The role of radiation therapy in the management of vascular restenosis. Part I. Biologic basis

Liquid (188)Re-filled balloon dilation for the treatment of refractory benign airway strictures: preliminary experience

PURPOSE

To present the preliminary results of beta irradiation with use of liquid rhenium 188 ((188)Re)-filled balloon dilation in the treatment of refractory benign airway strictures.

MATERIALS AND METHODS

Ten sessions of beta irradiation by using liquid (188)Re-filled balloon dilation were prospectively performed in nine patients with refractory bronchial strictures between 2003 and 2006. Indications for treatment were dyspnea caused by repeat stricture or no response to previous treatment (ie, balloon dilation and/or temporary stent placement or laser therapy) in seven patients and dyspnea caused by exuberant granulation tissue formation at the distal end of the placed stent in two. To assess the treatment efficacy, the authors calculated and compared the mean intervals of interventional treatments before and after dilation with (188)Re and mercaptoacetyltriglycine (MAG(3))-filled balloons.

RESULTS

Liquid (188)Re-filled balloon dilation was successfully performed in all nine patients, with no procedure-related complications. Immediately after the procedure, all patients showed resolution of their dyspnea. Five patients remained asymptomatic at 5-25-month follow-up. Four patients experienced dyspnea caused by recurrent stricture 1-10 months after dilation. The mean intervals between interventional treatments increased significantly from 3.1 months +/- 2.1 before (188)Re-MAG(3)-filled balloon dilation to 10.8 months +/- 8.8 after (188)Re-MAG(3)-filled balloon dilation in all nine patients (Wilcoxon signed rank test, P = .025).

CONCLUSIONS

beta irradiation with liquid (188)Re-filled balloon dilation can be safely used for refractory benign airway strictures. A large study with longer follow-up is needed to draw a definite conclusion.

Rhenium-188 Mercaptoacetyltriglycine–filled Balloon Dilation in the Treatment of Recurrent Urethral Strictures: Initial Experience with Five Patients

PURPOSE

To evaluate the efficacy of beta-irradiation therapy with use of a rhenium-188 mercaptoacetyltriglycine ((188)Re-MAG(3))-filled balloon for the prevention of restenosis in urethral strictures refractory to repetitive surgical or interventional procedures.

MATERIALS AND METHODS

Five male patients with traumatic (n = 4) or postoperative anastomotic (n = 1) recurrent urethral strictures were included. One to four sessions of 20-30 Gy beta-irradiation at a 1-mm tissue depth with (188)Re-MAG(3)-filled balloon dilation were undertaken in each patient.

RESULTS

No procedural complications or toxicities were noted. During the mean follow-up period of 16.2 months, the stricture did not recur in two patients, whereas three patients required additional interventional procedures. In two of these patients, the treatment intervals between the required sessions were significantly prolonged. For the entire group, the mean treatment interval was prolonged from 2.2 months before (188)Re-MAG(3)-filled balloon dilation to 10.7 months after therapy.

CONCLUSION

(188)Re-MAG(3)-filled balloon dilation shows promise in preventing or delaying stricture recurrence in patients with recurrent urethral strictures.

Reduction of Tissue Hyperplasia with a Rhenium188 Mercaptoacetyltriglycine-3–filled Balloon: Preliminary Study in a Canine Urethral Model

PURPOSE

To evaluate the efficacy of beta-radiation therapy with rhenium-188 mercaptoacetyltriglycine-3 (MAG(3))-filled balloons to reduce tissue hyperplasia secondary to stent placement in 18 canine urethras.

MATERIALS AND METHODS

Eight dogs were treated with 188-Re MAG(3)-filled balloon dilation immediately after stent placement and were killed 4 weeks later (group I, n = 4) or 8 weeks later (group II, n = 4). Five dogs were treated with 188-Re MAG(3)-filled balloon dilation 2 weeks after stent placement and were killed 4 weeks after stent placement (group III). The remaining five dogs were treated with conventional balloon dilation immediately after stent placement and were killed 4 weeks later; these animals formed the control group (group IV). Retrograde urethrography (RUG) was performed during follow-up and three histologic parameters were investigated: the number of epithelial layers, papillary projection thickness, and degree of submucosal inflammatory cell infiltration. The areas inside and outside the ends of the stents were evaluated in each case after animal sacrifice. After testing statistical significance of data for RUG and histologic findings in the four study groups, the Mann-Whitney U test was used to compare groups I and II to determine delayed effects of irradiation, groups I and III to determine benefits of delayed irradiation, groups I and IV to determine efficacy of immediate irradiation for reducing tissue hyperplasia, and groups III and IV to determine efficacy of delayed irradiation for reducing tissue hyperplasia.

