONS

The results of our study support the use of gamma-radiation therapy for the treatment of in-stent restenosis in patients with bypass grafts.

The impact of lesion length and reference vessel diameter on angiographic restenosis and target vessel revascularization in treating in-stent restenosis with radiation

OBJECTIVES

The study assessed the influence of lesion length and reference vessel diameter (RVD) on recurrent restenosis after gamma intracoronary radiation therapy (ICRT) for in-stent restenosis (IRS).

BACKGROUND

Intracoronary radiation therapy reduces angiographic and clinical restenosis in patients with ISR. The impact of ICRT on challenging subgroups, such as long lesions and small vessels, has not been established.

METHODS

Six-month quantitative coronary angiography and clinical follow-up were conducted to evaluate the influence of lesion length and RVD in patients with ISR treated with ICRT who were enrolled in gamma radiation trials. Angiographic binary restenosis (>50% diameter stenosis) and clinical events were assessed in 311 patients treated with gamma ICRT and 105 patients who received placebo.

RESULTS

Baseline demographic, angiographic and procedural details were similar in the two treatment groups. The ICRT group had reduced binary restenosis in vessels of all sizes (30% vs. 66%, p < 0.001), with the most benefit seen in small vessels. A trend toward reduced restenosis with ICRT was found across all lesion lengths. At six months, major adverse cardiac events (MACE) were reduced in the ICRT group compared to placebo (34% vs. 71%, p < 0.0001), driven by reduced target vessel revascularization (27% vs. 71%, p < 0.0001). The independent predictors of angiographic restenosis include ICRT (OR [odds ratio] 0.16; CI [confidence interval] 0.10 to 0.28, p < 0.001), lesion length (OR 1.03; CI 1.01 to 1.05, p = 0.004) and RVD (OR 0.40; CI 0.23 to 0.67, p < 0.001).

CONCLUSIONS

Intracoronary radiation therapy, compared to placebo, results in a significant reduction of angiographic restenosis across all vessel sizes, with a trend toward reduction of angiographic restenosis across all lesion lengths; this effect is seen predominantly in small vessels and diffuse lesions.

Clinical and angiographic outcomes after use of 90Strontium/90Yttrium beta radiation for the treatment of in-stent restenosis: results from the Stents and Radiation Therapy 40 (START 40) registry

PURPOSE

To evaluate the safety and efficacy of a 40-mm 90Strontium/90Yttrium source train in the management of in-stent restenosis within native coronary arteries.

MATERIALS AND METHODS

This multicenter, prospective registry was designed to compare the results of patients with in-stent restenosis treated with a 40-mm source train to the placebo arm of the previously reported randomized Stents and Radiation Trial (START). All patients entered in the registry were treated with repeat balloon angioplasty followed by intravascular brachytherapy. Radiation dose was prescribed based on vessel size. 18 Gy was delivered at 2 mm for vessel diameters between 2.75 and 3.35 mm, and 23 Gy was used for vessels between 3.36 and 4.0 mm. The efficacy endpoints for the START 40 registry included a reduction in the target lesion revascularization (TLR) rate, target vessel revascularization rates, and target vessel failure (TVF) at 8 months. Secondary angiographic efficacy endpoints were binary restenosis at 8 months, in-stent minimum luminal diameter (MLD), and late loss. The safety endpoints included major adverse cardiac events as well as late aneurysm formation. The registry was designed to allow a statistically valid comparison of these results to the placebo group of the START 30 trial. Quantitative angiographic analysis was performed on the 8-month follow-up examination. Rates of restenosis were evaluated for various segments of the treated vessel. A separate analysis was performed to evaluate the relationship between vessel injury length and the radiated segment.

RESULTS

A total of 207 patients were entered into the START 40 registry. The postprocedure angiographic results, including the postprocedure MLD and percent diameter stenosis, were similar between the START 40 patients and the placebo group from the START trial in the stented segment of the treated vessel. Eight-month angiographic follow-up was available on 150 patients from the registry. The TLR rate was significantly reduced when compared to the placebo group (11% vs. 22.4% respectively, p = 0.008). A similar reduction was seen in terms of target vessel revascularization (15.9% vs. 24.1%, p = 0.03). The 8-month MLD was found to be significantly larger in the START 40 patients (1.85 mm vs. 1.47 mm, p < 0.0001). The difference seen in the clinical endpoint of TVF (19.3% vs. 25.9%) did not reach statistical significance (p = 0.1). Analysis of the procedural angiograms revealed mismatch between the length of vessel injured and the location of the 90% isodose in 46% of the treated cases. Angiographic analysis revealed that geographic miss was associated with a higher rate of binary restenosis (32% vs. 18% p = 0.04) in the analysis segment.

