On estimation of the temperature maximum in intraluminal or intracavitary hyperthermia

Abstract

During intraluminal or intracavitary hyperthermia treatments, limited non-invasive temperature information is available, which may result in sub-optimal treatment control. This article describes a method for estimating temperature maximums and their corresponding locations in tissue heated by a cylindrical applicator with an incorporated cooling system, assuming a hollow cylinder of homogeneous tissue. The main purpose of this study is intraluminal heating of tumours at the oesophagus, but the principle described is generally applicable for cylindrical applicators. When assuming no perfusion and only radial heat flow in the heated tissue, an analytical expression for the temperature profile can be derived such that the complete profile can be reconstructed from the inner wall temperature only. For situations with perfusion, finite difference simulations have been performed and the resulting simulated inner wall temperature was put into the analytical expression to obtain an estimation for the maximum temperature and the corresponding location. This way, an estimation method was developed which does not require a priori knowledge of the perfusion rate or invasive thermometry. For volumetric perfusion rates in the clinically relevant range of 0-10 kg m-3 s-1, the deviations between simulated and estimated temperature maximums were less than 10% and the difference in location was typically a few tenths of a millimetre. These deviations are small enough for treatment control purposes.

Hyperthermia Treatment Planning Including Convective Flow in Cerebrospinal Fluid for Brain Tumour Hyperthermia Treatment Using a Novel Dedicated Paediatric Brain Applicator

“…The section outside the treatment volume, i.e., the part of the head below the tumour that is not covered by the applicator, was modelled as muscle. The tissue parameters used in the simulations are based on literature values and are listed in Table 1 [50,51,52,53]. Normothermal perfusion coefficients were used, except for muscle, for which a four-fold increased hyperthermic perfusion rate of 3.6 kg/(m 3 s) was used reflecting the enhanced muscle perfusion levels in response to hyperthermic temperature elevations [53].…”

“…The tissue parameters used in the simulations are based on literature values and are listed in Table 1 [50,51,52,53]. Normothermal perfusion coefficients were used, except for muscle, for which a four-fold increased hyperthermic perfusion rate of 3.6 kg/(m 3 s) was used reflecting the enhanced muscle perfusion levels in response to hyperthermic temperature elevations [53]. As in practice, hyperthermia treatments for medulloblastoma patients would most likely be delivered post-operatively, we also created a ‘post-operative mesh’, in which the tumour has been excised and the region was filled with CSF.…”

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

“…These planning frameworks may utilize numerical modeling to simulate 3D temperature distributions. Finite element models (FEM) [4] or finite difference (FDTD) [5] methods have been employed to compute position dependent specific absorption rates (SAR), based on the type of treatment energy modality, and the concomitant temperature profiles. Following SAR computations, the temperature calculations may include relatively simple bio-heat transfer equation solution assuming homogenous blood perfusion [6] or more involved approaches which account for physiological perfusion changes [7] or discrete vasculature models [8].…”

Tilted Fiber Bragg Grating Active Heater for Controlled and Localised Hyperthermia

“…Although various theoretical methods have been proposed and used to estimate the temperature distribution around the applicator, they are not very reliable in clinical applications, and hence the need for real-time monitoring arises [87].…”

“…Three major configurations, interferometric sensors, distributed sensors, and gratingbased sensors represent the fiber optic sensors (FOS) field [83,85,87,[131][132]140].…”