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J Crezee

Publications and source records attributed to J Crezee.

At least 19 recordsLinked to original sources
PubMed2006

Prospective treatment planning to improve locoregional hyperthermia for oesophageal cancer.

BACKGROUND: In the Academic Medical Center (AMC) Amsterdam, locoregional hyperthermia for oesophageal tumours is applied using the 70 MHz AMC-4 phased array system. Due to the occurrence of treatment-limiting hot spots in normal tissue and systemic stress at high power, the thermal dose achieved in the tumour can be sub-optimal. The large number of degrees of freedom of the heating device, i.e. the amplitudes and phases of the antennae, makes it difficult to avoid treatment-limiting hot spots by intuitive amplitude/phase steering. AIM: Prospective hyperthermia treatment planning combined with high resolution temperature-based optimization was applied to improve hyperthermia treatment of patients with oesophageal cancer. METHODS: All hyperthermia treatments were performed with 'standard' clinical settings. Temperatures were measured systemically, at the location of the tumour and near the spinal cord, which is an organ at risk. For 16 patients numerically optimized settings were obtained from treatment planning with temperature-based optimization. Steady state tumour temperatures were maximized, subject to constraints to normal tissue temperatures. At the start of 48 hyperthermia treatments in these 16 patients temperature rise (DeltaT) measurements were performed by applying a short power pulse with the numerically optimized amplitude/phase settings, with the clinical settings and with mixed settings, i.e. numerically optimized amplitudes combined with clinical phases. The heating efficiency of the three settings was determined by the measured DeltaT values and the DeltaT-ratio between the DeltaT in the tumour (DeltaToes) and near the spinal cord (DeltaTcord). For a single patient the steady state temperature distribution was computed retrospectively for all three settings, since the temperature distributions may be quite different. To illustrate that the choice of the optimization strategy is decisive for the obtained settings, a numerical optimization on DeltaT-ratio was performed for this patient and the steady state temperature distribution for the obtained settings was computed. RESULTS: A higher DeltaToes was measured with the mixed settings compared to the calculated and clinical settings; DeltaTcord was higher with the mixed settings compared to the clinical settings. The DeltaT-ratio was approximately 1.5 for all three settings. These results indicate that the most effective tumour heating can be achieved with the mixed settings. DeltaT is proportional to the Specific Absorption Rate (SAR) and a higher SAR results in a higher steady state temperature, which implies that mixed settings are likely to provide the most effective heating at steady state as well. The steady state temperature distributions for the clinical and mixed settings, computed for the single patient, showed some locations where temperatures exceeded the normal tissue constraints used in the optimization. This demonstrates that the numerical optimization did not prescribe the mixed settings, because it had to comply with the constraints set to the normal tissue temperatures. However, the predicted hot spots are not necessarily clinically relevant. Numerical optimization on DeltaT-ratio for this patient yielded a very high DeltaT-ratio ( approximately 380), albeit at the cost of excessive heating of normal tissue and lower steady state tumour temperatures compared to the conventional optimization. CONCLUSION: Treatment planning can be valuable to improve hyperthermia treatments. A thorough discussion on clinically relevant objectives and constraints is essential.

Adenocarcinoma↗
PubMed2006

Reliability of temperature and SAR measurements at oesophageal tumour locations.

