Experimental validation of MR-guided radiofrequency head and neck hyperthermia (original) (raw)
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Physics in Medicine and Biology, 2014
Clinical studies have established a strong benefit from adjuvant mild hyperthermia (HT) to radio-and chemotherapy for many tumor sites, including the head and neck (H&N). The recently developed HYPERcollar allows the application of local radiofrequency HT to tumors in the entire H&N. Treatment quality is optimized using electromagnetic and thermal simulators and, whenever placement risk is tolerable, assessed using invasively placed thermometers. To replace the current invasive procedure, we are investigating whether magnetic resonance (MR) thermometry can be exploited for continuous and 3D thermal dose assessment. In this work, we used our simulation tools to design an MR compatible laboratory prototype applicator. By simulations and measurements, we showed that the redesigned patch antennas are well matched to 50 (S11<−10 dB). Simulations also show that, using 300 W input power, a maximum specific absorption rate (SAR) of 100 W kg −1 and a temperature increase of 4.5 • C in 6 min is feasible at the center of a cylindrical fat/muscle phantom. Temperature measurements using the MR scanner confirmed the focused heating capabilities and MR compatibility of the setup. We conclude that the laboratory applicator provides the possibility for experimental assessment of the feasibility of hybrid MR-HT in the H&N region. This versatile design allows rigorous analysis of MR
Feasibility of MRI-guided hyperthermia treatment of head and neck cancer
The 8th European Conference on Antennas and Propagation (EuCAP 2014), 2014
Clinical studies have established a strong benefit from adjuvant mild hyperthermia to radio-and chemotherapy for many tumor sites, including the head and neck. The recently developed HYPERcollar allows applying local radiofrequency hyperthermia to tumors in the entire head and neck. Treatment quality is optimized using a combination of electromagnetic and temperature simulators and assessed using invasively placed thermometers. To replace the current invasive thermometry, we are investigating if magnetic resonance (MR) measurements can be exploited for continuous and 3D thermal dose assessment during treatment. In this study, we designed an MR compatible laboratory prototype applicator. We showed that the laboratory prototype applicator, based on re-designed patch antennas, enables MR guided focused heating and allows effective mitigating of image distortion. Hence, we conclude that hybrid MR-hyperthermia treatment in the head and neck region is feasible. The novel hybrid laboratory prototype further allows thorough investigation of patient and systems induced imaging distortions in preparation of the design of a clinical applicator.
International Journal of Hyperthermia, 2014
Magnetic resonance thermometry (MRT) offers non-invasive temperature imaging and can greatly contribute to the effectiveness of head and neck hyperthermia. We therefore wish to redesign the HYPERcollar head and neck hyperthermia applicator for simultaneous radio frequency (RF) heating and magnetic resonance thermometry. In this work we tested the feasibility of this goal through an exploratory experiment, in which we used a minimally modified applicator prototype to heat a neck model phantom and used an MR scanner to measure its temperature distribution. We identified several distorting factors of our current applicator design and experimental methods to be addressed during development of a fully MR compatible applicator. To allow MR imaging of the electromagnetically shielded inside of the applicator, only the lower half of the HYPERcollar prototype was used. Two of its antennas radiated a microwave signal (150 W, 434 MHz) for 11 min into the phantom, creating a high gradient temperature profile (DT max ¼ 5.35 C). Thermal distributions were measured sequentially, using drift corrected proton resonance frequency shift-based MRT. Measurement accuracy was assessed using optical probe thermometry and found to be about 0.4 C (0.1-0.7 C). Thermal distribution size and shape were verified by thermal simulations and found to have a good correlation (r 2 ¼ 0.76).
