525 research outputs found
Overview of bladder heating technology: matching capabilities with clinical requirements.
Moderate temperature hyperthermia (40-45°C for 1 h) is emerging as an effective treatment to enhance best available chemotherapy strategies for bladder cancer. A rapidly increasing number of clinical trials have investigated the feasibility and efficacy of treating bladder cancer with combined intravesical chemotherapy and moderate temperature hyperthermia. To date, most studies have concerned treatment of non-muscle-invasive bladder cancer (NMIBC) limited to the interior wall of the bladder. Following the promising results of initial clinical trials, investigators are now considering protocols for treatment of muscle-invasive bladder cancer (MIBC). This paper provides a brief overview of the devices and techniques used for heating bladder cancer. Systems are described for thermal conduction heating of the bladder wall via circulation of hot fluid, intravesical microwave antenna heating, capacitively coupled radio-frequency current heating, and radiofrequency phased array deep regional heating of the pelvis. Relative heating characteristics of the available technologies are compared based on published feasibility studies, and the systems correlated with clinical requirements for effective treatment of MIBC and NMIBC
Elektromagnetische velden: geen ontkomen aan
Rede,
in verkorte vorm uitgesproken
ter gelegenheid van het aanvaarden
van het ambt van bijzonder hoogleraar
met als leeropdracht Fysische aspecten van
elektromagnetische velden en gezondheid
aan het Erasmus MC, faculteit van de
Erasmus Universiteit Rotterdam
op 17 november 2011
Tegenwoordig begint elk concert of theater met het verzoek te controleren of de
mobiele telefoon is uitgezet. In de figuur (1) kunt u zien hoe het bezit van mobiele
telefoons in de afgelopen jaren is gestegen. In het tweede kwartaal van 2011 waren er
in Nederland 21 miljoen mobiele telefoons aangesloten. Dit betekent dat de gemiddelde
Nederlander inmiddels meer dan één mobiele telefoonverbinding tot zijn of haar
beschikking heeft.
Natuurlijk moeten al die mobiele telefoons ook een verbinding hebben met het
netwerk. Daarvoor is Nederland voorzien van een groot aantal zendmasten. Meestal
veroorzaakt het plaatsen van een zendmast veel onrust. Een uitzondering hierop zijn
de bewoners van Goudswaard. Maar liefst 1200 inwoners tekenden een petitie vóór
het plaatsen van een UMTS zendmast. Duidelijk is dat we zeer gehecht zijn aan een
constante beschikbaarheid van de mobiele communicatie middelen. Als een vliegtuig
nog maar net met de banden de grond raakt, dan reiken veel passagiers alweer naar
hun telefoon om de verbinding zo snel mogelijk te herstellen
Using a Conformal Water Bolus to Adjust Heating Patterns of Microwave Waveguide Applicators
Background: Hyperthermia, i.e., raising tissue temperature to 40-45°C for 60 min, has been demonstrated to increase the effectiveness of radiation and chemotherapy for cancer. Although multi-element conformal heat applicators are under development to provide more adjustable heating of contoured anatomy, to date the most often used applicator to heat superficial disease is the simple microwave waveguide. With only a single power input, the operator must be resourceful to adjust heat treatment to accommodate variable size and shape tumors spreading across contoured anatomy. Methods: We used multiphysics simulation software that couples electromagnetic, thermal and fluid dynamics physics to simulate heating patterns in superficial tumors from commercially available microwave waveguide applicators. Temperature distributions were calculated inside homogenous muscle and layered skin-fat-muscle-tumor-bone tissue loads for a typical range of applicator coupling configurations and size of waterbolus. Variable thickness waterbolus was simulated as necessary to accommodate contoured anatomy. Physical models of several treatment configurations were constructed for comparison of simulation results with experimental specific absorption rate (SAR) measurements in homogenous muscle phantom. Results: Accuracy of the simulation model was confirmed with experimental SAR measurements of three unique applicator setups. Simulations demonstrated the ability to generate a wide range of power deposition patterns with commercially available waveguide antennas by controllably varying size and thickness of the waterbolus layer. Conclusion: Heating characteristics of 915 MHz waveguide antennas can be varied over a wide range by controlled adjustment of microwave power, coupling configuration, and waterbolus lateral size and thickness. The uniformity of thermal dose delivered to superficial tumors can be improved by cyclic switching of waterbolus thickness during treatment to proactively shift heat peaks and nulls around under the aperture, thereby reducing patient pain while increasing minimum thermal dose by end of treatment. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE)
Comparison of intratumor and intraluminal temperatures during locoregional deep hyperthermia of pelvic tumors
Purpose: To investigate whether intraluminal thermometry provides sufficient information to apply high quality deep hyperthermia in pelvic tumors. Patients and Methods: The intratumor and intraluminal temperatures of 48 patients were analyzed per cancer type: rectum (21 male, 14 female), cervix (n = 8), and bladder (n = 5). Temperature-dose parameters were calculated, temperature curves within each treatment session were compared, and correlation between intratumor and intraluminal temperatures was analyzed. Results: Intratumor and intraluminal temperatures at the same time points during individual treatments were highly correlated (mean correlation coefficient: 0.93). However, the quantitative level differed from 0.1 to 1.1 degrees C and the differences of the timetemperature graphs varied per tumor group. Average intratumor and intraluminal temperatures were not different in the four groups. Intratumor thermometry was found not superior over intraluminal thermometry to improve tumor temperature level and homogeneity by SAR steering. Conclusion: Intraluminal thermometry provides sufficient information to apply deep hyperthermia to individual patients with centrally located rectum, cervix or bladder cancer
An Electromagnetic Head and Neck Hyperthermia Applicator: experimental phantom verification and FDTD model
Purpose: To experimentally verify the feasibility of focused heating in the neck region by an array of two rings of six electromagnetic antennas. We also measured the dynamic specific absorption rate (SAR) steering possibilities of this setup and compared these SAR patterns to simulations.
Methods and Materials: Using a specially constructed laboratory prototype head-and-neck applicator, including
a neck-mimicking cylindrical muscle phantom, we performed SAR measurements by electric field, Schottkydiode sheet measurements and, using the power-pulse technique, by fiberoptic thermometry and infrared thermography. Using phase steering, we also steered the SAR distribution in radial and axial directions. All
measured distributions were compared with the predictions by a finite-difference time-domain–based electromagnetic
simulator.
Results: A central 50% iso-SAR focus of 35 +/- 3 mm in diameter and about 100 +/- 15 mm in length was obtained for all investigated settings. Furthermore, this SAR focus could be steered toward the desired location in the radial and axial directions with an accuracy of ~5 mm. The SAR distributions as measured by all three
experimental methods were well predicted by the simulations.
Conclusion: The results of our study have shown that focused heating in the neck is feasible and that this focus can be effectively steered in the radial and axial directions. For quality assurance measurements, we believe that the Schottky-diode sheet provides the best compromise among effort, speed, and accuracy, although a more specific and improved design is warranted
A moderate thermal dose is sufficient for effective free and TSL based thermochemotherapy
Hyperthermia, i.e. heating the tumor to a temperature of 40–43 °C is considered by many a valuable treatment to sensitize tumor cells to radiotherapy and chemotherapy. In recent randomized trials the great potential of adding hyperthermia to chemotherapy was demonstrated for treatment of high risk soft tissue sarcoma: +11.4% 5 yrs. overall survival (OS) and for ovarian cancer with peritoneal involvement nearly +12 months OS gain. As a result interest in combining chemotherapy with hyperthermia, i.e. thermochemotherapy, is growing. Extensive biological research has revealed that hyperthermia causes multiple effects, from direct cell kill to improved oxygenation, whereby each effect has a specific temperature range. Thermal sensitization of the tumor cell for chemotherapy occurs for many drugs at temperatures ranging from 40 to 42 °C with little additional increase of sensitization at higher temperatures. Increasing perfusion/oxygenation and increased extravasation are two other important hyperthermia induced mechanisms. The combination of free drug and hyperthermia has not been found to increase tumor drug concentration. Hence, enhanced effectiveness of free drug will de
Assessment of the local SAR Distortion by Major Anatomical Structures in a Cylindrical Neck Phantom
The objective of this work is to gain insight in the distortions on the local SAR distribution by various major anatomical structures in the neck. High resolution 3D FDTD calculations based on a variable grid are made for a semi-3D generic phantom based on average dimensions obtained from CT-derived human data and in which simplified structures representing trachea, cartilage, spine and spinal cord are inserted. In addition, phantoms with dimensions equal to maximum and minimum values within the CT-derived data are also studied. In all cases, the phantoms are exposed to a circular coherent array of eight dipoles within a water bolus and driven at 433 MHz. Comparisons of the SAR distributions due to individual structures or a combination of structures are made relative to a cylindrical
phantom with muscle properties. The calculations predict a centrally located region of high SAR within all neck phantoms. This focal region, expressed as contours at either 50% or 75% of the peak SAR, changes from a circular cross-section in the case of the muscle phantom to a doughnut
shaped region when the anatomical structures are present. The presence of the spine causes the greatest change in the SAR distribution, followed closely by the trachea. Global changes in the mean SAR relative to the uniform phantom are <11%, whilst local changes are as high as 2.7-fold. There is little difference in the focal dimensions between the average and smallest phantoms, but a decrease in the focal region is seen in the case of the largest phantom. This study presents a first step towards understanding of the complex influences of the various parameters on the SAR pattern
which will facilitate the design of a site-specific head and neck hyperthermia applicator
A head and neck hyperthermia applicator: Theoretical antenna array design
Purpose: Investigation into the feasibility of a circular array of dipole antennas to deposit RF-energy centrally in the neck
as a function of: (1) patient positioning, (2) antenna ring radius, (3) number of antenna rings, (4) number of antennas per
ring and (5) distance between antenna rings.