INTRODUCTION: For treatment of oesophageal cancer, neo-adjuvant locoregional hyperthermia (HT) has been applied in combination with chemotherapy (ChT) +/- radiotherapy (RT) at the institute. Until now, 26 patients were treated within a completed phase I study combining HT with ChT and 29 patients within an ongoing phase II study combining HT with ChT + RT. METHODS: HT was given with the 70 MHz AMC-4 waveguide system. Initially, oesophageal temperatures were measured using multi-sensor thermocouple probes (TCs) inside a nasogastric tube (NT), but the question arose whether these measurements were reliable enough to quantify the achieved tumour temperatures accurately. Presently, TCs are mounted on the outside of an inflatable balloon catheter (BC) for better intra-luminal fixation and better contact with the tumour. During 14 treatment sessions in four patients TCs inside a NT and mounted on a BC were used simultaneously. Data from these 14 treatment sessions were used to compare temperature and Specific Absorption Rate (SAR) measurements ('DeltaT-measurements') using NTs or BCs. To determine the predictive value of the local SAR for the tumour temperatures achieved during treatment, the relation between the initial DeltaT and steady state temperature (SST) was evaluated. RESULTS: There was a strong correlation between the temperature measured in the NT (Ttube) and the temperature measured with a BC (Tballoon): R = 0.88 +/- 0.13. However, Ttube was on average approximately 1 degrees C higher than Tballoon and there was a large variation between the different treatments in the relation between both measurements, rendering Ttube a probably unreliable measure for tumour temperatures. The correlation between the DeltaT measured in the NT (DeltaTtube) and with a BC (DeltaTballoon) was rather weak: R = 0.46 +/- 0.25. The correlation between the initial DeltaT and the SST was much stronger for the BC measurements, R = 0.78 +/- 0.19, than for the NT measurements, R = 0.61 +/- 0.23. Thus, DeltaTballoon has a higher predictive value for the achieved tumour temperatures than DeltaTtube. Both DeltaT and SST were generally higher for the NT measurements than for the BC measurements, suggesting an over-estimation of tumour temperatures. Averaged over all treatments in the phase I trial using a NT (20 treatments) or a BC (45 treatments), T90 was significantly higher when measured with a NT. CONCLUSION: Oesophageal temperature and SAR (DeltaT) measurements inside a NT are less reliable than BC measurements. These artefacts are due to bad thermal contact with the tumour tissue and are, therefore, not specific for thermocouple thermometry. For reliable temperature or SAR measurements inside lumina or cavities good thermal contact must be assured, e.g. by using a balloon catheter.

Brachytherapy↗
PubMed2005

High-resolution temperature-based optimization for hyperthermia treatment planning.

In regional hyperthermia, optimization techniques are valuable in order to obtain amplitude/phase settings for the applicators to achieve maximal tumour heating without toxicity to normal tissue. We implemented a temperature-based optimization technique and maximized tumour temperature with constraints on normal tissue temperature to prevent hot spots. E-field distributions are the primary input for the optimization method. Due to computer limitations we are restricted to a resolution of 1 x 1 x 1 cm3 for E-field calculations, too low for reliable treatment planning. A major problem is the fact that hot spots at low-resolution (LR) do not always correspond to hot spots at high-resolution (HR), and vice versa. Thus, HR temperature-based optimization is necessary for adequate treatment planning and satisfactory results cannot be obtained with LR strategies. To obtain HR power density (PD) distributions from LR E-field calculations, a quasi-static zooming technique has been developed earlier at the UMC Utrecht. However, quasi-static zooming does not preserve phase information and therefore it does not provide the HR E-field information required for direct HR optimization. We combined quasi-static zooming with the optimization method to obtain a millimetre resolution temperature-based optimization strategy. First we performed a LR (1 cm) optimization and used the obtained settings to calculate the HR (2 mm) PD and corresponding HR temperature distribution. Next, we performed a HR optimization using an estimation of the new HR temperature distribution based on previous calculations. This estimation is based on the assumption that the HR and LR temperature distributions, though strongly different, respond in a similar way to amplitude/phase steering. To verify the newly obtained settings, we calculate the corresponding HR temperature distribution. This method was applied to several clinical situations and found to work very well. Deviations of this estimation method for the AMC-4 system were typically smaller than 0.2 degrees C in the volume of interest, which is accurate enough for treatment planning purposes.

Body Burden↗
PubMed2005

On estimation of the temperature maximum in intraluminal or intracavitary hyperthermia.

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.

Humans↗
PubMed2001

Determination and validation of the actual 3D temperature distribution during interstitial hyperthermia of prostate carcinoma.

To determine the thermal dose of a hyperthermia treatment, knowledge of the three-dimensional (3D) temperature distribution is mandatory. The aim of this paper is to validate an interstitial hyperthermia treatment planning system with which the full 3D temperature distribution can be obtained in individual patients. Within a phase I study, 12 patients with prostate cancer were treated with interstitial hyperthermia using our multi electrode current source interstitial hyperthermia treatment (MECS IHT) system. The temperature distribution was measured from within the heating devices and by additional thermometry. The perfusion level was estimated and the heating implant reconstructed. The steady-state temperature distribution was calculated using our interstitial hyperthermia treatment planning system. The simulated temperature distribution was validated by individually comparing the measured and simulated thermo-sensors, both for the thermometry integrated with the heating applicators and the additional thermometry. The entire procedure was also performed on a no-flow agar-agar phantom. It was shown that the calculated temperature distribution of an individual patient during MECS interstitial hyperthermia is very heterogeneous. The validation indicates that the calculated temperature elevations match the measurements within approximately 1 degrees C. Possible improvements are more precise reconstruction, incorporation of discrete vasculature and using a temperature-dependent, heterogeneous perfusion distribution. Further technical improvements of the MECS-IHT system may also result in better temperature calculations.

Agar↗
PubMed2000

Modelling individual temperature profiles from an isolated perfused bovine tongue.

To predict the temperature distribution during hyperthermia treatments a thermal model that accounts for the thermal effect of blood flow is mandatory. The DIscrete VAsculature (DIVA) thermal model developed at our department is able to do so; geometrically described vessels are handled individually and the remaining vasculature is modelled collectively. The goal of this paper is to experimentally validate the DIVA model by comparing measured with modelled temperature profiles on an individual basis. Temperature profiles in an isolated bovine tongue heated with three hot water tubes were measured at three controlled perfusion levels, 0, 6 and 24 ml (100 g)(-1) min(-1). The geometries of the tongue, the hot water tubes, thermocouples and discrete vasculature down to 0.5 mm diameter were reconstructed by using cryo-microtome slices at 0.1 mm cubic resolution. This reconstruction of the experimental set-up is used for the modelling of individual profiles. In a no-flow agar-agar phantom, DIVA showed nearly perfect correspondence between measurements and simulations. In the isolated bovine tongue the correspondence at no flow was slightly disturbed due to geometrical distortion in the reconstruction of the experimental set-up. Measurements showed decreasing temperature profiles with increasing perfusion. DIVA correctly predicted this decrease in temperature as well as the thermal impact of a large vessel close to a thermocouple. Blood flow was modelled using discrete vasculature and using a heat sink model. Although at 24 ml (100 g)(-1) min(-1) correspondence between heat sink simulations and measurements was reasonable, modelling discrete vasculature yielded the best correspondence at both 6 and 24 ml (100 g)(-1) min(-1). The results strongly suggest that with accurate data acquisition DIVA can predict temperature profiles on an individual basis. For this kind of patient-specific treatment planning in the clinic, geometrical reconstruction of the anatomy, vasculature and the heating implant is necessary. MRI is capable of providing these data. Further research will be done on thermal simulations of actual clinical hyperthermia treatments.

Agar↗
PubMed1998

Thermal properties of capacitively coupled electrodes in interstitial hyperthermia.

