(Circulation. 2000;101:2472.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
Residual Plaque Burden, Delivered Dose, and Tissue Composition Predict 6-Month Outcome After Balloon Angioplasty and ß-Radiation Therapy
From the Thoraxcenter, Heartcenter, Rotterdam, Dijkzigt Academisch Ziekenhuis Rotterdam, The Netherlands (M.S., S.G.C., I.P.K., W.J.v.d.G., J.M.R.L., E.B., M.A.C., P.W.S.), and Daniel den Hoed Cancer Center, Rotterdam, The Netherlands (J.P.A.M., V.L.M.A.C., P.C.L.).
Correspondence to Prof P.W. Serruys, MD, PhD, Heartcenter, Academisch Ziekenhuis Rotterdam, Erasmus University, Bd 418, PO Box 2040, Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands. E-mail serruys{at}card.azr.nl
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Abstract |
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Background—Inhomogeneity of dose distribution and anatomic aspects of the atherosclerotic plaque may influence the outcome of irradiated lesions after balloon angioplasty (BA). We evaluated the influence of delivered dose and morphological characteristics of coronary stenoses treated with ß-radiation after BA.
Methods and Results—Eighteen consecutive patients treated according to the Beta Energy Restenosis Trial 1.5 were included in the study. The site of angioplasty was irradiated with the use of a ß-emitting 90Sr/90Y source. With the side branches used as anatomic landmarks, the irradiated area was identified and volumetric assessment was performed by 3D intracoronary ultrasound imaging after treatment and at 6 months. The type of tissue, the presence of dissection, and the vessel volumes were assessed every 2 mm within the irradiated area. The minimal dose absorbed by 90% of the adventitial volume (Dv90Adv) was calculated in each 2-mm segment. Diffuse calcified subsegments and those containing side branches were excluded. Two hundred six coronary subsegments were studied. Of those, 55 were defined as soft, 129 as hard, and 22 as normal/intimal thickening. Plaque volume showed less increase in hard segments as compared with soft and normal/intimal thickening segments (P<0.0001). Dv90Adv was associated with plaque volume at follow-up after a polynomial equation with linear and nonlinear components (r=0.71; P=0.0001). The multivariate regression analysis identified the independent predictors of the plaque volume at follow-up: plaque volume after treatment, Dv90Adv, and type of plaque.
Conclusions—Residual plaque burden, delivered dose, and tissue composition play a fundamental role in the volumetric outcome at 6-month follow-up after ß-radiation therapy and BA.
Key Words: balloon • angioplasty • radioisotopes • ultrasonics • restenosis
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Endovascular radiation therapy is a promising new technique aimed at preventing restenosis after percutaneous coronary intervention.1 2 3 Although its effectiveness has been proven in the treatment of in-stent restenosis,4 the value of intracoronary irradiation in de novo coronary lesions remains to be established. Radiation delivered to the coronary artery by means of catheter-based systems can use both
- and ß-emitters.5 Long-term results after
treatment may be influenced by absolute dose and by the homogeneity in
dose distribution. ß-Emitters demonstrate a more rapid dose fall-off
than -emitters because of the short range of
electrons.6 This feature may lead to a less
homogeneous dose distribution when treating
coronary segments with variable degrees of curvature,
tapering, remodeling, and plaque extent. The use of dose-volume
histograms allows one to evaluate the cumulative dose received by a
certain specified tissue volume7 and has been recently
implemented in the field of intracoronary brachytherapy as a
tool for dosimetry.8 Aims of the study were (1) to
determine, by the use of dose-volume histograms, the dose distribution
of the ß-emitter 90Sr/90Y
along the coronary irradiated segment when delivered by a
noncentered device, (2) to establish the dose that could be
predictive of efficacy in intracoronary brachytherapy, and (3)
to determine the intravascular ultrasound (IVUS) predictors of the
plaque volume at 6-month follow-up of coronary segments treated
with balloon angioplasty (BA) followed by ß-radiation therapy. |
Methods |
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Patient Selection
Eighteen consecutive patients with single de novo coronary stenosis successfully treated with BA followed by intracoronary ß-radiation therapy were included in the study. Patients receiving a stent were excluded from the analysis. ß-Radiation was delivered according to the Beta Energy Restenosis Trial 1.5. The isotope selected was the pure ß-emitting 90Sr/90Y, and patients were randomly assigned to receive 12, 14, or 16 Gy at 2 mm from the source axis. The inclusion and exclusion criteria of this trial have been previously reported.9 The delivery of the radiation was performed by the use of the Beta-Cath System (Novoste Corp).10 The radiation source train of this system consists of a series of 12 independent 2.5-mm-long cylindrical seeds that contain the 90Sr/90Y sources and is bordered by 2 gold radiopaque markers at distal and proximal parts separated by 30 mm.10
IVUS Analysis
The treated coronary segment was evaluated by means of
3D IVUS imaging, which allowed volumetric calculations of the
irradiated area. The selection of the area of interest has been
reported elsewhere.11 In brief, a few steps were followed:
First, an angiogram was performed after positioning the delivery
catheter and the relation between anatomic landmarks and the 2 gold
