The future of coronary artery radiation therapy—“the CART before the (unbridled) horse!”

Intravascular brachytherapy using 90Sr for saphenous vein grafts having diameters ranging from 2.0–5.0 mm

PURPOSE

Symptomatic coronary artery disease is routinely treated with angioplasty and stenting. Unfortunately, treatment failure in the form of in-stent restenosis (ISR) occurs relatively frequently. Intravascular brachytherapy (IVBT) is a safe and effective method proven to markedly reduce the rate of ISR in native coronary arteries. The commercially available devices for IVBT are not FDA-approved for treatment of saphenous vein grafts (SVG). This article presents calculated dosimetry for treatment of a wide range of SVG, in addition to further evaluating the dose homogeneity for native coronary arteries.

METHODS AND MATERIALS

AAPM Task Group 43 and 60 formalisms permitted dose calculations for a wide range of vessel internal diameters (phi) in both native coronary arteries and SVG. Doses were analytically calculated for the Novoste Beta-Cath 5.0 French (F) treatment devices (30, 40, and 60 mm sourcetrains) when employed for the treatment of native vessels with 2.7 <or= phi <or= 4.0 mm and for SVG with 2.0 <or= phi <or= 5.0 mm. This latter range of phi was segmented into 7 bins to facilitate rapid clinical implementation with minimal errors. Calculations of dose and dose rate for the 3.5 F devices were also performed. Dose inhomogeneity in the form of dose maxima and minima were calculated for the 3.5 and 5.0 F catheters, with the 30, 40, and 60 mm sourcetrains, and for 2.0 <or= phi <or= 5.0 mm.

RESULTS

The calculated doses rates for the 30 mm device were in agreement (typically +/- 0.3%) with measured dose rates. Reference dose calculations performed for SVG with 2.0 <or= phi <or= 5.0 mm were in alignment with those used for the more narrow range of native coronary arteries currently approved for IVBT. Errors associated with using a phi binning technique for simplifying clinical implementation did not exceed 15%, and were typically under 9%. The degree of dose inhomogeneity at a depth of 0.5 mm increased as phi increased, catheter size decreased, and sourcetrain length decreased, and was -42% and +101% relative to the prescribed dose for the 40 mm 5.0 F system with phi = 4.0 mm.

CONCLUSIONS

Use of 7 phi bins facilitates rapid clinical implementation of IVBT in the typical cardiac catheterization laboratory. While calculation of reference dose for treatment of large vessels is possible with established formalisms, the degree of dose inhomogeneity in light of current clinical results suggests further research is needed.