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

摘要

Purpose: A temperature superposition method has been developed for fast optimisation and planning of interstitial hyperthermia treatments with convectively cooled multi-transducer ultrasound applicators integrated within high dose rate (HDR) brachytherapy catheters. Methods: Steady-state temperature distributions produced by individual tubular transducers capable of directional heating were pre-computed using finite element models (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 optimised treatment plans created for the latter. Results: Difference between temperatures calculated by the superposition and FEM methods was below 0.37°C (95% confidence interval) in test implants at clinically relevant acoustic intensities (0.3–2.0?W/cmsup2/sup) and blood perfusion (2?kg/msup3/sup/s). Difference in 41°C isothermal volumes was below 8.3%. Superposition-based optimisations followed by FEM forward calculations (hybrid plans) were completed 4–7 times faster than FEM-only plans (FEM optimisation?+?FEM forward). Mean Tsub90/sub, Tsub50/sub and Tsub10/sub 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/cmsup2/sup. Conclusions: Temperature superposition provides a fast technique for forward or optimised planning of interstitial ultrasound hyperthermia treatments with calculations comparable to more accurate but time consuming FEM methods.