markers were documented. The anatomic landmark closest to either of the
gold markers was used as a reference point. This angiographic reference
point was identified during a contrast injection with the IVUS imaging
element at the same position as the gold marker of the source. The
image from the IVUS imaging element was recorded and the reference
point identified. During the subsequent pullback, this reference point
was recognized and used for selecting the area subject to the
analysis: 30 mm for the irradiated segment.12
The system used for imaging was a mechanical IVUS system (ClearView,
CVIS, Boston Scientific Corp) with a sheath-based IVUS catheter
incorporating a 30-MHz, single-element transducer rotating at 1800 rpm
(Ultracross, CVIS). The transducer is placed inside a 2.9F, 15-cm-long
sonolucent distal sheath that alternatively houses the guide wire
(during the catheter introduction) or the transducer (during imaging).
The IVUS transducer was withdrawn through the stationary imaging sheath
by an ECG-triggered pullback device with a stepping
motor.12 The ECG-gated image acquisition and digitization
was performed by a workstation designed for the 3D reconstruction of
echocardiographic images12 (EchoScan,
Tomtec). Description of this system has been previously reported in
detail.12 13 14 In brief, the steering logic of the
workstation considered the heart rate variability and only acquired
images from cycles meeting a predetermined range and coinciding with
the peak of the R wave. If an R-R interval failed to meet the preset
range, the IVUS catheter remained at the same site until a cardiac
cycle met the predetermined R-R range. The IVUS transducer then was
withdrawn 0.2 mm to acquire the next image.12 13 14
This system ensures the segment-to-segment independence by avoiding
taking images during the axial movement of the IVUS catheter that
occurs during the cardiac cycle. Given the slice thickness of 0.2
mm and the length subject to the analysis of 30 mm
(distance between the 2 gold markers of the radiation source), 150
cross-sectional images per segment were digitized and analyzed.
A semiautomatic contour detection program was used for the 3D
analysis.15 This program constructs 2 longitudinal
sections from the data set and identifies the contours corresponding to
the lumen-intima and media-adventitia boundaries. Corrections could be
performed interactively by "forcing" the contour through visually
identified points; the entire data set then was updated.15
Careful checking and editing of the contours of the 150 planar images
was performed with an average of 45 minutes for complete evaluation.
The area encompassed by the lumen-intima and media-adventitia
boundaries defined the luminal and the total vessel volumes,
respectively. The difference between total vessel and luminal volumes
defined the plaque volume. Because media thickness cannot be measured
accurately, we assumed that the plaque volume included the
atherosclerotic plaque and the media.16 Volumetric data
were calculated by the formula
V=
ni=1Ai
· H, where V=volume, A=area of total vessel or lumen or plaque in a
given cross-sectional ultrasound image, H=thickness of the
coronary artery slice that is reported by this digitized
cross-sectional IVUS image, and n=the number of digitized
cross-sectional images encompassing the volume to be
measured.15 At follow-up, meticulous matching of the
region of interest was performed by comparing the longitudinal
reconstruction with that after treatment as previously
described11 (Figure 1
). The
feasibility and intraobserver and interobserver variability of this
system have been previously reported.11 13 17 18 For the
purposes of the study, the computed volume of the irradiated segment
was divided into 2-mm-long subsegments. Since the irradiated segment
measured 30 mm, 15 subsegments were defined per patient, each of
them with 10 IVUS cross sections (0.2 mm per cross section). All
individual cross sections were studied by 2 investigators, blinded to
the dosimetry results. Type of plaque and the presence of dissection
were qualitatively assessed. Type of plaque was defined in every cross
section as intimal thickening, soft, fibrous, mixed, and diffuse
calcified according to the guidelines previously
reported.19 Intimal thickening was defined when the
thickness of the intima-media complex was <0.3 mm.19
Soft tissue was defined when 
80% of the cross-sectional area was
constituted by material showing less echoreflectivity than the
adventitia, with an arc of calcium <10°, fibrous plaque when the
echoreflectivity of 80% of the material was as bright as or brighter
than the adventitia without acoustic shadowing, diffuse calcified
plaque when it contained material brighter than the adventitia showing
acoustic shadowing in >90°, and mixed when the plaque did not match
the 80% criterion.19 We categorized the 2-mm-long
subsegments as normal/intimal thickening, soft, hard (fibrous and
mixed), and diffuse calcified when 80% of the cross sections within
the subsegment were of the same type. In those cross sections
containing up to 90° of calcium arc, the contour of the external
elastic membrane was imputed from noncalcified slices. Dissection of
the vessel was defined as a tear parallel to the vessel
wall.19 Changes in luminal, plaque, and total vessel
volume between immediately after treatment and at follow-up were also
computed per subsegment. Those subsegments in which the origin of side
branches involved >90° of the circumferential arc in >50% of the
cross sections or were defined as diffuse calcified were excluded from
the analysis.
