Intracoronary radiation decreases the second phase of intimal hyperplasia in a repeat balloon angioplasty model of restenosis

Prevention of coronary restenosis with radiation therapy: a review

The problem of restenosis after percutaneous transluminal coronary angioplasty remains the major limiting factor of the procedure. Over the last 10 years, investigators have been studying the use of radiation therapy for preventing restenosis after angioplasty or stent placement. Since radiotherapy has been proven in other cases to be effective in disrupting the cell cycle regulatory proteins and thereby slowing or stopping growth, it was decided to apply the same principle to neointimal hyperplasia. To review the data that have emerged regarding vascular radiation with an emphasis on irradiated stents, 65 articles were reviewed and both preclinical and clinical experiments were included. Overall, studies with gamma and beta radiation show promising results. Endovascular gamma radiation has been shown effective in randomized trials, even at 3-year follow-up. Beta radiation is preferred because of greater safety and localization, and because it has also shown encouraging results in initial clinical trials, as well as in larger randomized studies. Consequently, the Federal Drug Administration has approved the use of both. In both types of endovascular brachytherapy, it seems the greater the dose, the better the initial response. Safety concerns include an increased incidence of late thrombosis and greater restenosis at margins. With irradiated stents, however, the situation is not as clear. At times, animal models have presented confusing results. These have ranged from significant suppression of hyperplasia to outright adverse effects of radiation on the vessel wall. While some clinical trials have been encouraging, others have not. Follow-up of up to 1 year has been disappointing so far. Many issues, such as the "candy wrapper" effect and rebound hyperplasia, must be dealt with before this becomes a viable form of therapy. It has become clear that radiation therapy in this setting, while having potentially great benefits, can cause deleterious effects as well. However, the mixed bag of positive and negative results seen so far, and the attractiveness of stents or percutaneous transluminal coronary angioplasty being "restenosis-proofed," eventually is cause for cautious optimism.

Dose mapping of porcine coronary arteries using an optical fiber dosimeter

BACKGROUND

This study is about the measurement of radiation dose contribution to the coronary arteries during intravascular brachytherapy with beta and gamma emitters utilizing in vivo optical fiber dosimeters.

METHODS AND MATERIALS

Domestic pigs were used. With each measurement, catheters were introduced into two different coronary arteries, including the left circumflex (LCX), the left anterior descending (LAD), the first diagonal, and/or the right coronary artery (RCA). A radioactive source (192Ir, 90Sr/Y, or 32P) and the dosimeter were loaded in each of these catheters. Data were collected as the dosimeter was being retracted at a constant rate via computer control.

RESULTS

The radiation dose was normalized to 100% at a 2-mm radial distance from the source. When radiating a branching artery, the dose to the bifurcation at 5 mm from the source was 35%, 10%, and 3% for the 192Ir (10 seeds), 90Sr/Y (40 mm), and 32P sources, respectively. When utilizing a 23-seed 192Ir source, the dose is 40% at a 5-mm distance. However, radiation of the RCA did not result in dosing to the LAD or LCX using any source.

CONCLUSIONS

The dose to adjacent artery segments is less with beta than with gamma emitters. Significant dose exposition is noted when using gamma emitters at a distance of 5 mm. The results can serve as a guideline for establishing prescription doses and safety margins for the treatment of bifurcation lesions and retreatment of the arteries.

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.

Endovascular brachytherapy after percutaneous transluminal angioplasty of recurrent femoropopliteal obstructions

PURPOSE

To test the preventive effect of endovascular brachytherapy (EVBT) on restenosis following secondary angioplasty in patients with presumed neointimal restenosis in the femoropopliteal segment.

METHODS

From March 1997 through May 2000, 100 patients (58 men; mean age 70 years, range 45-87) with postangioplasty femoropopliteal segment restenoses were enrolled and randomized to treatment with repeat angioplasty and EVBT (n=51) or to angioplasty alone (n=49) as control. The groups were similar with regard to demographics and lesion characteristics. High-dose-rate EVBT was performed with (192)Ir irradiation without a centering device (12 Gy for a reference vessel radius of 3 mm and a 2-mm reference depth). Primary endpoint in the 1-year follow-up was recurrent obstruction >50% documented by duplex ultrasound; the secondary endpoint was clinical improvement.

