Intravascular ultrasound analysis of beta radiation therapy for diffuse in-stent restenosis to inhibit intimal hyperplasia

Calibration of the photon component of 198Au stents

PURPOSE

198Au has promising characteristics for radioactive stent material, having properties as a mixed beta-particle and gamma emitter. Calibration of these radioactive stents is required to provide accurate clinical dosimetry.

METHODS AND MATERIALS

We have developed an electroplating technique to incorporate stable gold onto stents followed by activation to 198Au in the University of Wisconsin nuclear reactor. The calibration method is a modification of the NIST traceable, in-air calibration technique for high-dose-rate (HDR) 192Ir sources.

RESULTS

The air-kerma strength of HDR and low-dose-rate (LDR) sources was measured for proof of principle and found to agree to within 3% of values obtained with other NIST traceable calibration techniques. The photon component of two 198Au radioactive stents was measured over a period of 3 days.

CONCLUSION

The air-kerma strength of HDR and LDR sources was measured for proof of principle and found to agree to within 3% of values obtained with other NIST traceable calibration techniques.

Late intravascular ultrasound findings of patients treated with brachytherapy for diffuse in-stent restenosis

This study aimed at evaluating long-term (24-month) effects of beta-irradiation (188Re-MAG3-filled balloon) using intravascular ultrasound (IVUS) in patients with in-stent restenosis (ISR). Long-term effects of beta-irradiation on intimal hyperplasia (IH) within the stented segment and vessel and lumen dimensions of nonstented adjacent segments in patients with ISR have not been sufficiently evaluated. Two-year follow-up IVUS was performed in 30 patients with patent ISR segments at 6-month follow-up angiography. Serial IVUS images were acquired at five equidistant intrastent sites and at three different reference segment sites. IH burden (%) was defined as 100 x (IH/stent area). Mean intrastent IH area and IH burden significantly increased between 6 and 24 months, from 2.1 +/- 1.1 to 2.6 +/- 1.4 mm2 (P < 0.001) and from 26% +/- 10% to 33% +/- 14% (P < 0.001), respectively. There was a significant decrease of mean external elastic membrane (from 10.1 +/- 3.9 to 9.7 +/- 3.9 mm2; P = 0.015) and lumen area (from 5.6 +/- 2.3 to 5.1 +/- 2.3 mm2; P = 0.021) within distal reference segments between 6 and 24 months. Target lesion revascularization (TLR) was performed in six patients (20%) between 6 and 24 months after beta-irradiation therapy. There were no significant differences between TLR and non-TLR groups except for a smaller minimum lumen area at 24 months in the TLR group. Because of a small amount of late loss between 6 and 24 months, most irradiated ISR vessel segments remained stable for up to 2 years. However, quantitative evidence of late catch-up was evident in most patients and was significantly associated with 24-month TLR in some patients.

Extra-stent vascular remodeling in in-stent restenosis after 188Re-MAG3 radiation therapy

BACKGROUND

The effect of beta-radiation on extra-stent vascular remodeling in patients with in-stent restenosis has not been studied. The correlation between the extent of extra-stent plaque proliferation and that of intimal hyperplasia (IH) in in-stent restenosis in patients who received beta-radiation therapy as well as conventional therapy has also not been studied.

METHODS

We evaluated the extra-stent remodeling in diffuse in-stent restenosis between a beta-radiation therapy patient group (188Re-MAG3, n=50) and a control group (n=9) by applying serial intravascular ultrasound (IVUS) analysis. Matching (post-intervention and follow-up) images were acquired at the follow-up lesion site and were available in 44 of 50 patients who received radiation therapy and in seven of nine control patients.

RESULTS

There was a significant increase of the external elastic membrane (EEM) area in both groups: 16.4 +/- 3.3 mm2 post-intervention to 17.1 +/- 3.3 mm2 at follow-up, P=0.001 in the radiation therapy group, and 16.8 +/- 4.0 mm2 post-intervention to 17.4 +/- 4.1 mm2 at follow-up, P=0.008 in the control group. There were no statistically significant differences of the Delta EEM area between the two groups: 0.7 +/- 0.4 mm2 in the radiation therapy group vs. 0.6 +/- 0.4 mm2 in the control group, P=0.389. The Delta IH area correlated with the Delta EEM area in the control group (r=0.826, P=0.022), but not in the radiation therapy group (r=0.016, P=0.919).

CONCLUSIONS

The findings of this IVUS study were that positive remodeling (increased EEM area) occurred equally in both control and irradiated patients with in-stent restenosis. The extent of remodeling was directly in proportion to IH in the control group, but no such relationship existed in the irradiated patient group.