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Dose Calculation
The actual dose received by the vessel was retrospectively
calculated by means of dose-volume histograms7 in every
2-mm-long subsegment. This method is based on quantitative IVUS under
the assumption that the radiation source is positioned at the same
place as the IVUS catheter.8 The distance between the
center of the catheter and media-adventitia interface was calculated in
24 pie slices (15°) in all cross sections corresponding to the
irradiated area.9 Considering the prescribed dose and the
accurate geometric data obtained from the IVUS, the cumulative curve of
the dose-volume histogram for a predefined volume (ie, adventitia as
calculated at 0.5 mm outside the external elastic membrane) can be
obtained (Figure 2). From this curve, the
minimum dose received by 90% of the adventitial volume
(Dv90Adv) was calculated. The methodology and
feasibility of this dosimetry approach in vascular brachytherapy has
been previously reported.8
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Statistical Analysis
Data are presented as mean±SD or proportions.
Differences in quantitative IVUS data between the types of tissue were
assessed by means of 1-way ANOVA. Differences in quantitative IVUS data
between subsegments with and without dissection and with and without
calcium were evaluated by the use of an unpaired Student’s
t test. To determine the relation between the dose received
by the adventitia and the plaque volume at follow-up, linear regression
analysis was performed first. Then, nonlinear components were
added to the equation (x-1 and
x-2 were added to describe the steep increase of
plaque volume at low dose). These components were included in the model
if they described the relation significantly better. Finally, the model
was corrected for the plaque volume after treatment. Multivariable
regression analyses were performed to identify independent
predictors of plaque volume at follow-up among IVUS-derived (types of
tissue, dissection, and plaque volume after treatment) and dosimetric
variables (Dv90Adv). All tests were 2-tailed,
and a value of P<0.05 was considered statistically
significant.
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Results |
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Baseline Characteristics
Two hundred seventy subsegments were defined in 18 patients successfully treated with BA followed by intracoronary brachytherapy. Sixty-four subsegments were excluded from the final analysis because of either diffuse calcified plaque that precluded the quantification of the total vessel volume (n=30) or side branches that involved >90° of the circumferential arc in >50% of the cross sections (n=34). Therefore, 206 irradiated subsegments were the subject of the study. Fifty-five (27%) subsegments were defined as soft, 129 (62%) as hard, and 22 (11%) as normal/intimal thickening. Dissection was observed in 34 (16.5%) subsegments.
Volumetric Changes and Dosimetry
On average, total vessel volume increased at follow-up
(32.5±9 mm3 after treatment to
35.5±11 mm3 at follow-up;
P<0.0001), accommodating a parallel increase in plaque
volume (15.3±6 to 18.3±7 mm3;
P<0.0001). As a result, mean luminal volume remained
unchanged (17.1±7 to 17.0±7 mm3;
P=NS). Subsegments with hard tissue demonstrated less
increase in plaque, resulting in an increase in luminal volume as
compared with soft and normal/intimal thickening subsegments (Figure 3). The behavior of those hard
subsegments containing mixed calcified tissue (up to 90°; n=104) was
compared with those containing mixed noncalcified tissue (n=25). Mean
changes in plaque and total vessel volumes were comparable (
plaque
[mm3]: +1.3±4.2 in mixed calcified vs
+1.8±5.2 in mixed noncalcified; P=NS; total vessel
volume [mm3]: +2.6±6.2 in mixed calcified vs
+4.2±5.8 in mixed noncalcified; P=NS), resulting in a
comparable mean increase in luminal volume at follow-up (+1.3±5.2
mm3 in mixed calcified vs +1.9±5.7
mm3 in mixed noncalcified; P=NS).