RESULTS

Only 44 (86%) of 51 patients received adequate EVBT due to technical failure, so the 7 failures were included with the controls in the per-protocol adherence analysis. At 1 year, the patients receiving EVBT had a restenosis rate of 23% (10/44), which differed significantly (p<0.028) from the 42% (23/56) rate in controls. Clinical results tended to be better with EVBT, but differences did not achieve statistical significance.

CONCLUSIONS

EVBT without a centering device reduced restenosis significantly in patients with recurrent stenosis after angioplasty, which confirms previous results in primary long-segment femoropopliteal obstructions.

Effects of brachytherapy on intimal hyperplasia in arteriovenous fistulas in a porcine model

PURPOSE

The hypotheses of this investigation were that endovascular radiation would reduce intimal hyperplasia in arteriovenous fistulas (AVFs) and that this reduction would be associated with decreased expression of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF)-A, and tumor necrosis factor (TNF)-alpha.

MATERIALS AND METHODS

Bilateral end jugular vein-to-side carotid artery fistulas were constructed in pigs. At 48 hours, one AVF was randomly selected for endovascular radiation with (192) Iridium. The contralateral fistula received no radiation and served as a control. Animals in group 1 (n = 7) received 14 Gy of radiation at a depth of 2 mm and tissue was harvested at 29 days; animals in group 2 received 7 Gy of radiation at a depth of 2 mm and tissue was harvested at 29 days (n = 8); and animals in group 3 received 7 Gy of radiation at a depth of 2 mm and tissue was harvested at 56 days (n = 8). The area and maximum thickness of intimal hyperplasia were then measured blindly. Immunohistochemical results for VEGF, PDGF-A, and TNFalpha were obtained and analyzed blindly by assigning a score of 0-3, with 0 indicating no staining and 3 indicating maximum staining.

RESULTS

Irradiation with 14 Gy caused severe fibrosis in the media of the vein, with thrombosis of three of seven AVFs. Compared with the control group, the group that underwent irradiation with 7 Gy had significantly reduced intimal area at 56 days (9.9 mm(2) +/- 4.9 vs 2.1 mm(2) +/- 1.1; P =.001). This reduction correlated with significant reduction in the expression of VEGF (score of 2.2 +/- 0.1 vs 1.2 +/- 0.2; P =.001) and TNFalpha (1.3 +/- 0.1 vs 0.9 +/- 0.1; P =.04).

CONCLUSION

Fourteen grays is an excessive radiation dose for veins, causing medial fibrosis and thrombosis of the AVF. Irradiation with 7 Gy effectively inhibited the formation of intimal hyperplasia in AVF. This inhibition correlated with decreased expression of VEGF and TNFalpha.

Effectiveness of radioactive tungsten source in the prevention of restenosis in stented porcine coronary arteries

PURPOSE

Intracoronary radiation has shown the potential to inhibit neointimal proliferation in porcine models of restenosis. The objective of this study was to determine whether intracoronary radiation using a new coiled wire of tungsten-188 ((188)W), a pure beta emitter (half-life 69.4 days) is safe. In addition, a dose of 0 Gy, 18 Gy, or 25 Gy prescribed to 2 mm from the center of the source and delivered intraluminally is sufficient to prevent restenosis and free from adverse effects.

METHODS AND MATERIALS

Ten domestic swine underwent 13-mm stent implantation (SI) into two arteries, left anterior descending plus either the left circumflex or right coronary artery. After SI, a closed-end lumen radiation catheter was inserted to the treated artery and a 40-mm coiled (188)W source was manually delivered to cover the stented segment and its margins. A total of 20 arteries were randomized to treatment with a radiation dose of 0, 18 Gy, or 25 Gy delivered to 2 mm depth from the center of the source. Four weeks after the procedure, the swine underwent angiography and intravascular ultrasound using automated pullback at 0.5 mm/s. before being killed and the arteries perfusion fixed. Histopathologic and histomorphometric analyses were performed at 28 days after injury and radiation.