RESULTS

There were no significant differences in the four study groups on RUG before animal sacrifice. Between groups I and II, group II showed significantly lower mean values in five of six histologic comparisons. Between groups I and III, group III showed significantly lower mean values in only papillary projection thickness inside the stent ends. Between groups I and IV, group I showed significantly lower mean values in all three histologic parameters outside the stent ends. Between groups III and IV, group III showed significantly lower mean values in only two histologic parameters (papillary projection thickness in the in-stent area and inflammatory cell infiltration outside the stent edges).

CONCLUSION

beta-Irradiation with use of a 188-Re MAG(3)-filled balloon shows the potential to reduce tissue hyperplasia secondary to stent placement in a canine urethral model. Treatment with 188-Re MAG(3)-filled balloons at the time of stent placement shows not only favorable outcomes for reducing tissue hyperplasia but also improved delayed effects until 8 weeks.

Prevention of intimal hyperplasia

OBJECTIVE

Endovascular brachytherapy, delivered by a variety of catheter-based devices, has proven clinically effective for the inhibition of neointimal hyperplasia (NIH) after coronary and peripheral balloon/stent angioplasty. No platform, however, has been developed to deliver low-dose radiation in concert with vascular surgical operations. The purpose of this study was to evaluate the vascular response following balloon injury to the rabbit carotid artery, with and without topical low-dose 45Ca, applied by an external vascular "wrap".

METHODS

Twelve rabbit carotid arteries were subjected to balloon injury by embolectomy catheter. The common carotid artery was then "wrapped" circumferentially with a biostable polyurethane membrane (Nanoskin Secant Medical, Perkasie, PA), without radiation (n = 6), or with radiation (n = 6) (45Ca approximately 50 microCi). The animals were sacrificed at 4 weeks for histologic assessment of the treated vessels.

RESULTS

The 45Ca wrap inhibited NIH evidenced by trends towards reduction of intimal area (0.46 +/- 0.19 control carotid vs. 0.35 +/- 0.15 (45)Ca-treated carotid arteries; P = .11), maximal intimal thickness (0.21 +/- 0.08 vs. 0.16 +/- 0.05; P = .12), average intimal thickness (0.12 +/- 0.06 vs. 0.08 +/- 0.03; P = .08), marginally significant reduction in percent area stenosis (33 +/- 15% vs. 21 +/- 9%; P = .06) and marked neointima suppression in areas immediately adjacent to 45Ca wrap remnants. Medial necrosis (P = .003), however, was observed slightly more for 45Ca-treated carotid arteries versus control arteries.

CONCLUSION

Low-dose 45Ca beta-radiation labeled onto a polyurethane membrane appears to inhibit NIH in an animal model.

External beam radiation for prevention of intimal hyperplasia in peripheral arterial bypasses

PURPOSE

Neointimal hyperplasia is one of the limiting factors in infrainguinal prosthetic vascular grafting. We conducted a pilot study to assess the possible role of radiotherapy for the prevention of this proliferating cellular process.

METHODS AND MATERIALS

Ten patients (7 men, 3 women; median age: 73 years) suffering from critical leg ischemia were treated by infrainguinal revascularization using 6-mm polytetrafluoroethylene. Postoperative radiation therapy of the anastomotic sites started within 24 h. A dose of 20.4 Gy was delivered in 12 fractions in 2.5 weeks by external beam radiation with electrons. The target volume was defined as the clip-marked anastomotic region plus a 1.5-cm safety margin in each direction.

RESULTS

Radiation therapy was technically feasible in all cases without radiation-related side effects. In one patient, radiotherapy had to be terminated prematurely, because of a hematoma at the distal anastomotic site with consequent skin necrosis. One patient developed an occlusion of a suprainguinal graft without anastomotic stenosis after 9 months; 2 other grafts occluded at 12-month intervals. At a median follow-up of 16 months, the remaining 6 patients had no signs of restenosis.

CONCLUSIONS

The restenosis rate of peripheral vascular grafts after external beam radiation was lower than expected without additional treatment. The value of this approach will now be determined in a randomized prospective trial.

Delayed re-endothelialization and T-cell infiltration following intracoronary radiation therapy in the porcine model

PURPOSE

To evaluate the late induction of apoptosis following intracoronary radiation (IR) and the effects of IR on inflammatory cells.

METHODS AND MATERIALS

Porcine coronaries were injured by balloon overstretch followed by either 0 or 15 Gy of 192Ir prescribed to 2 mm from the center of the source. Swine were euthanized at 3, 7, and 14 days posttreatment, and arteries were stained for markers of smooth muscle cells (SMCs alpha-actin), T cells (CD3), macrophages, endothelial cells, and apoptotic nuclei (terminal uridine nick end labeling, TUNEL). Intimal area (IA) and IA corrected for medial fracture length (IA/FL) were quantified by digital image analysis, which was also used to quantify the distribution of immunostain-positive cells in the adventitia, media, and neointima, respectively.