CONCLUSIONS

This multicenter registry demonstrates the safety and efficacy of a 40-mm 90Strontium/90Yttrium source train in the management of patients with in-stent restenosis. Restenosis rates were lowered with the use of this longer source train when compared to the placebo arm of the START trial for lesions with a maximum vessel injury length of 20 mm. Angiographic analysis identified the importance of the accurate delineation of injury length and correct source positioning. These results support the continued use of beta radiation for the treatment of this disease process.

Transradial coronary brachytherapy with the Novoste Beta-Rail system

We report our initial experience in 10 consecutive patients who underwent transradial coronary brachytherapy for in-stent restenosis using a 90Sr/Y source and the Novoste Beta-Rail system. In all patients, procedures were successfully completed using a right transradial approach. We performed the procedures with the Beta-Rail catheter using 7 Fr (Zuma II, Medtronic, MN; n = 5) or 8 Fr (Cordis, Miami, FL; n = 5) guiding catheters. All lesions were successfully dilated and no additional stent was inserted. We used a 40 mm source (n = 3) or a 60 mm source (n = 7) with manual stepping in four cases. In three cases, we did one stepping, and in one case, we did three steppings. The mean dwell time was 195 plus minus 44 sec. The mean delivered dose was 23 +/- 3 Gy at 2 mm distance from the source. No radiation treatment was interrupted. Mean fluoroscopy time was 26 +/- 13 min. Procedural success was achieved in all patients. Three patients had mild CK elevations (< 3 times upper normal limit). All patients were pretreated with clopidogrel (300 mg) and combined treatment with aspirin + clopidogrel is to be continued for at least 1 year. Clinical follow-up up to 3 months has not yielded any complication and all patients have remained free from angina.

Use of localised intracoronary beta radiation in treatment of in-stent restenosis: the INHIBIT randomised controlled trial

BACKGROUND

In-stent restenosis is a major limitation of intracoronary stenting. Ionising gamma radiation has been shown to reduce recurrence of restenosis after stent placement. We aimed to compare the effects of intracoronary beta radiation treatment with those of placebo for clinical and angiographic outcomes of patients with diffuse in-stent restenosis.

METHODS

332 patients with in-stent restenosis underwent successful coronary intervention, and were then randomly allocated to intracoronary beta radiation with a phosphorus-32 source (n=166) or placebo (166) delivered into a centreing balloon catheter through an automatic afterloader. Longer lesions (>22 mm of dilated length) were treated with tandem positioning of the study wire. The primary safety endpoint was major adverse cardiac events, defined as death, myocardial infarction, and repeat target-lesion revascularisation at 9 months. The primary efficacy endpoint was binary angiographic restenosis rate in the analysis segment during 9-months' follow-up. Analysis was by intention to treat.

FINDINGS

Procedural success, and in-hospital and 30-day complications were similar among the two groups. 24 (15%) patients in the radiated group had the primary safety endpoint of death, myocardial infarction, or repeat target-lesion revascularisation over 290 days compared with 51 [corrected] (31%) in the placebo group (difference 16% [95% CI 7-25], p = 0.0006). Binary angiographic restenosis rate was lower in the radiated group than the placebo group for the entire analysed segment (difference 25% [14--37], p < 0.0001).

INTERPRETATION

Vascular brachytherapy using pure beta-emitter 32P delivered into a centreing catheter via an automatic afterloader can be used to reduce overall revascularisation in patients undergoing treatment for diffuse in-stent restenosis.

Impact of geographic miss on adjacent coronary artery segments in diffuse in-stent restenosis with beta-radiation therapy: angiographic and intravascular ultrasound analysis

BACKGROUND

The impacts of geographic miss on edge restenosis have not been sufficiently evaluated.

