The role of radiation therapy in the management of vascular restenosis. Part II. Radiation techniques and results

De Novo Femoropopliteal Stenoses: Endovascular Gamma Irradiation Following Angioplasty—Angiographic and Clinical Follow-up in a Prospective Randomized Controlled Trial

PURPOSE

To assess and report the follow-up results of a randomized controlled trial on centered endovascular gamma irradiation performed after percutaneous transluminal angioplasty (PTA) for de novo femoropopliteal stenoses.

MATERIALS AND METHODS

Thirty patients who underwent PTA for de novo femoropopliteal stenoses were randomly assigned to undergo 14-Gy centered endovascular irradiation (irradiation group, n = 15) or no irradiation (control group, n = 15). Intraarterial angiography was performed 6, 12, and 24 months after treatment; duplex ultrasonography (US), the day before and after PTA and 1, 3, 6, 9, 12, 18, and 24 months later. Treadmill tests and interviews were performed the day before PTA and 1, 3, 6, 9, 12, 18, and 24 months later. Results of angiography, duplex US, treadmill tests, and interviews were evaluated with the nonpaired t or the Fisher exact test.

RESULTS

Baseline characteristics did not differ significantly between the two groups. Mean absolute individual changes in degree of stenosis, compared with the degrees of stenosis shortly after PTA, in the irradiation group versus in the control group were -10.6% +/- 22.3 versus 39.6% +/- 24.6 (P <.001) at 6 months, -2.0% +/- 34.2 versus 40.6% +/- 32.6 (P =.002) at 12 months, and 7.4% +/- 43.2 versus 37.7% +/- 34.5 (P =.043) at 24 months. The rates of target lesion restenosis at 6 (P =.006) and 12 (P =.042) months were significantly lower in the irradiation group. The numbers of target lesion re-treatments were similar between the groups, but target vessel re-treatments were more frequent in the irradiation group. There were no significant differences in interview or treadmill test results between the two groups at t test analysis.

CONCLUSION

The degree of stenosis was significantly reduced 6, 12, and 24 months after angioplasty of de novo femoropopliteal stenoses in the patients who underwent endovascular irradiation.

Endovascular gamma irradiation of femoropopliteal de novo stenoses immediately after PTA: interim results of prospective randomized controlled trial

PURPOSE

To report an interim analysis of whether centered endovascular irradiation with the iridium 192 ((192)Ir) source immediately after percutaneous transluminal angioplasty (PTA) of de novo femoropopliteal stenoses lowers the restenosis rate.

MATERIALS AND METHODS

Thirty patients undergoing PTA to treat femoropopliteal stenoses were randomized for prophylaxis against restenosis with centered endovascular irradiation with a (192)Ir source (a dose of 14 Gy 2 mm deep to the vessel wall, irradiation group) or no irradiation (control group). Angiographic follow-up was available for 22 patients at 6 months (irradiation group, n = 10) and 12 patients at 12 months (irradiation group, n = 6). Duplex sonography, treadmill testing, and interviews were performed the day before and the day after PTA and after 1, 3, 6, 9, and 12 months. Results of angiography, duplex sonography, treadmill testing, and interviews were evaluated with a t test and multivariate analysis of variance (clinical characteristics, chi(2) test).

RESULTS

Baseline characteristics were comparable in the two groups. Interim analysis of the 6-month follow-up data revealed a trend toward a significantly lower restenosis rate in the irradiation group. The change in the degree of stenosis compared with that after PTA was -14.7% +/- 20.8 (mean +/- SD) in the irradiation group versus 37.7% +/- 27.3 in the control group (P =.001) and became even more marked at 12 months (-9.5% +/- 34.5 vs 45.5% +/- 40.7 [P =.03], respectively). The follow-up results of treadmill testing and interviews showed a nonsignificant benefit for the irradiation group. One thromboembolic complication occurred during irradiation. No side effects were observed during follow-up.

CONCLUSION

Endovascular irradiation with a centered (192)Ir source immediately after PTA of de novo femoropopliteal stenoses reduces the restenosis rate.

Endovascular gamma-irradiation to prevent recurrent femoral in-stent restenosis. A case report

We report about a patient with twice recurrence of femoral in-stent restenoses. Centered endoluminal gamma-irradiation with 192 iridium was performed immediately after the second stent recanalization. The irradiation dose was 14 Gy calculated at 2-mm depth of vessel wall. One-year follow-up demonstrates neither clinical nor angiographic evidence of restenosis.

Experimental and clinical evaluation of the PARIS centering catheter for delivery of endovascular gamma-irradiation of femoropopliteal stenoses

PURPOSE

To investigate the effect of aortic bifurcation and iliac geometry on centered endovascular irradiation (CEI) of femoropopliteal arteries and evaluate procedure-related complications.

MATERIALS AND METHODS

In an experimental tubing model, crossover delivery of the dummy wire by an afterloader using different sheaths (Type I: noncrossover; Type II: crossover, length 40 cm; Type III: crossover, length 65 cm) was examined at simulated angles between 20 degrees -100 degrees (aortic bifurcation) and 0 degrees -100 degrees (iliac vessels). In the clinical phase, 28 heparin-anticoagulated patients underwent percutaneous transluminal angioplasty (PTA) for femoropopliteal stenoses followed by CEI (192-iridium, 14 Gray at 2 mm depth of the vessel wall) delivered with the centering catheter (crossover from contralateral leg using a 65-cm-long 8F sheath in 13 patients, noncrossover from ipsilateral leg using a 10-cm 8F sheath in 15 patients). Measurement of the aortic bifurcation angle before advancement of the crossover sheath and rating of iliac artery tortuosity on both sides was retrospectively performed on angiograms. Fifteen controls received no post-PTA CEI.