Materials and Methods: Power absorption (PA) distributions in realistic, head and neck, anatomy models are calculated
at 433 MHz. Relative PA distributions corresponding to different set-ups were analysed using the ratio of the average
PA (aPA) in the target and neck region.
Results: Enlarging the antenna ring radius from 12.5cm to 25 cm resulted in a ~21% decrease in aPA. By changing the
orientation of the patients with respect to the array an increase by ~11% was obtained. Increase of the amount of antenna
rings led to a better focussing of the power (1 - 2 / 3: ~17%). Increase of the distance between the antenna rings resulted in a
smaller (more target region conformal) focus but also a decreased power penetration.
Conclusions: A single optimum array setup suitable for all patients is difficult to define. Based on the results and practical
limitations a setup consisting of two rings of six antennas with a radius of 20 cm and 6 cm array spacing is considered a good
choice providing the ability to heat the majority of patients
The potential of time-multiplexed steering by temperature optimization in microwave hyperthermia
Introduction: In clinical practice at Erasmus MC, the target-to-hotspot-quotient (THQ) of the specific absorption rate (SAR) is used to optimize phases and amplitudes of the signals to be applied to the hyperthermia applicator [1]. Recent research showed that the ratio between tumor and healthy tissue temperatures can be increased when amplitudes and phases are time-multiplexed when applying SAR optimization [2]. However, direct temperature optimization achieves higher tumor temperatures when considering time-multiplexed antenna steering [3]. In this work, we investigated the benefit of time-multiplexed steering when applying temperature optimization in models of patients with tumors on the head and neck region. Methods: For five patients with a tumor in the head and neck region, a Sim4Life model was created and treatment planning was applied for the HyperCollar3D. A single distribution SAR based THQ optimization was performed for reference. A novel temperature optimization scheme was developed, which optimizes the tumor temperature for the first 15 minutes of the treatment. This results in higher tumor temperatures throughout the treatment by explicitly including the transient effects in the optimization. The evaluation was based on simulations of the full treatment time of 75 minutes, with the total power scaled to reach maximum 43°C in the tumor. Performance was evaluated by comparing T50 for both healthy and tumor tissue during treatment. Results: The ratio between T50 in the healthy and tumor tissue was improved when using the novel temperature-based optimization for time-multiplexed distributions (Figure 1C). The SAR THQ showed a lower ratio for the time-multiplexed solution, this is resolved in the temperature simulations (Figure 2).Conclusion/Discussion: The resulting T50 values, show that the temperatures during treatment might benefit from the temperature optimized with the multiplexed steering approach: either the temperature in the tumor tissue can be higher or the temperature in healthy tissue could remain lower. Although the approach seems beneficial, assessment of the impact of uncertainties in thermal parameters and inclusion of a larger dataset is still required to assess the significance of the improvement and the expected clinical benefit [4]. <br/
A Patch Antenna Design for Application in a Phased-Array Head and Neck Hyperthermia Applicator
In this paper, we describe a specifically designed patch antenna that can be used as the basis antenna element of a clinical phased-array head and neck hyperthermia applicator. Using electromagnetic simulations we optimized the dimensions
of a probe-fed patch antenna design for operation at 433 MHz. By several optimization steps we could converge to a theoretical reflection of -38 dB and a bandwidth (-15 dB) of 20 MHz
(4.6%). Theoretically, the electrical performance of the antenna was satisfactory over a temperature range of 15 C–35 C, and stable for patient-antenna distances to as low as 4 cm. In an experimental cylindrical setup using six elements of the final patch design, we measured the impedance characteristics of the antenna 1) to establish its performance in the applicator and 2) to validate the simulations. For this experimental setup we simulated and measured comparable values: -21 dB reflection at 433 MHz and a bandwidth of 18.5 MHz. On the basis of this study, we anticipate good central interference of the fields of multiple antennas and conclude that this patch antenna design is very suitable for
the clinical antenna array. In future research we will verify the electrical performance in a prototype applicator
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