The multi-electrode current source (MECS) interstitial hyperthermia system which is used for treatment of cancer, employs segmented electrodes inserted in plastic tubes implanted in the treatment volume. The mean power deposition of the individual electrodes is controlled by varying the duty cycle of the RF signal applied to the electrodes, using thermocouples inside the electrodes for thermometry. A non-zero loss angle results in self-heating of the catheter. The thermal influence of self-heating was investigated and an analysis of the measurement of temperatures inside the catheter during and after heating is presented. Analytical models and a high-resolution numerical model were used for the calculation of steady state and transient distributions, respectively. The model results are compared with experimental data obtained in a muscle equivalent phantom. Results indicate that there is no difference between temperature inside and outside the catheter when using lossless catheter materials (e.g. PE and PTFE). Self-heating in the catheter wall has an adverse effect on the uniformity of the stationary temperature distribution and the reliability of temperature measurement with internal thermometry. These problems remain within acceptable limits for mildly lossy materials; the difference between the temperature inside and outside is only 6% when using low-loss Nylon. Analysis of the thermal decay after power-off shows that low-loss materials allow more time to obtain an accurate estimate of the tissue temperature at the catheter wall during power-on. This effect is enhanced by the presence of minute air layers in the applicator. Distortion of temperature gradients along the catheter was also investigated. Key factors are the thermal conduction across the catheter wall, and especially the presence of minute layers of air between consecutive layers of the probe. The distortion extends less than two millimetres, which is acceptable. The simulation results are compatible with measurements in phantoms and show that, if the proper choice of materials is made, the MECS applicator answers our expectations and that the temperature measurement inside the catheter can be used for direct feedback treatment control.

Biophysical Phenomena↗
PubMed1998

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

Temperature distributions resulting from hyperthermia treatments on isolated perfused bovine tongues were compared with simulations by a treatment planning system. The aim was to test whether the discrete vessel model used for the treatment planning is able to predict correct generic temperature distributions. Tongues were heated with the multielectrode current source interstitial hyperthermia treatment (MECS IHT) system, while the steady-state temperature distribution was mapped by scanning 10 thermocouples along paths perpendicular to the interstitial implant. For simulations a tongue was defined with generic discrete vasculature and an electrode implant analogue to the experiments. To model vascular generations not described discretely, a local heatsink was implemented at the end of each terminating branch. The discretely modelled vasculature showed itself on the temperature distributions in two ways. Individual vessels caused very local, sharp wells in the tracked temperature profiles. In the presence of large vessels a collective behaviour was also seen, i.e. a regional lowering of temperature. Both phenomena can be recognized in the experimentally obtained temperature distributions too. Predicting correct generic temperature distributions is feasible with the discrete vessel model used.

Animals↗
PubMed1997

Implications of using thermocouple thermometry in 27 MHz capacitively coupled interstitial hyperthermia.

The 27 MHz Multi Electrode Current Source (MECS) interstitial hyperthermia system uses segmented electrodes, 10-20 mm long, to steer the 3D power deposition. This power control at a scale of 1-2 cm requires detailed and accurate temperature feedback data. To this end seven-point thermocouples are integrated into the probes. The aim of this work was to evaluate the feasibility and reliability of integrated thermometry in the 27 MHz MECS system, with special attention to the interference between electrode and thermometry and its effect on system performance. We investigated the impact of a seven-sensor thermocouple probe (outer diameter 150 microns) on the apparent impedance and power output of a 20 mm dual electrode (O.D. 1.5 mm) in a polyethylene catheter in a muscle equivalent medium (sigma 1 = 0.6 S m-1). The cross coupling between electrode and thermocouple was found to be small (1-2 pF) and to cause no problems in the dual-electrode mode, and only minimal problems in the single-electrode mode. Power loss into the thermometry system can be prevented using simple filters. The temperature readings are reliable and representative of the actual tissue temperature around the electrode. Self-heating effects, occurring in some catheter materials, are eliminated by sampling the temperature after a short power-off interval. We conclude that integrated thermocouple thermometry is compatible with 27 MHz capacitively coupled interstitial hyperthermia. The performance of the system is not affected and the temperatures measured are a reliable indication of the maximum tissue temperatures.

Electrodes↗
PubMed1997

Design of applicators for a 27 MHz multielectrode current source interstitial hyperthermia system; impedance matching and effective power.