METHODS

Beta-radiation therapy with rhenium 188-filled balloon after rotational atherectomy for diffuse in-stent restenosis was performed in 50 patients. We evaluated the impacts of geographic miss on adjacent coronary artery segments beyond the stent by angiographic (QCA) and intravascular ultrasound (IVUS) analysis in 50 irradiated lesions and 100 edges. Serial IVUS and QCA comparisons between postradiation and 6 months' follow-up were available in 44 and 47 of 50 patients, respectively. QCA measurements of minimal lumen diameter (MLD) and IVUS analysis were performed in the reference and radiation segments. Edges that were touched by the angioplasty balloon but were not adequately covered by radiation constituted the geographic miss edges.

RESULTS

Geographic miss was observed in 55.6% and 52.6% in QCA and IVUS analysis, respectively. Edge restenosis after radiation therapy in 3 patients was associated with geographic miss. In contrast to uninjured edges (postradiation 2.9 +/- 0.6 mm to follow-up 2.8 +/- 0.6 mm, P =.292), MLD in the radiation segment by QCA analysis significantly decreased from 2.7 +/- 0.4 mm to 2.4 +/- 0.6 mm in geographic miss edges (P =.002). IVUS analysis showed that significant positive remodeling in the radiation segment occurred in uninjured edges (vessel area from 15.4 +/- 4.4 mm2 to 15.8 +/- 4.4 mm2, P =.001) but not in geographic miss edges (vessel area from 12.8 +/- 3.6 mm2 to 13.0 +/- 3.6 mm2, P =.119).

CONCLUSION

The geographic miss might be one of the predictors, which resulted in decreased MLD at follow-up in beta-radiation therapy. Sufficient lesion coverage with radiation might be associated with positive remodeling in the radiation segment.

Repeated intracoronary beta radiation for recurrent in-stent restenosis

More than 70% of percutaneous coronary interventions are followed by a stent implantation. In-stent restenosis still occurs in 20-30% of patients and remains a therapeutic challenge. At present only vascular brachytherapy has been shown to be an effective treatment option. We report here one case of recurrent in-stent restenosis after vascular brachytherapy that was successfully treated by a second beta radiation treatment.

Centered versus noncentered source for intracoronary artery radiation therapy: a model based on the Scripps Trial

BACKGROUND

The Scripps Trial was a randomized study of intracoronary artery radiation therapy with iridium 192 used to treat restenotic vessels. We used the intravascular ultrasound data from the Scripps Trial to investigate whether a lumen-centered gamma or beta radiation source would reduce radiation dose heterogeneity compared with the noncentered source position used.

METHODS

Analysis included 28 patients with stent placement in 20 native vessels and 8 saphenous vein grafts enrolled in this trial. Radiation dosimetry for gamma radiation was calculated to deliver 800 cGy to the far field target, provided the maximum dose to the near field target did not exceed 3000 cGy. Prescribed dosimetry for beta radiation by use of yttrium 90 was 1600 cGy at 2 mm distance from the source.

RESULTS

The calculated average minimum source to target distance by use of a lumen-centered source increased by 0.18 mm from 1.70 +/- 0.25 to 1.88 +/- 0.36 mm, whereas the maximum distance decreased by 0.17 mm from 3.64 +/- 0.60 to 3.47 +/- 0.43 mm (P <.05). On the basis of these distances, the maximum radiation dose, as well as radiation dose heterogeneity (ratio of maximum to minimum), would have been reduced in 22 of 28 patients by use of a lumen-centered gamma or beta source (P <.005). The reduction in dose heterogeneity was substantially greater with a beta source compared with a gamma source (48% vs 16% reduction).

CONCLUSIONS

Centering of the intracoronary artery radiation therapy delivery catheter within the vessel lumen can significantly reduce radiation dose heterogeneity when compared with a noncentered source position. This dose reduction is substantially greater for a beta compared with a gamma source.