RESULTS

Irradiation with (188)W at a dose of 25 Gy after SI significantly inhibited neointima formation (intimal area: 1.05 +/- 0.64 vs. 2.75 +/- 0.99 mm(2), p < 0.01) and at an 18 Gy dose of radiation (intimal area: 1.73 +/- 0.49 vs. 2.75 +/- 0.99 mm(2)), as compared to controls. One artery receiving 18 Gy and two arteries receiving 25 Gy were totally occluded at follow-up due to thrombus formation but no edge stenosis was observed in any of the irradiated arteries.

CONCLUSIONS

Intracoronary radiation therapy using a new coiled wire of (188)W source delivered after SI appeared to be safe and well tolerated. The radiation doses demonstrated efficacy in reducing neointima formation in the porcine coronary stent injury model.

Histomorphometric evaluation of (198)Au endovascular brachytherapy in a renal artery restenosis model in rabbits

OBJECTIVE

The main mid-term complication of percutaneous transluminal angioplasty of the renal artery is restenosis, which occurs in up to 50% of patients. Although no pharmacologic agent to date has been effective in preventing restenosis, both beta-ray emitters and gamma-ray emitters used in endovascular brachytherapy have been shown to reduce coronary restenosis. The objectives of this study were to evaluate the efficacy of (198)Au endovascular brachytherapy in preventing restenosis after percutaneous transluminal renal angioplasty and to determine the radiation dose to the operator.

MATERIALS AND METHODS

Twenty-one New Zealand white rabbits (10 females and 11 males) weighing an average of 3.5 kg (range, 3.2-3.8 kg) who had been fed a normal diet underwent bilateral 33% overdilatation with deendothelialization of the renal arteries. After 7 weeks, the induced renal artery stenoses were treated by percutaneous transluminal renal angioplasty. The rabbits were randomly assigned to one of three groups before receiving endovascular 25-Gy irradiation at a radial 2.0-mm depth with a 0.5 x 15 mm (198)Au wire (106 MBq). The right renal artery was irradiated in group A; the left, in group B. The rabbits in group C randomly received a right- or left-sided dummy wire. Operator exposure to radiation was measured using thermoluminescent dosimeters and ionization chambers. The rabbits were sacrificed after 3 weeks. The aorta and renal arteries were perfusion-fixed. The renal arteries were removed for histologic and histomorphometric study.

RESULTS

Forty-two renal arteries were cut into a series of 4- micro m-thick slices. Five arteries were thrombosed (two in the irradiated group and three in the control group, p > 0.05). In the patent arteries (n = 37), the average neointimal area was 0.068 mm(2) (range, 0.009-0.234 mm(2)) in 15 irradiated segments (315 slices total), whereas the average neointimal area was 0.135 mm(2) (range, 0.016-0.324 mm(2)) in 22 control segments (462 slices total) (analysis of variance, p < 0.009), showing a percentage area of restenosis of 10.4% in irradiated arteries and 43.4% in non-irradiated arteries (p < 0.0003). Radiation dose per procedure to the operator was 0.034 mSv in the index finger, 0.024 mSv in the wrist, and undectable in the body.

CONCLUSION

Endovascular brachytherapy with (198)Au appears to inhibit early renal artery restenosis and exposes the operator to a safe level of radiation.

Coronary artery brachytherapy

Coronary artery disease is the leading cause of mortality in the West with over 1.2 million angioplasties performed annually. Despite the introduction of stents, restenosis occurs in 30-40% of vessels, which until recently has only been treated effectively by coronary artery bypass surgery. Coronary artery brachytherapy appears to provide an alternative, less invasive remedy. The mechanisms of restenosis and how these are inhibited by radiation are described here. The practicalities of radiation delivery and the history of the development of intravascular radiation as an effective clinical tool are outlined. Finally, the pitfalls of the current technology and the areas in which future research must be targeted for the field to develop are discussed.

Dose volume histogram assessment of late stent malapposition after intravascular brachytherapy

PURPOSE

Positive remodeling and decreased neointima proliferation are among the causes for Late Stent Malapposition (LSM). It was our interest to investigate a possible relationship between dose and incidence of LSM.