Dissected subsegments demonstrated a trend toward a smaller increase in
plaque as compared with nondissected subsegments (+1.2±3 vs
+3.3±6 mm3; P=0.08). The mean of
all 3 prescribed doses at 2 mm from the source was 14±1.8 Gy. The
calculated Dv90Adv was 5.5±2.5 Gy (range 0.2 to
12.4). A wide range of dose distribution was observed in the irradiated
coronary subsegments (Figure 4).
The association between Dv90Adv with the plaque
volume at follow-up is depicted in Figure 5. The model appeared to follow a
polynomial equation with linear and nonlinear components. Nonlinear
components described the increase in plaque volume at lower doses,
whereas the residual plaque volume after treatment accounted for the
linear relation of the curve. Changes in plaque volume appeared to
decrease with dose (Figure 6). Four Gray
was the minimum effective dose to be delivered to 90% of the
adventitia because subsegments receiving at least this dose
demonstrated a significantly smaller increase in plaque volume as
compared with those receiving <4 Gy (P<0.001). As a
result, luminal volume decreased significantly less in those
subsegments receiving 4 Gy and even increased when the minimal dose
to the adventitia was >6 Gy. Multivariable regression
analyses identified plaque volume after treatment as a positive
predictor of plaque volume at follow-up, whereas
Dv90Adv and type of plaque (hard) were negative
predictors (Table).
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Discussion |
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This study demonstrates for the first time the relation between plaque increase, as assessed by IVUS, and the dose received by the adventitia, as calculated by means of dose-volume histograms. A plot of dose-volume histogram is a standard method used in radiotherapy that condenses the large body of information available from conventional 3D distribution data into a plot summarizing graphically the radiation distribution throughout the target volume.7
The assumption of the adventitia as the target tissue is supported by experimental studies.20 21 Scott et al20 localized the proliferating cells in the adventitia and their migration into the neointima after angioplasty by using bromodeoxyuridine immunohistochemistry. Similarly, Waksman et al21 demonstrated a greater cell proliferation in control vessels 3 days after angioplasty in the adventitia at the site of the medial tear as compared with the medial wall in the same region. In this study, the proliferation was significantly reduced in irradiated vessels with either a source of 90Sr/90Y or 192Ir that delivered 14 or 28 Gy at 2 mm into the artery wall.21
The actual dose received by the adventitia appeared to be rather low as
compared with the prescribed dose at 2 mm from the source.
Furthermore, the dose varied considerably between coronary
subsegments, as demonstrated by the dose distribution depicted in the
Figure 4
. The use of ß-radiation may account in part for this
dose inhomogeneity. As compared with -radiation, ß-sources have
more fall-off because of the short range of electrons.6
This feature may become crucial when treating vessels with a great
degree of vessel tapering or, alternatively, lesions showing positive
remodeling where the distance from the source to the surrounding
adventitia may be smaller or greater than expected. In this regard, the
use of IVUS as a tool for dosimetry in ß-radiation therapy may become
mandatory.
Dose uniformity also may be influenced by the source centering in the lumen.22 By the use of dose-volume histograms, Carlier et al8 demonstrated in 10 patients treated with balloon angioplasty followed by intracoronary ß-radiation that the prescribed dose was administered in only 35% of the adventitia. After centering the source in the lumen, up to 60% of the adventitia may have received this dose.
The remnant plaque burden at the site of angioplasty becomes a powerful predictor of the outcome. This is in accordance with other studies that identified, either in nonstented or stented coronary segments, postintervention cross-sectional area as a predictor of restenosis.23 24 In this regard, the usefulness of a debulking technique before radiation therapy should be addressed in further studies.