International Journal of Hyperthermia, 2021
Purpose: To develop a head and neck hyperthermia phased array system compatible with a 1.5 T magnetic resonance (MR) scanner for noninvasive thermometry. Methods: We designed a dielectric-parabolic-reflector antenna (DiPRA) based on a printed reflector backed dipole antenna and studied its predicted and measured performance in a flat configuration (30 mm thick water bolus and muscle equivalent layer). Thereafter, we designed a phased array applicator model ('MRcollar') consisting of 12 DiPRA modules placed on a radius of 180 mm. Theoretical heating performance of the MRcollar model was benchmarked against the current clinical applicator (HYPERcollar3D) using specific (3D) head and neck models of 28 treated patients. Lastly, we assessed the influence of the DiPRA modules on MR scanning quality. Results: The predicted and measured reflection coefficients (S 11) of the DiPRA module are below À20 dB. The maximum specific absorption rate (SAR) in the area under the antenna was 47% higher than for the antenna without encasing. Compared to the HYPERcollar3D, the MRcollar design incorporates 31% less demineralized water (À2.5 L), improves the predicted TC25 (target volume enclosed by 25% iso-SAR contour) by 4.1% and TC50 by 8.5%, while the target-to-hotspot quotient (THQ) is minimally affected (À1.6%). MR experiments showed that the DiPRA modules do not affect MR transmit/ receive performance. Conclusion: Our results suggest that head and neck hyperthermia delivery quality with the MRcollar can be maintained, while facilitating simultaneous noninvasive MR thermometry for treatment monitoring and control.
Physics in Medicine and Biology, 2010
To apply high-quality hyperthermia treatment to tumours at deep locations in the head and neck (H&N), we have designed and built a site-specific phased-array applicator. Earlier, we demonstrated its features in parameter studies, validated those by phantom measurements and clinically introduced the system. In this paper we will critically review our first clinical experiences and demonstrate the pivotal role of hyperthermia treatment planning (HTP). Three representative patient cases (thyroid, oropharynx and nasal cavity) are selected and discussed. Treatment planning, the treatment, interstitially measured temperatures and their interrelation are analysed from a physics point of view. Treatments lasting 1 h were feasible and well tolerated and no acute treatment-related toxicity has been observed. Maximum temperatures measured are in the range of those obtained during deep hyperthermia treatments in the pelvic region but mean temperatures are still to be improved. Further, we found that simulated power absorption correlated well with measured temperatures illustrating the validity of our treatment approach of using energy profile optimizations to arrive at higher temperatures. This is the first data proving that focussed heating of tumours in the H&N is feasible. Further, HTP proved a valuable tool in treatment optimization. Items to improve are (1) the transfer of HTP settings into the clinic and (2) the registration of the thermal dose, i.e. dosimetry.
MR monitoring of tumour thermal therapy
Magnetic Resonance Materials in Physics Biology and Medicine, 2001
Thermal therapy of tumour including hyperthermia and thermal ablation by heat or cold delivery requires on line monitoring. Due to its temperature sensitivity, Magnetic Resonance Imaging (MRI) allows thermal mapping at the time of the treatment. The different techniques of MR temperature monitoring based on water proton resonance frequency (PRF), longitudinal relaxation time Tl, diffusion coefficient and MR Spectroscopic Imaging
Status quo and directions in deep head and neck hyperthermia
The benefit of hyperthermia as a potent modifier of radiotherapy has been well established and more recently also the combination with chemotherapy was shown beneficial. Also for head and neck cancer, the impact of hyperthermia has been clinically demonstrated by a number of clinical trials. Unfortunately, the technology applied in these studies provided only limited thermal dose control, and the devices used only allowed treatment of target regions close to the skin. Over the last decade, we developed the technology for deep and controlled hyperthermia that allows treatment of the entire head and neck region. Our strategy involves focused microwave heating combined with 3D patient-specific electromagnetic and thermal simulations for conformal, reproducible and adaptive hyperthermia application. Validation of our strategy has been performed by 3D thermal dose assessment based on invasively placed temperature sensors combined with the 3D patient specific simulations. In this paper, we review the phase III clinical evidence for hyperthermia in head and neck tumors, as well as the heating and dosimetry technology applied in these studies. Next, we describe the development, clinical implementation and validation of 3D guided deep hyperthermia with the HYPERcollar, and its second generation, i.e. the HYPERcollar3D. Lastly, we discuss early clinical results and provide an outlook for this technology.