RESULTS

IA/FL was significantly reduced following treatment with 15 Gy, in association with decreased SMC density. Following injury and IR, TUNEL- and CD3-positive cell density increased significantly, and density of macrophages was increased in the adventitia and neointima. Staining for endothelial cells revealed a delay of re-endothelialization after radiation treatment.

CONCLUSION

Increased T-cell infiltration at the medial tear following IR, perhaps due to incomplete re-endothelialization, may indicate incomplete healing. The elevated apoptosis of these infiltrating T cells may indicate a mechanism for the resolution of inflammation.

On the applicability of the AAPM TG-60/TG-43 dose calculation formalism to intravascular line sources: proposal for an adapted formalism

Despite the widely recognized usefulness of the AAPM TG-43 brachytherapy dose calculation formalism, a straightforward application of this approach to describe the dose distribution about intravascular line sources as proposed by TG-60 may be difficult or even impossible, especially when these line sources emit low-energy photons or beta particles. The causes of these limitations are investigated and illustrated by means of some numerical examples. In order to solve the observed limitations an adapted formalism is proposed, intended specifically for the description of the dose rate distribution about line sources but conceptually similar to the TG-43/TG-60 formalism. Several examples are presented to illustrate the usefulness of the proposed line source dose calculation formalism.

Kinetics of release of heparin from alginate hydrogel

PURPOSE

Injected sodium alginate may be a useful perivascular drug delivery vehicle. This study was performed to determine the release rates of heparin from sodium alginate hydrogels cross-linked with varying amounts of calcium gluconate.

MATERIALS AND METHODS

Six hydrogels, composed of 0.16 mEq sodium alginate and 4,000 units unfractionated heparin, were cross-linked with calcium gluconate to yield ion equivalence (IE) ratios (calcium:alginate) of 0.2, 0.4, 0.58, 0.8, 1.0, or 1.2. Two milliliters of normal saline was placed on top of each gel and allowed to remain in contact for up to 10 days. At set time intervals, the amount of heparin in the eluent was determined with use of high-performance liquid chromatography.

RESULTS

Gels with 0.2 and 0.4 IE were partially liquid at 24 hours; the other gels solidified within 10 minutes. The 0.58 IE gel was slowest to solidify but immobilized the most heparin and released heparin slowest over 10 days. At 10 days, between 5.5% and 9.8% of the heparin immobilized was retained in the gel.

CONCLUSION

This hydrogel shows promise as a vehicle for in vivo perivascular heparin delivery. The 0.58:1 IE ratio hydrogel has slowest release rate and the greatest immobilization despite its longer cross-linking time.

Radiolabeling brachytherapy sources with Re-188 through chelating microfilms: stents

Rhenium-188 (Re-188, T(1/2) = 17 h) emits beta particles (E(max) = 2. 12 MeV) having an ideal range for intravascular brachytherapy and certain cancer brachytherapies. Re-188 was attached to metal wafers and stents via a chelating microfilm, and these brachytherapy sources characterized in vitro and in vivo. To prepare the sources, a siloxane film containing reactive amines was plasma deposited on the metal, a chelating microfilm conjugated to the amines, and the chelating microfilm used to attach Re-188. Re-188 was selectively bound to materials coated with the chelating microfilm. Binding correlated with the amount of radionuclide used. Wafers (1 cm(2)) bound up to 62.9 MBq (1.7 mCi) of Re-188 with yields generally near 30%. Stents bound up to 26.6 MBq (720 microCi). Typically, stents were labeled to bind 4-12 MBq and deposit 10-30 Gy at 2 mm in the arterial wall. In phantom studies, the longer nitinol stents deposited doses of 2.3 Gy/MBq (0.085 Gy/microCi), while shorter stainless steel stents deposited 4.62 Gy/MBq (0.171 Gy/microCi). After placement in arteries of pigs, only the Re-188-stents were detected by scintigraphy at times up to 24 h. Scintigraphy did not detect activity in other organs. Blood sampling (0.1-24 h) detected maximum radioactivity (up to 388 cpm/mL/100micro Ci) at 6 h. We conclude that on-demand radiolabeling of stents and other brachytherapy sources with Re-188 can be performed routinely.

Modelling of a 188W/188Re beta line source for coronary brachytherapy by means of EGS4 Monte Carlo simulations

In this paper, we present results from three different simulation models that are used to determine the dose distribution around a 188W/188Re coronary brachytherapy source with EGS4 Monte Carlo simulations. The three models are found to give similar results within 10%. Agreement was found with experimental data from measurements in a PMMA phantom. It has been shown that in the therapeutically relevant region the beta line source can be characterized by the radial depth-dose distribution in water.