Dv90Adv was also identified as an independent
predictor of the plaque volume at follow-up. The relation between
Dv90Adv and plaque volume at follow-up appeared
to be polynomial with linear and nonlinear components. This may model
the survival curve of mammalian cells.25 The minimal
effective dose to be delivered to 90% of the adventitial volume
appeared to be 4 Gy. Further increase in dose resulted in net increase
in luminal volume at follow-up. Similarly, in a subgroup
analysis of the SCRIPPS trial, late loss was significantly
lower when the entire circumference of the adventitial border was
exposed to 8 Gy.26 Radiation doses >20 Gy have been
suggested to be able to completely eliminate the smooth muscle cell
population from the treated area.27 However, because cells
from normal tissue have a limited capacity to
proliferate,28 lower doses probably would be sufficient to
permanently prevent restenosis.
Finally, subsegments containing hard tissue (fibrotic and calcified material up to 90° of the circumferential arc) demonstrated a trend to be a negative predictor of plaque volume at follow-up. Hard plaque on IVUS consists of a more mature tissue with low cellularity and high content of extracellular matrix.29 30 These features may induce either a physical barrier for migration of smooth muscle cells from the surrounding layers or a reduced capacity to proliferate when injured as compared with that of the soft tissue with a high concentration of smooth muscle cells.29 30 31 Further, it is hypothesized that tissue composition may potentially exert a different degree of shielding effect on radiation and thus become less effective. However, the degree of remodeling was similar between the different types of tissue, suggesting that the effects of attenuation of radiation induced by hard material (either containing calcium up to 90° of circumferential arc or mixed noncalcified tissue) may be negligible as compared with that of soft tissue.
Study Limitations
We assumed that the IVUS and the delivery catheters were lying in
the same position in the treated coronary segment. The size of
the IVUS catheter is smaller (2.9F) than the brachytherapy device (5F),
which is thus to some extent more centered in the lumen. Although the
catheters should be on the shortest 3D path in the lumen,
coronary arteries have a complex curved geometry in space and
can be partially deformed by the catheters. Thus, catheters with
different rigidity may occupy different positions. The development of
new systems incorporating the IVUS imaging element on the delivery
catheter might resolve this drawback.
During irradiation, the position of the delivery catheter inside the lumen is not fixed and may vary along the cardiac cycle because of ventricular contractions, which may lead to some degree of inhomogeneity not assumed by data derived from the static end-diastolic IVUS images.
The behavior of diffuse calcified plaques after radiotherapy has not been evaluated because the acoustic shadowing would have impeded the reliable analysis of total vessel and plaque volumes.19
It has not been possible to differentiate those areas that have been traumatized and irradiated from those only irradiated. Thus, no conclusions regarding the effect on radiation in irradiated but noninjured segments can be drawn. Further studies will address this problem by defining meticulously the injured and the irradiated areas either on IVUS or quantitative coronary angiography.
Finally, the dose as presented by the use of dose-volume histograms is not a direct measurement. The theoretical value obtained at the level of the adventitia is derived from the fall-off of the isotope and the geometrical data obtained from the IVUS study. The influence of the attenuation of the radiation caused by different tissue characteristics has not been taken into consideration. Future investigations should address the implementation of a dosimetry program on-line to prescribe the radiation dose in a more refined fashion.
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Acknowledgments |
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Dr Kay was supported by The National Heart Foundation of New Zealand. The Wenckebach prize was awarded to Dr Serruys by the Dutch Heart Foundation for brachytherapy research in the catheterization laboratory.
Received September 22, 1999; revision received November 23, 1999; accepted December 22, 1999.