Coronary in-stent restenosis: current status and future strategies

In-stent restenosis (ISR) is a novel pathobiologic process, histologically distinct from restenosis after balloon angioplasty and comprised largely of neointima formation. As percutaneous coronary intervention increasingly involves the use of stents, ISR is also becoming correspondingly more frequent. In this review, we examine the available studies of the histology and pathogenesis of ISR, with particular reference to porcine and other animal models. An overview of mechanical treatments is then provided, which includes PTCA, directional coronary atherectomy and high speed rotational atherectomy. Radiation-based therapies are discussed, including a summary of current problems associated with this modality of treatment. Finally, novel strategies for the prevention of ISR are addressed, including novel developments in stents and stent coatings, conventional drugs, nucleic acid-based drugs and gene transfer. Until recently, limited pharmacologic and mechanical treatment options have been available for both treatment and prevention of ISR. However, recent advances in gene modification and gene transfer therapies and, more particularly, in local stent-based drug delivery systems make it conceivable that the incidence of ISR will now be seriously challenged.

Targeting the adventitia with intracoronary beta-radiation: comparison of two dose prescriptions and the role of centering coronary arteries

PURPOSE

To compare by intravascular ultrasound (IVUS) the efficacy of delivering the prescribed dose to the adventitia between two commonly used dose prescriptions for intracoronary radiotherapy.

METHODS AND MATERIALS

In 59 human postangioplasty coronary vessels, one IVUS cross-section (1 mm thick) with the highest plaque burden was used for creating dose-volume histograms with different hypothetical positions of the source.

RESULTS

On average, prescription to 1 mm beyond lumen surface resulted in delivery of the prescribed dose (20 Gy +/- 20%) to a higher fraction of adventitial volume than with the prescription to 2 mm from the source, with source placed in vessel center, lumen center, or in the IVUS catheter position. Source placement in the lumen center resulted in a low dose heterogeneity to the adventitia and the least dose heterogeneity to the intima.

CONCLUSIONS

Prescription to 1 mm beyond lumen surface appeared more effective in delivering the prescribed dose to the adventitia than the American Association of Physicists in Medicine (AAPM) recommended prescription to 2 mm from the source center. Moreover, centering the source in the lumen provides the better balance of effective adventitial targeting and intimal dose homogeneity. Modification of the current AAPM recommendation for dose prescription for intracoronary radiotherapy should be considered.

Nuclear Regulatory Commission regulatory status of approved intravascular brachytherapy systems

PURPOSE

To review current and potential future regulatory status of intravascular brachytherapy (IVB) systems.

METHODS

There are three approved IVB systems; two commercial IVBs are hand-operated manual devices; the third is remotely operated. In three Guidances, the Nuclear Regulatory Commission (NRC) applied certain regulatory concepts applicable to remotely operated high dose rate (HDR) afterloaders to manually operated IVBs. This article reviews these Guidances, newly released NRC regulations on the medical use of by-product material, and potential regulatory issues related to IVB systems.

RESULTS

The Guidances are specific. However, newly released NRC regulations on the medical use of byproduct material, including HDR afterloaders, omit IVB systems as a category. NRC licensure of IVB systems is considered case-by-case.

CONCLUSIONS

The current limited application of regulations applicable to HDR remote afterloaders to hand-held IVB systems could lead to other HDR-like regulations for hand-held IVB systems in future regulations.

Required treatment margin for coronary endovascular brachytherapy with iridium-192 seed ribbon

PURPOSE

Preliminary clinical trials (SCRIPPS I, WRIST and Gamma 1) employing catheter-based endovascular brachytherapy (EVBT) with iridium-192 (Ir-192) seeds show promising results in reducing restenosis after coronary intervention. Failure analysis of these studies showed a significant number of restenosis at the treatment margin called "edge effect." The objective of this study is to investigate the factors that contribute to the adequacy of treatment margin.

METHODS AND MATERIALS

The factors contributing to the margins are penumbra effect at the end of the seed train, uncertainty in target localization, longitudinal seed movement during cardiac cycle and barotrauma due to stent deployment. The magnitudes of the penumbra effect, which refers to the tapering off the prescribed isodose line near the ends of the source train, were calculated for various source lengths of Ir-192 seed ribbon using AAPM TG-43 algorithm. Uncertainty in target localization refers to the fact that the visual estimation of proximal and distal extent of the injury is not accurate, and this can be obtained by comparing the "estimate" from the interventional cardiologist with careful review of the cine-angiogram. Longitudinal seed movements relative to the coronary vessel during the cardiac cycle were determined by frame-by-frame reviewing cine-angiograms of 30 patients. The proximal and distal source points were measured in reference to branching vessels during the contrast phase of the cine-angiogram. The maximum proximal and distal longitudinal movement was captured and source displacement was measured from the closest proximal and distal branching vessel. Barotrauma, additional injury to the vessel arising from the stent deployment balloon, was obtained by reviewing specifications from commercially available stent delivery systems.