In interstitial heating one of the main requirements for achieving a certain elevated temperature in a tumour is that the effective power per applicator (Peff), i.e. the power which is actually deposited in the tissue, is sufficiently high. In this paper this requirement is discussed for the applicators of the 27 MHz multielectrode current source (MECS) interstitial hyperthermia (IHT) system. To minimize power reflection, the applicator impedance was matched with the generator impedance by adjusting the length of the coaxial cable in between. Transmission line losses, applicator efficiency and subsequently Peff were computed for several applicator types. The actual Peff per electrode was obtained from calorimetric measurements. Experiments with RC loads, which can be seen as perfect applicators, were performed to investigate the effect of mismatching on Peff. Applicator losses were measured for clinically used applicators, both single- and dual-electrode, utilizing saline phantoms. A simple spherical tumour model, using the effective heat conductivity (keff) to account for heat transport, was used to estimate Peff for a given tumour size, implant size and applicator density. Computations of Peff of various MECS-IHT electrodes were in close agreement with the phantom measurements. Most of the initial generator power was absorbed in the transmission line (60-65%). The efficiency of the applicators was about 65%. For both single- and dual-electrode applicators the effective electrode power was found to be about 1 W. Model calculations show that Peff of 1 W is sufficient to reach a minimum tumour temperature of 43 degrees C in well perfused tumours (keff = 3 W m-1 degree C-1), using a typical implant with 2 cm electrodes and 1.5 cm spacing. Mismatching can considerably affect Peff. Both a reduction to almost zero and a two-fold increase are possible. However, because the matching theory is well understood, mismatching is not a serious problem in clinical practice and can even be used to increase Peff if necessary. We conclude that the applicator design and the impedance matching method chosen in the MECS system allow heating to temperatures in the therapeutic range with implants used in clinical practice.

Biophysical Phenomena↗
PubMed1997

Accuracy of geometrical modelling of heat transfer from tissue to blood vessels.

We have developed a thermal model in which blood vessels are described as geometrical objects, 3D curves with associated diameters. Here the behaviour of the model is examined for low resolutions compared with the vessel diameter and for strongly curved vessels. The tests include a single straight vessel and vessels describing the path of a helix embedded in square tissue blocks. The tests show the excellent behaviour of our discrete vessel implementation.

Blood Vessels↗
PubMed1997

Tests of the geometrical description of blood vessels in a thermal model using counter-current geometries.

We have developed a thermal model, for use in hyperthermia treatment planning, in which blood vessels are described as geometrical objects; 3D curves with associated diameters. For the calculation of the heat exchange with the tissue an analytic result is used. To arrive at this result some assumptions were made. One of these assumptions is a cylindrically symmetric temperature distribution. In this paper the behaviour of the model is examined for counter-current vessel geometries for which this assumption is not valid. Counter-current vessel pairs intersecting a circular tissue slice are tested. For these 2D geometries vessel spacing, tissue radius and resolution are varied, as well as the position of the vessel pair with respect to the discretized tissue grid. The simulation results are evaluated by comparison of the different heat flow rates with analytical predictions. The tests show that for a fixed vessel configuration the accuracy is not a simple decreasing function of the voxel dimensions, but is also sensitive to the position of the configuration with respect to the discretized tissue grid.

Blood Vessels↗
PubMed1996

Dose uniformity in MECS interstitial hyperthermia: the impact of longitudinal control in model anatomies.

The quality of temperature distributions that can be generated with the multi-electrode current source (MECS) interstitial hyperthermia system, which allows 3D control of the spatial SAR distribution, has been investigated. For the investigations, computer models of idealized anatomies were used. These anatomical models did not contain discrete vessels. Binary-media anatomies, containing media interfaces oriented parallel, perpendicular or oblique with respect to the long axis of the implant, represent simple anatomies which can be encountered in the clinic. The implant volume was about 40 cm3. A seven-catheter hexagonal implant geometry with a nearest-neighbor distance of 15 mm was used. In each interstitial probe between one and four electrodes with a diameter of 2.1 mm were placed along an "active section' with a length of 50 mm. The electrode segments had lengths of 50, 20, 12 and 9 mm. This study shows that even with high contrasts in electrical and thermal conductivity in the implant it remains possible to obtain satisfactory temperature distributions with the MECS system. Due to its 3D spatial control the temperature homogeneity in the implant can be made quite satisfactory, with T10-T90 of the order of 2-3 K. Treatment planning must ensure that the placement of the current source electrodes is compatible with the media configuration.