METHODS

Index and follow up IVUS examinations of 238 patients (152 treated with Intravascular Brachytherapy (IVBT), 86 control) enrolled in IVBT trials were reviewed to identify patients with LSM. 7.2% of patients treated with IVBT and 2.3% of patients in the control group were found to have LSM on their 6-month follow-up IVUS. Using the index IVUS study. Dose Volume Histograms (DVH) were constructed for a segment of the adventitia comprising an arc deep to the area where LSM is present at follow up. For control, two areas: an arc deep to complete apposition (Control 1) and a segment within the stent but 5 mm apart from the LSM (Control 2). Volumes were defined by IVUS images that were 1 mm apart and the media-adventitial contour was taken to be 0.5 mm thick from the border.

RESULTS

DVH of 90% and 50% adventitial volume of LSM area received a significantly (p < .05) higher dose compared to both controls. Calculated are 12 LSM sites in 9 patients and 9 control sites. At all 12 sites Mean Cross Sectional Area of External Elastic Membrane (EEM CSA) was significantly larger in the LSM group at follow up compared to index (p-.001).

CONCLUSIONS

DVH analysis showed a positive correlation between radiation dose to the adventitia and incidence of LSM. The myofibroblasts in the adventitia are known to be the target for irradiation. Proliferation of myofibroblasts leads to neointima formation. LSM may be due to the higher dosages delivered to 50% and 90% of the adventitia volume (LSM area) which may have led to profound neointima suppression. In turn the neointima could not compensate positive remodeling reflected by an increase in EEM CSA.

Inaccuracy in manual multisegmental irradiation in coronary arteries

PURPOSE

Retrospective evaluation of the accuracy of manual multisegmental irradiation with a source train for irradiation of long (re)stenotic lesions in coronary arteries, following percutaneous transluminal coronary angioplasty (PTCA).

MATERIAL AND METHODS

Thirty-six patients were treated with intracoronary irradiation following PTCA with manual multisegmental irradiation. These patients were included in the multicenter, multinational 'European Surveillance Registry with the Novoste Beta-Cath system' (RENO). In all 36 patients the target length (i.e. PTCA length plus 5-mm margin at each side) was too long for the available source train lengths (30 and 40 mm). In 33 patients the radiation delivery catheter was manually positioned twice and in three patients three times in series, trying to avoid any gap or overlap. The total number of junctions was 39. Following a successful PTCA procedure the site of angioplasty was irradiated using the Novoste Beta-Cath afterloader with a 5-F non-centered catheter which accommodates the sealed beta-emitting (90)Sr/(90)Y source train or dummy source train. Radiation was delivered first to the distal part of the target length. Fluoroscopic images of this source position were stored in the computer memory. For irradiation of the proximal part of the target length, the delivery catheter had to be retracted over a distance equal to the source length used for the distal part. This was done by a continuous overlay video loop with ECG-gated replay of the image stored in the computer memory. The dummy source was used to position the delivery catheter so that the junction between both source positions was as precise as possible. Measurements of gap or overlap between the source positions were performed retrospectively on printed images. Doses were calculated, in accordance with the Novoste study protocol, at a distance of 2 mm from the source axis (=dose prescription distance) in several points along the irradiated length.

RESULTS

Interventional or PTCA length varied between 33 and 95 mm. The lesion sites were in the left anterior descending artery, (n=6), right coronary artery (n=20), left circumflex artery (n=6) and one vein graft. The administered radiation dose was determined by the vessel diameter and the presence of a stent. This dose, prescribed at a distance of 2 mm from the source axis, varied between 16 and 22 Gy. No gap or overlap was seen between the two source trains in only two out of 39 cases. In 16 cases there was a gap ranging between 0.6 and 9.6 mm and 18 cases showed an overlap of 0.5-14.4 mm. In three patients the measurement was not possible. In case of a gap the minimal dose calculated at 2 mm from the source axis varies between 0 and 87% of the prescribed dose, depending on the distance between both sources. In case of overlap the maximal dose varies between 110 and 200% of the prescribed dose at 2 mm from the source axis.

CONCLUSIONS

The results show the inaccuracy of manual multisegmental irradiation using a source train in coronary arteries, causing unacceptable dose inhomogeneities at a distance of 2 mm from the source axis at the junction between both source positions. Moreover, a perfect junction will never be possible due to movement of the non-centered radiation delivery catheter in the vessel lumen, as applied in this study. Manual multisegmental irradiation is therefore not recommended. Using longer line sources or source trains or preferably an automated stepping source is a more reliable and safer technique for treatment of long lesions.