International Journal of Radiation Oncology*Biology*Physics, 2005
Purpose: This study investigates the feasibility and accuracy of noninvasive magnetic resonance (MR) monitoring for a system that includes a multiantenna applicator for part-body hyperthermia (SIGMA-Eye applicator, BSD-2000/3D) and a 1.5 Tesla MR tomograph (Siemens Magnetom Symphony). Methods: A careful electrical decoupling enabled simultaneous operation of both systems, the hyperthermia system (100 MHz, up to 1600 W) and the MR tomograph (63.9 MHz). We used the phase data sets of a gradient echo sequence (long echo time TE ؍ 20 ms) according to the proton frequency shift (PFS) method to determine MR temperature changes. Data postprocessing and visualization was conducted in the software platform AMIRA-HyperPlan. Heating was evaluated in an elliptical Lucite cylinder of 50 cm length filled with tissueequivalent agarose and a skeleton made from low-dielectric material to simulate the heterogeneity of a real patient. Multiple catheters were included longitudinally for direct thermometry (using Bowman high-impedance thermistors). The phantom was positioned in the 24-antenna applicator SIGMA-Eye employing the integrated water bolus (filled with deionized water) both for coupling the radiated power into the lossy medium and to enable a correction procedure based on direct temperature measurements. Results: In eight phantom experiments we monitored the heating in the applicator not only by repetitive acquisition of three-dimensional MR datasets, but also by measuring temperature-time curves directly at selected spatial positions. For the correction, we specified regions in the bolus. Direct bolus temperatures at fixed positions were taken to aim at best possible agreement between MR temperatures and these direct temperature-time curves. Then we compared additional direct temperature-position scans (thermal maps) for each experiment with the MR temperatures along these probes, which agreed satisfactorily (averaged accuracy of ؎ 0.4-0.5°C). The deviations decreased with decreasing observation time, temperature increase, and thermal load to the surroundings (corresponding to bolus heating)-estimating a resolution of, at best, ؎ 0.2-0.3°C. The acquired MR temperature distributions give also insight into limitations and control possibilities of regional hyperthermia (annular phased array technology) for various tumor sites. Conclusions: On-line MR monitoring of regional hyperthermia by using the PFS method is feasible in a phantom setup and can be further developed for clinical applications.
Single radiofrequency source for MR and hyperthermia studies
Hyperthermia is an experimental/adjuvant therapeutic modality for cancer. Combining hyperthermia with the non-invasive metabolic studies using magnetic resonance (MR) is an interesting area of research and can provide useful information. In this paper, feasibility of using the same radio frequency source for carrying out combined hyperthermia and MR studies is demonstrated. A conventional RF hyperthermic applicator has been evaluated for use as an MR transmit/receive coil.
Non-invasive magnetic resonance thermography during regional hyperthermia
International Journal of Hyperthermia, 2010
To implement noninvasive thermometry, we installed a hybrid system consisting of a radiofrequency multiantenna applicator (SIGMA-Eye) for deep hyperthermia (BSD-2000/3D) integrated into the gantry of a 1.5 Tesla magnetic resonance (MR) tomograph Symphony. This system can record MR data during radiofrequency heating and is suitable for application and evaluation of methods for MR thermography. In 15 patients with preirradiated pelvic rectal recurrences, we acquired phase data sets (25 slices) every 10 to 15 minutes over the treatment time (60-90 minutes) using gradient echo sequences (echo time = 20 ms), transformed the phase differences to MR temperatures, and fused the color-coded MR-temperature distributions with anatomic T1-weighted MR data sets. We could generate one complete series of MR data sets per patient with satisfactory quality for further analysis. In fat, muscle, water bolus, prostate, bladder, and tumor, we delineated regions of interest (ROI), used the fat ROI for drift correction by transforming these regions to a phase shift zero, and evaluated the MR-temperature frequency distributions. Mean MR temperatures (T MR ), maximum T MR , full width half maximum (FWHM), and other descriptors of tumors and normal tissues were noninvasively derived and their dependencies outlined. In 8 of 15 patients, direct temperature measurements in reference points were available. We correlated the tumor MR temperatures with direct measurements, clinical response, and tumor features (volume and location), and found reasonable trends and correlations. Therefore, the mean T MR of the tumor might be useful as a variable to evaluate the quality and effectivity of heat treatments, and consequently as optimization variable. Feasibility of noninvasive MR thermography for regional hyperthermia has been shown and should be further investigated. (Cancer Res 2005; 65(13): 5872-80) Requests for reprints: