Comparison of temperature distributions in interstitial hyperthermia: experiments in bovine tongues versus generic simulations

Raaymakers, B W; Crezee, J.; Lagendijk, J.J.W.

doi:10.1088/0031-9155/43/5/011

Cited by 22 publications

(15 citation statements)

References 23 publications

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“…(16,22,23). Furthermore, similar predictions to those reported here are described by Nelson and Nunnenly (24) who used a hemispherical tissue layered numerical model of the human head/brain.…”

supporting

confidence: 85%

Numerical Modeling of Temperature Distributions within the Neonatal Head

Hand²,

et al. 2000

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Introduction of hypothermia therapy as a neuroprotection therapy after hypoxia-ischemia in newborn infants requires appraisal of cooling methods. In this numerical study thermal simulations were performed to test the hypothesis that cooling of the surface of the cranium by the application of a cooling bonnet significantly reduces deep brain temperature and produces a temperature differential between the deep brain and the body core. A realistic threedimensional (3-D) computer model of infant head anatomy was used, derived from magnetic resonance data from a newborn infant. Temperature distributions were calculated using the Pennes heatsink model. The cooling bonnet was at a constant temperature of 10°C. When modeling head cooling only, a constant body core temperature of 37°C was imposed. The computed result showed no significant cooling of the deep brain regions, only the very superficial regions of the brain are cooled to temperatures of 33-34°C. Poor

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confidence: 85%

Numerical Modeling of Temperature Distributions within the Neonatal Head

Hand²,

et al. 2000

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“…Models that determine the temperature distribution are available, but for accurate calculated detailed knowledge of the thermal tissue properties and tissue perfusion are required. Techniques for measuring this thermal data input are currently under development and are used to verify the thermal models 11 . However, these techniques are not commonly available.…”

Section: Introductionmentioning

confidence: 99%

A flexible optimization tool for hyperthermia treatments with RF phased array systems

Wiersma

Maarseveen

Dijk

2002

International Journal of Hyperthermia

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In hyperthermia treatments performed with a radio-frequency phased array, the main issue to apply the excitation amplitudes and phases of the applicators for which tumour heating is optimal, i.e. the maximal therapeutic gain without unwanted side effects. Due to the complex interaction of the radiated EM-field and the patient's tissues, it is very difficult to find these optimal excitation (amplitude and phase) parameters by intuition. Calculation of the EM-field distribution within the patient can aid in finding the optimal excitation setting. However, this remains a difficult task because of the degrees of freedom available (2n - 1, with n the number of applicators in the array) and because a large temperature elevation may occur at healthy tissue sites resulting in unwanted side effects, e.g. pain or healthy tissue damage. Therefore, determining the excitation amplitudes and phases yielding optimal tumour heating can be done effectively only by application of a computerized optimization procedure. Optimization of the temperature distribution in the patient requires detailed knowledge of the thermal tissue parameters. Techniques for determining these properties are not commonly available and the use of averaged values for parameters like the tissue perfusion is expected to introduce large errors for individual patient treatment planning. As a consequence, the SAR distribution, being proportional to the temperature increase at treatment start, is more often selected for optimization. The 'optimized' excitation amplitudes and phases are found by maximization of a certain SAR ratio. Several propositions for this SAR ratio have been reported in the literature, e.g. the ratio of the SAR at the tumour site and the SAR at sites where unwanted side effects may occur. However, the definition of these ratios does not constrain the SAR value at these tissue locations to a safe value. In this paper, a tool for the optimization of the SAR distribution including the specification of constraints is presented. The tool focuses on the definition of the average SAR as a function of the excitation amplitudes and phases in a volume of arbitrary size (e.g. the tumour volume or the whole patient volume). These functions can be applied in either customized or commercially available optimization routines and they enable the definition of constraints for the average SAR in a certain volume. The described tool is illustrated for a patient case, showing the flexibility and easy application of the tool.

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“…The thermal simulations are based on the geometry G MR , superimposed with the tracked vasculature, the two comprising the computational domain for the DIVA program. DIVA was verified both theoretically, by Van Leeuwen et al 26,27 and experimentally, by Raaymakers et al 28,29 DIVA models the heat transfer in perfused tissue. The thermal impact of each discrete vessel is taken into account individually.…”

Section: Thermal Simulations With Divamentioning

confidence: 90%

Discretizing large traceable vessels and using DE‐MRI perfusion maps yields numerical temperature contours that match the MR noninvasive measurements

et al. 2001

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The success of hyperthermia treatments is dependent on thermal dose distribution. However, the three-dimensional temperature distribution remains largely unknown. Without this knowledge, the relationship between thermal dose and outcome is noisy, and therapy cannot be optimized. Accurate computations of thermal distribution can contribute to an optimized therapy. The hyperthermia modeling group in the Department of Radiotherapy, University Medical Center Utrecht devised a Discrete Vasculature [Kotte et al., Phys. Med. Biol. 41, 865-884 (1996)] model that accounts for the presence of vessel trees in the computational domain. The vessel tree geometry is tracked using magnetic resonance (MR) angiograms to a minimum diameter between 0.6 and 1 mm. However, smaller vessels (0.2-0.6 mm) are known to account for significant heat transfer. The hyperthermia group at Duke University Medical Center has proposed using perfusion maps derived from dynamic-enhanced magnetic resonance imaging to account for the tissue perfusion heterogeneity [Craciunescu et al., Int. J. Hyperthermia 17, 221-239 (2001)]. In addition, techniques for noninvasive temperature measurements have been devised to measure temperatures in vivo [Samulski et al., Int. J. Hypertherminal, 819-829 (1992)]. In this work, a patient with high-grade sarcoma has been retrospectively modeled to determine the temperature distribution achieved during a hyperthermia treatment. Available for this model were MR depicted geometry, angiograms, perfusion maps, as necessary for accurate thermal modeling, as well as MR thermometry data for validation purposes. The vasculature assembly through modifiable potential program [Van Leeuwen et al., IEEE Trans. Biomed. Eng. 45, 596-604 (1998)] was used in order to incorporate the traceable large vessels. Temperature simulations were made using different approaches to describe perfusion. The simulated cases were the bioheat equation with constant perfusion rates per tissue type, perfusion maps alone, tracked vessel tree and perfusion maps, and generated vessel tree. The results were compared with MR thermometry data for a single patient data set, concluding that a combination between large traceable vessels and perfusion map yields the best results for this particular patient. The technique has to be repeated on several patients, first with the same type of malignancy, and after that, on patients having malignancies at other different sites.

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Comparison of temperature distributions in interstitial hyperthermia: experiments in bovine tongues versus generic simulations

Cited by 22 publications

References 23 publications

Numerical Modeling of Temperature Distributions within the Neonatal Head

Numerical Modeling of Temperature Distributions within the Neonatal Head

A flexible optimization tool for hyperthermia treatments with RF phased array systems

Discretizing large traceable vessels and using DE‐MRI perfusion maps yields numerical temperature contours that match the MR noninvasive measurements

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