Theoretical comparison of intraluminal heating techniques

Abstract

Introduction: This study compared simulated temperature distributions of intraluminal heating devices, concerning penetration and homogeneity. A hot water balloon, a 434-MHz monopole and a 915-MHz dipole antenna, both with incorporated cooling, and a 27-MHz applicator were investigated. Methods: The hot water balloon had an inlet temperature of 45°C and a flow rate of 7.85 ml s-1. The cooling water and air had a temperature of 41°C and 37°C and a flow rate of 5.89 ml s-1 and 1.8 l s-1, respectively. A 27-MHz applicator consisting of one or two electrode(s) was modelled to demonstrate axial steering for inhomogeneous tissue properties. Calculated power distributions were scaled to a total power of 10 W in tissue before the corresponding temperature distributions were calculated. Results: The hot water balloon and the 27-MHz device showed a thermal penetration depth of ∼4 and ∼10 mm, respectively. The penetration depths of the 434- and 915-MHz applicators were comparable: ∼10 and ∼16 mm with water and air cooling, respectively. With the 27-MHz applicator, spatial steering was applied to minimize temperature gradients along the applicator. The 434- and 915-MHz antennas have no steering possibilities. The temperature distribution of the hot water balloon is not affected by inhomogeneous dielectric properties, only slightly by inhomogeneous perfusion. Conclusion: A hot water balloon is useful for heating tumours with a limited infiltration in tissue, while a 27-MHz device has the best potential to realize a homogeneous temperature distribution in larger tumours.