Optimisation-based thermal treatment planning for catheter-based ultrasound hyperthermia

Abstract

A patient-specific optimisation-based hyperthermia treatment planning program for catheter-based ultrasound technology was developed for a priori evaluation of proposed applicator implant strategies and determination of initial applied power settings. The interstitial and endocavity heating applicators, designed for delivering 3-D controllable hyperthermia within High Dose Rate (HDR) brachytherapy implants, consist of linear and sectored arrays of ultrasound transducers with variable power control in both length and angle. A 3D biothermal model, which incorporates relevant anatomical structures and implant geometries based upon HDR treatment planning, has been developed to simulate the temperature distributions induced by these ultrasound applicators within the catheter implants. A temperature-based constrained optimisation algorithm was devised and integrated within the finite-element thermal solver to determine the optimal applied power levels. A temperature-expressed objective function and constraints were employed to limit maximum temperature (T(max)), maximise target coverage (T(target)), and minimise thermal exposure to normal tissue and surrounding organs. The optimisation-based treatment planning was applied on representative examples of clinical HDR implants for endocavity treatment of cervix (n = 3) and interstitial treatment of prostate (n = 3). Applicator positioning and orientation, T(max), and T(target), were varied, and temperature volume and thermal dose volume histograms calculated for each plan. The optimisation approach provided optimal applied power levels (4-24 independent transducer sections) leading to conforming or tailored temperature distributions for all cases, as indicated with improved temperature index T(90) in the target volume and negligible temperature and thermal dose (t(43,max) < 1 min) exposure in surrounding non-targeted tissues, such as bladder and rectum. The precision of the optimised power estimates was shown to be within <5% for a range of starting levels and were similarly convergent. The execution times of this optimisation (<16 min) and forward thermal treatment planning (<22 min) is sufficiently fast to be integrated into the clinical setting. This optimisation-based treatment planning platform for catheter-based ultrasound applicators is a useful tool to provide feedback for applicator selection (sector angle, number of transducer sections along length), positioning (angle or orientation), optimal initial power settings, and has potential to significantly improve the delivery of hyperthermia in conjunction with HDR brachytherapy.

Multiple applicator hepatic ablation with interstitial ultrasound devices: Theoretical and experimental investigation

“…Based on the positions of implanted applicators as determined by imaging, forward and/or inverse treatment planning tools may be used to determine appropriate power levels for adequate thermal coverage of the target, as has been implemented for interstitial ultrasound hyperthermia procedures. 69 CT and ultrasound are the most commonly used imaging modalities for guiding percutaneous tumor ablation. 70 For parallel implants, the use of surface templates (as used for currently available RF and MW ablation systems) can augment imaging data to assess applicator positioning.…”

Utility of treatment planning for thermochemotherapy treatment of nonmuscle invasive bladder carcinoma

“…1,5,8 Treatment planning based on both specific absorption rate (SAR) and temperature-based optimization has been used to provide better targeted heating in various sites. [9][10][11] Treatment planning that enhances the ability to focus heat at the bladder has also been reported. For example, van Dijk et al 12 showed increased bladder SAR using treatment planning to optimize the SAR distribution in a selected two-dimensional plane.…”

Continuum Models for the Cooling Effect of Blood Flow on Thermal Ablation Techniques

“…Since, on the first steps of cryoablation, an open surgery was required due to large probe sizes and the risk of bleeding, RF ablation has gained wide acceptance as a minimally invasive technique and becomes the most widely used hyperthermia technique to treat liver cancer, see [2][3][4] and the references therein. Nowadays the cryogenic treatment has modern catheters that can be 2 mm maximum diameter with 90 cm flexible length and then it also belongs to the more recent area of study of the thermal therapies as well as the application of imaging, ultrasound, and laser modalities among others [5][6][7][8][9]. Although our data may be specific to RF ablation in the liver, the continuum models are probably valid for all thermal ablation energy sources and for other organs which are close to vessels.…”