Temperature superposition for fast computation of 3D temperature distributions during optimization and planning of interstitial ultrasound hyperthermia treatments

Abstract

Purpose A temperature superposition method has been developed for fast optimization and planning of interstitial hyperthermia treatments with convectively-cooled multi-transducer ultrasound applicators integrated within HDR brachytherapy catheters. Methods Steady-state temperature distributions produced by individual tubular transducers capable of directional heating were pre-computed using FEM methods. The composite temperature distributions generated by multi-applicator implants were approximated as superposition sums of the pre-computed temperature profiles. Composite temperature distributions produced by the multi-applicator implants were also computed using accurate but computationally expensive FEM methods (considered here as the validation standard). Both methods were used for temperature calculation on a range of test implant geometries and representative patient cases [HDR implants in prostate (n = 13) and cervix (n = 2)], with optimized treatment plans created for the latter. Results Difference between temperatures calculated by the superposition and FEM methods was below 0.37 °C (95% confidence) in test implants at clinically relevant acoustic intensities (0.3 – 2.0 W/cm2) and blood perfusion (2 kg/m3/s). Difference in 41 °C isothermal volumes was below 8.3%. Superposition based optimizations followed by FEM forward calculations (hybrid plans) were completed 4 – 7 times faster than FEM-only plans (FEM optimization + FEM forward). Mean T90, T50 and T10 values from both plans were within 0.3 °C, 0.4 °C and 0.45 °C respectively, and the mean acoustic intensities were within 0.23 W/cm2. Conclusions Temperature superposition provides a fast technique for forward or optimized planning of interstitial ultrasound hyperthermia treatments with calculations comparable to more accurate but time consuming FEM methods.

Clinical integration of software tool VEDO for adaptive and quantitative application of phased array hyperthermia in the head and neck

“…Inter-patient variation of EM and thermal properties exists and could be a source of error. Online MRI-based temperature mapping during HT -as done in [30] for intravenous ultrasound HT, in [17,[31][32][33] for phased array HT, and in [34] for high-intensity focused ultrasound (in rats) -should be used to validate the complete patient and HYPERcollar set-up. Secondly, the correlation between the current goal function, HTQ and temperature should still be proven for H&N HT.…”

Catheter-based ultrasound technology for image-guided thermal therapy: Current technology and applications

“…Similar CBUS tubular applicators were used in a clinical pilot study to deliver hyperthermia in conjunction with HDR brachytherapy for advanced prostate and cervical cancer [38]. Also, studies related to hyperthermia treatment schema [38, 39] and optimization with CBUS tubular applicators have been reported [40, 41]. Another potential application is the treatment of large uterine fibroids.…”

“…CT images of brachytherapy implants are also used to plan interstitial CBUS hyperthermia applied through the implanted catheters [38, 40, 41]. Electromagnetic tracking methods have been integrated with cone-beam CT for guiding needle placement for interstitial ultrasound ablation [105].…”

Modelling of endoluminal and interstitial ultrasound hyperthermia and thermal ablation: Applications for device design, feedback control and treatment planning

“…Ultimately, thermometry available from in vivo clinical data can be used to validate theoretical models. As an example, temperature measurements obtained during a pilot study of interstitial ultrasound hyperthermia in prostate [108] were compared to 3D temperature profiles estimated using FEM-based patient-specific models [26, 47]. For these treatments, the measured and simulated T50 values in the hyperthermia target volume were in good agreement ranging between 40.1 – 43.9 °C and 40.3 – 44.9 °C, respectively, and transient changes in temperature correlated consistently between measurement and simulation (Figure 3).…”

“…[47] developed a temperature superposition technique for rapidly computing the temperature profile induced by catheter-based ultrasound applicators. This method used precomputed solutions of the temperature profile induced by an individual ultrasound transducer, to estimate the temperature profile induced by an array of applicators employing multiple transducers.…”