Rationale for coronary artery radiation therapy

Within the past decade, focus on radiation to prevent restenosis has moved from a concept developed in the animal laboratory to a clinical treatment. The initial evaluation of coronary artery radiation therapy focused on changes in the function of the artery or lesion formation following overstretch balloon injury in pigs. A number of concepts emerged from this work: (1) radiation inhibits neointima formation in a dose-dependent fashion, (2) radiation prevents negative remodeling, (3) radiation does not reverse established injury, (4) low dose irradiation in an injured area may be injurious, (5) radiation is a useful adjunct to stenting, (6) benefits of radiation in animal models at 6 months are less pronounced than at 1 month, (7) radiation delays healing, (8) permanent stents and radiation delivered from external sources may have very different effects on restenosis, and (9) radiation interferes with vessel wall function. More recent studies of irradiation have looked at the molecular biological effects of radiation in hopes of understanding how this therapy works, and how it may be improved. This article attempts to summarize the known animal and cellular work on radiation in preventing restenosis.

Evaluation of renal arteries with use of gadoterate meglumine-, CO(2)-, and iodixanol-enhanced DSA measurements versus histomorphometry in renal artery restenosis in rabbits

PURPOSE

To experimentally evaluate gadolinium (Gd)-, carbon dioxide (CO(2))-, and iodixanol-enhanced digital subtraction angiography (DSA) versus histomorphometry in the assessment of renal artery stenosis.

MATERIALS AND METHODS

Fifteen male New Zealand White rabbits weighing 4.0 kg underwent percutaneous catheterization. Renal artery stenosis was induced by bilateral overdilation-deendothelialization (balloon diameter = 2 mm). The percentage of artery overdilation was 33%. After 4 weeks, the rabbits were randomized into two groups: group A underwent right-sided therapeutic percutaneous transluminal renal angioplasty (PTRA) (balloon diameter = 1.5 mm). After another 4 weeks, the renal arteries were evaluated by gadoterate-, iodixanol-, and CO(2)-enhanced selective quantitative DSA. The rabbits were then killed and renal arteries were perfusion-fixed for 60 minutes. Serial orcein-stained 4-um-thick slices were prepared for histomorphometry.

RESULTS

Based on morphometric data of single-stenosis versus post-PTRA restenosis lesions, no significant difference was observed between Gd- and iodixanol-enhanced quantitative DSA (r(2) > 0.95), although the iodine/Gd density ratio was equal to 3.5. Carbon dioxide less reliably allowed quantitative DSA (r(2) < 0.75).

CONCLUSION

Gd-based contrast agents represent a highly reliable alternative in experimental quantitative DSA evaluation of renal artery restenosis.

Dosimetry characterization of 32P catheter-based vascular brachytherapy source wire

Dosimetry measurements and Monte Carlo simulations for a catheter-based 32P endovascular brachytherapy source wire are described. The measured dose rates were obtained using both radiochromic dye film and an automated plastic scintillator. The investigated source has dimensions of 27 mm in length and 0.24 mm in diameter, and is encapsulated in NiTi. For the radiochromic film measurements, calibrated radiochromic dye film was irradiated at distances between 1 and 5 mm from the source axis in A-150 plastic, and read out with a high-resolution scanning densitometer. The depth-dose curve measured in A-150 is then converted to that in water using correction factors obtained from Monte Carlo calculations. For the scintillator system, direct measurements in water were acquired at distances between 1 and 6 mm from the center of the source, along the perpendicular bisector of the source axis. The scintillator was calibrated in terms of absorbed-dose rate in a reference beta-particle field at multiple depths. The measured dose rates obtained from the film and scintillator measurements were then normalized to the measured source activity, i.e., to convert the measured data to units of cGy/s/mCi. Theoretical dosimetry calculations of the catheter-based 32P wire geometry were also obtained from Monte Carlo simulations using the Electron Gamma Shower code (EGS4), the Monte Carlo N-particle transport code (MCNP4B), and CYLTRAN from the Integrated Tiger Series codes (ITS v.3) and found to be in good agreement. The results of both measurements and calculations are expressed as absorbed-dose rate in water per unit of contained activity (cGy/s/mCi). Comparisons indicate that the measured and calculated dosimetry are in good agreement (<10%) within the relevant treatment distances (1-5 mm). This work fully characterizes the radiation field around a novel 32P beta brachytherapy source in water. The depth-dose curve can be used to calculate the dose to the vessel wall from a 27 mm 32P source wire centered within the vessel lumen.