RESULTS

The penumbra effect ranges from 3.9 to 4.5 mm for 6-22 Ir-192 seed ribbons. The uncertainty in target localization is within 3 mm for our interventional cardiologists. The results of seed movements were categorized by three major coronary vessels and by proximal versus distal ends. The mean and standard deviation of seed movement are 1.1 and 0.8 mm, respectively. The average length of barotrauma beyond the stent margins for reviewed stents was 1.7 mm, ranging from 0.5 to 2.5 mm.

CONCLUSION

A minimum of 8-mm treatment margin is recommended for coronary vascular brachytherapy with Ir-192 seed ribbon. This was derived by considering the above contributing factors. Excessive margins should be avoided due to possible increase risk of late effect. By providing adequate treatment margins, one can avoid geographic miss; hence, one can further improve the effect of EVBT in reducing restenosis.

Safety and efficacy of manual stepping and overlapping of beta-emitter for diffuse in-stent restenosis lesions

BACKGROUND

The effects of overlapping beta-emitter sources on the treatment of in-stent restenosis (ISR) lesions as a result of manual stepping are unknown.

METHODS AND RESULTS

In the BETA WRIST (Beta Washington Radiation for In-stent Restenosis Trial), 17 out of the 50 patients who received radiation treatment had diffuse ISR in native coronaries that required manual stepping of the beta-emitter (90Y) source in order to cover the lesion and the edges. Fourteen of those patients received radiation with an overlap of up to 3 mm in the middle of the stented segment. The prescribed dose was 20.6 Gy to a distance of 1.0 mm from the surface of the inflated balloon, and the calculated dose to the vessel wall at the overlapped area did not exceed 75 Gy. There was no difference in late total occlusion (7.1% vs. 9.0%, P=NS) and target lesion revascularization (28.5% vs. 27.2%, P=NS) between patients with stepping and those without stepping. At 6 months, there was no evidence of perforation or aneurysm at the overlapped segments. Quantitative coronary angiographic (QCA) analysis revealed significantly reduced late loss in the overlapped segment compared to the adjacent segment (P=.04). Serial (postradiation vs. follow-up) IVUS measurement showed larger mean lumen cross-sectional area (CSA) (P=.0035) and smaller mean intimal hyperplasia (IH) CSA (P=.0010) in the overlapped segment compared to the adjacent segment.

CONCLUSION

Manual stepping of beta-emitter source with a short overlapped segment is safe for diffuse ISR. Further increase in lumen dimension and reduction in IH formation are observed at the overlapped segment.

Prevention of restenosis after percutaneous coronary intervention: the continuing challenge

Percutaneous coronary intervention with angioplasty and stenting is well established in the treatment of coronary artery disease. However, the many advances in technique and equipment over the last couple of decades have yet to significantly reduce the incidence of restenosis. This Achilles' heel has necessitated frequent re-interventions and also introduced a new iatrogenic disease of in-stent restenosis. Brachytherapy and coated stents may be the answer to this difficult problem. Many papers have been published in the last few years on these two new modalities of treatment, and we review the evidence available so far. Early results show that brachytherapy significantly reduce the incidence of restenosis when used in restenotic lesions, and coated stents significantly reduce restenosis in de novo lesions. This early promise of brachytherapy and coated stents, if confirmed in longer-term studies, will represent a breakthrough in the battle against restenosis and may dramatically change the practice of interventional cardiology in the near future.

Intracoronary beta radiation: state of the art

This state-of-the-art review is intended to explore the development of beta radiation including catheter delivered and permanent implants from its inception to current practice. Specific focus will be given to the isotopes currently available, radiation physics of beta emitters, preclinical studies, clinical trials, beta radiation delivery systems, and implications for future practice. The encouraging results from the clinical trials have established vascular brachytherapy as a standard of care for patients with in-stent restenosis. Vascular brachytherapy requires additional "fine-tuning" to achieve full optimization.