RESULTS

Experimental delivery of the dummy wire was not possible at aortic angles less than 40 degrees with Type I, 60 degrees with Type II, and 30 degrees with Type III sheaths. Advancement of the centering catheter was possible in all patients. CEI failed in two patients with crossover (aortic angle <40 degrees ) and in one obese patient with antegrade approach because advancement of the dummy wire was impossible. Thromboembolism rate was 4.6% during irradiation (2.3% after PTA alone).

CONCLUSIONS

CEI in femoropopliteal arteries has a risk of procedure-related thromboembolic complications. Efficacy is affected by vessel geometry.

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.

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.

Brachytherapy optimal planning with application to intravascular radiation therapy

We have been studying brachytherapy planning with the objective of minimizing the maximum deviation of the delivered dose from prescribed dose bounds for treatment volumes. A general framework for optimal treatment planning is presented and the minmax optimization is formulated as a linear program. Dose rate calculations are based on the dosimetry formulation of the American Association of Physicists in Medicine, Task Group 43. We apply the technique to optimal planning for intravascular brachytherapy of intimal hyperplasia using ultrasound data and 192Ir seeds. The planning includes determination of an optimal dwell-time sequence for a train of seeds that deliver radiation while stepping through the vessel lesion. The results illustrate the advantage of this strategy over the common approach of delivering radiation by positioning a single train of seeds along the whole lesion.

Brachytherapy for the prevention of stenosis in a canine hemodialysis graft model: preliminary observations

PURPOSE

To determine whether gamma brachytherapy can prevent in-stent stenosis in hemodialysis grafts.

MATERIALS AND METHODS

Six-millimeter polytetrafluoroethylene arteriovenous grafts were created bilaterally in six dogs. After 1 month, Wallstents spanning the venous anastomosis were placed to accelerate restenosis. Gamma irradiation (12 Gy) was delivered endoluminally to one of the two grafts by using an iridium 192 source; thus, each animal served as its own control. Fistulography was performed monthly for 10 months or until graft thrombosis, with measurement of stenosis at each time point. At the conclusion of the study period, the treated area was examined histologically, and a computer model was used to calculate the volume of intimal hyperplasia.

RESULTS

Delayed stent migration resulted in exclusion of one dog. In the remaining five dogs; maximum stenosis across all time intervals was less for the treated side (P < .04), and the volume of intimal hyperplasia was less for the treated side (P < .045). In one animal studied at 1 year, this trend reversed in terms of percentage stenosis but not total neointimal volume.

CONCLUSION

Brachytherapy with 192Ir (gamma) delivered at the time of stent placement reduces restenosis in this hemodialysis graft model, but, depending on the parameter evaluated (stenosis vs total volume of neointima), the benefit may wane or even reverse with time.

Supplemental oxygen does not synergize with intracoronary radiation for the prevention of restenosis in porcine coronary arteries

PURPOSE

Recurrence of obstructive coronary arterial lesions (restenosis) after angioplasty remains a significant clinical problem. Ionizing radiation, at doses >10 Gy administered locally to the angioplasty site, has been shown to inhibit restenosis in porcine coronary arteries, but lower doses are ineffective. Methods that will allow delivery of lower doses of radiation while retaining the antirestenotic efficacy observed at the higher doses are desirable. Hypoxic cells are known to be radioresistant; accordingly, we hypothesized that increasing blood oxygenation through the use of the TherOx Aqueous Oxygen system would lower the doses of endovascular radiation required for the prevention of restenosis.

MATERIALS AND METHODS

Five swine were studied as follows: balloon injury + oxygen alone was performed in two swine. Each swine had a balloon overstretch injury in two arteries, left anterior descending (LAD) and either right coronary artery (RCA) or left circumflex (LCX) artery (three arteries total). Balloon injury + oxygen followed by intracoronary irradiation was performed in a further three swine (six arteries). Controls consisted of arteries treated with 0, 5, or 15 Gy of 192Ir alone.

RESULTS

Arteries treated with the TherOx Aqueous Oxygen system alone were indistinguishable from arteries treated without oxygenation except for a larger adventitial area (5.29 +/- 0.20 vs. 2.77 +/- 0.28 mm2; p < 0.05). Arteries treated with the TherOx Aqueous Oxygen system along with 5 Gy of 192Ir exhibited a greater injury-corrected intimal area than arteries treated with radiation alone (0.76 +/- 0.18 vs. 0.33 +/- 0.08 mm2; p < 0.05). Neither thrombosis rate nor thrombus area was significantly different in arteries receiving the TherOx Aqueous Oxygen as compared with controls.

CONCLUSIONS

The TherOx Aqueous Oxygen system is safe in the context of balloon overstretch injury, but decreases the antirestenotic efficacy of 5 Gy of 192Ir. These findings suggest that hypoxia does not seem to be a major contributor to the dose of radiation required for suppression of neointima, at least when using noncentered gamma radiation delivery systems.