Biophysical Phenomena↗
PubMed1994

The theoretical and experimental evaluation of the heat balance in perfused tissue.

Accurate treatment planning is necessary for the successful application of hyperthermia in the clinic. The validity of four different bioheat models or combinations of models is evaluated: the conventional bioheat transfer equation, the limited effective conductivity model, a mixed heat sink-effective conductivity model and a discrete vessel model. The heat balance for the heated volume, and especially the ratio between conductive heat removal and heat escape through the veins, is different for each of these models. Model predictions were compared with results from experiments on isolated perfused bovine tongues. Tongues were suspended in a water-filled container and heated by conduction. The steady state temperature distribution and heat balance were determined at various blood flow rates. Increased blood flow was found to lower the mean tissue temperature and to enhance both conductive and venous heat removal. This result agrees only with the mixed heat sink-effective conductivity and the discrete vessel model predictions. At low flow rates a modified heat sink term should be used because the venous efflux temperature was significantly lower than the mean tissue temperature.

Animals↗
PubMed1992

Temperature uniformity during hyperthermia: the impact of large vessels.

During hyperthermia the presence of a large vessel entering the heated volume and carrying blood at the systemic temperature can be an important source of temperature non-uniformity and possible underdosage. The minimal tumour temperature near a large vessel is determined by the vessel wall temperature: a number of factors influencing the vessel wall temperature are considered--effective tissue conductivity, flow type, vessel size, entrance effects and counter-current flow. In some specific cases, especially when tissue perfusion is high, the vessel wall temperature may reach therapeutic levels when the mean blood temperature is still low. In general, well perfused tumours have a better chance of being heated uniformly. Regional heating improves temperature uniformity by reducing entrance and equilibration effects as blood is heated before entering the tumour. Raising the core temperature also reduces temperature inhomogeneity. Spatial SAR resolution should preferably be of the order of magnitude of a centimetre or better.

Blood Vessels↗
PubMed1991

Interstitial heating: experiments in artificially perfused bovine tongues.

Isolated perfused bovine tongues were heated with a 2 x 2 hot water tube interstitial hyperthermia system (tube outer diameter 2.0 mm, spacing 16 mm). Tongue blood flow ranged between 0 and 17 ml min-1/100 g. The temperature distribution was mapped with 5 to 8 single thermocouples (diameter 50 microns). Model predictions using both the conventional bioheat transfer equation and the effective conductivity model were compared to the experimental results, with emphasis on the role of blood flow. Results indicate a better qualitative agreement with the k-effective model than with the heat sink model. In this set up a 16 mm spacing proved sufficient for adequate heating between the needles at normal blood flow rates, in the absence of large vessels.

Animals↗
PubMed1990

Experimental verification of bioheat transfer theories: measurement of temperature profiles around large artificial vessels in perfused tissue.

The verification of thermal models for use in hyperthermia treatment planning is essential. We investigated the heat transfer between a single vessel and the surrounding vascularised tissue, comparing the conventional bioheat transfer theory and the recently developed keff model using analytical and numerical methods. A plastic tube inserted into the tissue of an isolated perfused organ served as an artificial vessel. This enabled us to vary the blood flow in the vessel and in the tissue independently. The organ used was a bovine kidney, turned into a perfused tissue phantom using an alcohol fixation technique. The temperature profile within the tissue was mapped with constantan-manganin thermocouple wire sensors with a total diameter of 50 microns. The temperature profile relative to the temperature difference between the vessel and organ was measured; increased perfusion caused a reduction of the vessel wall temperature but did not affect the width of the profile. Studying the transient tissue temperature after a step-wise change of the blood temperature in the vessel revealed a faster diffusion of heat at higher perfusion rates. These facts are in accordance with the keff model, but not with the conventional heat-sink theory.

Animals↗