Long-term adverse effects of radiation inhibition of restenosis: radiation injury to the aorta and branch arteries in a canine model

PURPOSE

To determine the long-term effects of irradiation on large arteries in view of the possible use of radiation to prevent restenosis after angioplasty.

METHODS AND MATERIALS

Groups of dogs received 10-55 Gy single-dose alone, or in combination with 50 Gy in 2-Gy fractions, or 50-80 Gy in 2-2.7-Gy fractions to an 8-cm length of aorta and branch arteries. Single doses were delivered intraoperatively. Two or 5 years after irradiation, aortas and branch arteries were evaluated histomorphometrically to determine areas of intima, media, and adventitia, and qualitatively to determine other adverse effects.

RESULTS

Intimal area increased at single doses < 20 Gy and after all fractionated doses, but was normal at doses > 20 Gy 2 years after irradiation. Intimal area was greater at 5 years than at 2 years after irradiation. Adventitial area increased with increasing dose at 2 and 5 years after irradiation. Thrombosis of the aorta and branch arteries occurred at 4-5 years after irradiation with ED50s of 29.7 Gy and about 25 Gy, respectively, but did not occur after fractionated irradiation.

CONCLUSION

Intimal proliferation is inhibited at single doses > 20 Gy, but may be stimulated at single doses of < 20 Gy or after fractionated irradiation. Adventitial fibrosis increases with increasing dose and could contribute to adverse late vascular remodeling. Severe adverse effects were not evident until 4-5 years after irradiation at does of > 20 Gy to an 8-cm vessel length.

Radiation therapy to prevent coronary artery restenosis

The problem of restenosis after coronary angioplasty remains a major limiting factor of the procedure. Intracoronary stenting has led to a modest reduction in the frequency of this event. In the early 1990s, the effectiveness of ionizing radiation combined with balloon angioplasty and stenting was first convincingly demonstrated in animal models of restenosis. Small feasibility studies and two randomized trials have, in general, supported the promise of these initial preclinical studies in the prevention of restenosis. Much remains to be learned about the application of radiation for this therapy. This article reviews the current status of preclinical and clinical investigation of this therapy.

[Role of intravascular brachytherapy in the prevention of vascular restenosis after angioplasty]

About 30% of patients who underwent percutaneous transluminal coronary angioplasty show evidence of restenosis, which appears to be independent of the angioplasty method used. The restenosis is due of two factors, firstly migration of smooth vascular muscle cells of the vascular media to the intima and multiplication which lead to the formation of a neo-intima. Irradiation limits the proliferation by acting of the cells in the mitotic stage. The vascular target volume is not very thick and is difficult to define it, that why brachytherapy seems to be the best procedure to prevent restenosis. However, the development of this treatment present many difficulties. Different irradiation techniques have been studied. Such techniques include catheter containing radioactive sealed source, radioactive stent, or balloon containing radioactive liquid inside. Each of these methods have their own advantages, inconveniences, problems and risks. Radioisotope may be either beta or gamma emitters. Gamma emitter presents problems for radioprotection but the satisfactory dose distribution may be difficult to obtain using beta emitter. Choice of dose, dose rate and delay between the end of angioplasty and the beginning of brachytherapy is subject to some discuss. Animal experiments using radioisotope have shown reduction in cell proliferation. Human trials showed feasibility, safety of the method and real impact on restenosis prevention. However, long-term efficacy has not been proved because the follow-up of the patients is too short. A randomized trial of 192Ir brachytherapy for prevention of restenosis has recently shown the efficacy in short and median term. However, long term efficiency and secondary effects have not yet been established as the follow up time of this study is still too short. That is why, collaboration between cardiologists and radiotherapists and physicists is indispensable to enable the development of an optimal technique.