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Y. Morino, H. Kaneda, T. Fox, A. Takagi, A. H.M. Hassan, R. Bonan, I. Crocker, A. J. Lansky, W. K. Laskey, M. Suntharalingam, et al. Delivered Dose and Vascular Response After {beta}-Radiation for In-Stent Restenosis: Retrospective Dosimetry and Volumetric Intravascular Ultrasound Analysis Circulation, October 29, 2002; 106(18): 2334 - 2339. [Abstract] [Full Text] [PDF]
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 A. Maehara, N. S. Patel, L. B. Harrison, N. J. Weissman, A. B. Bui, H.-S. Kim, A. E. Ajani, M. T. Castagna, T. L. McMillan, N. Yang, et al. Dose heterogeneity may not affect the neointimal proliferation after gamma radiation for in-stent restenosis: A volumetric intravascular ultrasound dosimetric study J. Am. Coll. Cardiol., June 19, 2002; 39(12): 1937 - 1942. [Abstract] [Full Text] [PDF]
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C. Hanefeld, S. Amirie, D. Borchardt, P. Grewe, K.-M. Muller, M. Kissler, and A. Mugge Dosimetric Measurements in Isolated Human Coronary Arteries: Comparison of Commercially Available Iridium192 With Strontium/Yttrium90 Emitters Circulation, May 28, 2002; 105(21): 2493 - 2496. [Abstract] [Full Text] [PDF]
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 K. Kozuma, M.A. Costa, W.J. van der Giessen, M. Sabate, J.M.R. Ligthart, V.L.M.A. Coen, I.P. Kay, A.J. Wardeh, A.H.M. Knook, P.J de Feyter, et al. Initial observation regarding changes in vessel dimensions after balloon angioplasty and stenting followed by catheter-based {beta}-radiation. Is stenting necessary in the setting of catheter-based radiotherapy? Eur. Heart J., April 2, 2002; 23(8): 641 - 649. [Abstract] [Full Text] [PDF]
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P. Wexberg, C. Kirisits, M. Gyongyosi, M. Gottsauner-Wolf, M. Ploner, B. Pokrajac, R. Potter, and D. Glogar Vascular morphometric changes after radioactivestent implantation: a dose-response analysis J. Am. Coll. Cardiol., February 6, 2002; 39(3): 400 - 407. [Abstract] [Full Text] [PDF]
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P.W. Serruys, D.P. Foley, M. Pieper, J.A. Kleijne, and P.J. de Feyter on behalf of the TRAPIST investigators The TRAPIST Study. A multicentre randomized placebo controlled clinical trial of trapidil for prevention of restenosis after coronary stenting, measured by 3-D intravascular ultrasound Eur. Heart J., October 2, 2001; 22(20): 1938 - 1947. [Abstract] [PDF]
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G. S. Mintz, N. J. Weissman, and P. J. Fitzgerald Intravascular Ultrasound Assessment of the Mechanisms and Results of Brachytherapy Circulation, September 11, 2001; 104(11): 1320 - 1325. [Full Text] [PDF]
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J. M. Ahmed, G. S. Mintz, R. Waksman, R. Mehran, B. Leiboff, A. D. Pichard, L. F. Satler, K. M. Kent, and N. J. Weissman Serial Intravascular Ultrasound Assessment of the Efficacy of Intracoronary {gamma}-Radiation Therapy for Preventing Recurrence in Very Long, Diffuse, In-Stent Restenosis Lesions Circulation, August 21, 2001; 104(8): 856 - 859. [Abstract] [Full Text] [PDF]
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J. M. Ahmed, G. S. Mintz, R. Waksman, N. J. Weissman, B. Leiboff, A. D. Pichard, L. F. Satler, K. M. Kent, and M. B. Leon Serial Intravascular Ultrasound Analysis of the Impact of Lesion Length on the Efficacy of Intracoronary {{gamma}}-Irradiation for Preventing Recurrent In-Stent Restenosis Circulation, January 16, 2001; 103(2): 188 - 191. [Abstract] [Full Text] [PDF]
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 M A Costa, K Kozuma, A L Gaster, W J van der Giessen, M Sabaté, D P Foley, I P Kay, J M R Ligthart, P Thayssen, M J van den Brand, et al. Three dimensional intravascular ultrasonic assessment of the local mechanism of restenosis after balloon angioplasty Heart, January 1, 2001; 85(1): 73 - 79. [Abstract] [Full Text]
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P.W. Serruys and S.G. Carlier Brachytherapy in the Journal: European cardiologists have their own forum and should use it! Eur. Heart J., December 2, 2000; 21(24): 1994 - 1996. [PDF]
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K Kozuma, M.A Costa, M Sabate, C.J Slager, E Boersma, I.P Kay, J.P.A Marijnissen, S.G Carlier, J.J Wentzel, A Thury, et al. Relationship between tensile stress and plaque growth after balloon angioplasty treated with and without intracoronary beta-brachytherapy Eur. Heart J., December 2, 2000; 21(24): 2063 - 2070. [Abstract] [PDF]
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I. P. Kay, M. Sabate, M. A. Costa, K. Kozuma, M. Albertal, W. J. van der Giessen, A. J. Wardeh, J. M. R. Ligthart, V. M. A. Coen, P. C. Levendag, et al. Positive Geometric Vascular Remodeling Is Seen After Catheter-Based Radiation Followed by Conventional Stent Implantation but Not After Radioactive Stent Implantation Circulation, September 19, 2000; 102(12): 1434 - 1439. [Abstract] [Full Text] [PDF]
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