J. Sijbrands

Improving locoregional hyperthermia delivery using the 3-D controlled AMC-8 phased array hyperthermia system: A preclinical study

Background: The aim of this study is preclinical evaluation of our newly developed regional hyperthermia system providing 3-D SAR control: the AMC-8 phased array consisting of two rings, each with four 70 MHz waveguides. It was designed to achieve higher tumour temperatures and improve the clinical effectiveness of locoregional hyperthermia. Methods: The performance of the AMC-8 system was evaluated with simulations and measurements aiming at heating a centrally located target region in rectangular (30 × 30 × 110 cm) and elliptical (36 × 24 × 80 cm) homogeneous tissue equivalent phantoms. Three properties were evaluated and compared to its predecessor, the 2-D AMC-4 single ring four waveguide array: (1) spatial control and (2) size of the SAR focus, (3) the ratio between maximum SAR outside the target region and SAR in the focus. Distance and phase difference between the two rings were varied. Results: (1) Phase steering provides 3-D SAR control for the AMC-8 system. (2) The SAR focus is more elongated compared to the AMC-4 system, yielding a lower SAR level in the focus when using the same total power. This is counter-balanced by (3) a superficial SAR deposition which is half of that in the AMC-4 system, yielding a more favourable ratio between normal tissue and target SAR and allowing higher total power and up to 30% more SAR in the focus for 3 cm ring distance. Conclusion: The AMC-8 system is capable of 3-D SAR control and its SAR distribution is more favourable than for the 2-D AMC-4 system. This result promises improvement in clinical tumour temperatures.

Novel Multisensor Probe for Monitoring Bladder Temperature During Locoregional Chemohyperthermia for Nonmuscle-Invasive Bladder Cancer: Technical Feasibility Study

BACKGROUND AND PURPOSE The effectiveness of locoregional hyperthermia combined with intravesical instillation of mitomycin C to reduce the risk of recurrence and progression of intermediate- and high-risk nonmuscle-invasive bladder cancer is currently investigated in clinical trials. Clinically effective locoregional hyperthermia delivery necessitates adequate thermal dosimetry; thus, optimal thermometry methods are needed to monitor accurately the temperature distribution throughout the bladder wall. The aim of the study was to evaluate the technical feasibility of a novel intravesical device (multi-sensor probe) developed to monitor the local bladder wall temperatures during loco-regional C-HT. MATERIALS AND METHODS A multisensor thermocouple probe was designed for deployment in the human bladder, using special sensors to cover the bladder wall in different directions. The deployment of the thermocouples against the bladder wall was evaluated with visual, endoscopic, and CT imaging in bladder phantoms, porcine models, and human bladders obtained from obduction for bladder volumes and different deployment sizes of the probe. Finally, porcine bladders were embedded in a phantom and subjected to locoregional heating to compare probe temperatures with additional thermometry inside and outside the bladder wall. RESULTS The 7.5 cm thermocouple probe yielded optimal bladder wall contact, adapting to different bladder volumes. Temperature monitoring was shown to be accurate and representative for the actual bladder wall temperature. CONCLUSIONS Use of this novel multisensor probe could yield a more accurate monitoring of the bladder wall temperature during locoregional chemohyperthermia.

Improving hyperthermia treatment planning for the pelvis by accurate fluid modeling.

PURPOSE Hyperthermia is an established (neo)adjuvant treatment modality for a number of pelvic malignancies. Optimal treatment of these tumors requires robust treatment planning, but up until now, the urinary bladder was not modeled accurately, making current simulations less reliable. The authors improved the dielectric and thermophysical model of the urinary bladder in their treatment planning system, and showed the improvements using phantom experiments. METHODS The authors suspended a porcine bladder in muscle tissue equivalent gel and filled it with 120 ml 0.9% saline. The authors heated the phantom during 15 min with their deep hyperthermia device, using clinical settings, and measured the temperature both inside and outside the bladder. The authors simulated the experiment, both using the clinically used treatment planning system, and using the improved model featuring correct dielectric properties for the bladder content and an enhanced thermophysical model, enabling the simulation of convection. RESULTS Although the dielectric changes have an impact throughout the phantom, the dominant effect is a higher net heat absorption in the bladder. The effects of changing the thermophysical model are limited to the bladder and its surroundings, but result in a very different temperature profile. The temperatures predicted by the simulations using the new bladder model were in much better agreement with the measurements than those predicted by currently used treatment planning system. CONCLUSIONS Modeling convection in the urinary bladder is very important for accurate hyperthermia treatment planning in the pelvic area.

Comparison of two different 70 MHz applicators for large extremity lesions: Simulation and application

Introduction: Motivation for this research was a patient with large and bulky melanoma lesions on a leg, treated with hyperthermia in a special set-up with an open water bolus and two opposing applicators. Treatment planning was used to find the most suitable heating method, comparing 70 MHz capacitive contact flexible microstrip applicators (CFMAs) and 70 MHz waveguides. Methods: The first three sessions were performed with CFMA applicators; the last session with waveguides. Power and water temperature were adjusted to achieve clinically relevant temperatures. Finite difference time domain (FDTD) simulations were performed for a CFMA and waveguide on a fat-muscle geometry to compare effective field size (EFS) and effective heating depth (EHD). A CT scan of the patients leg was automatically segmented into muscle, fat and bone; tumour lesions were outlined manually. Patient simulations were performed to evaluate the 3D heating pattern and to compare CFMAs and waveguides for equal power and water temperature. Results: Hyperthermia treatment was well tolerated. Temperature measurements indicated mainly superficial heating with CFMAs. Simulated EHD was 2.1 and 2.4 cm for CFMA and waveguide, respectively and EFS was 19.6 × 16.2 cm2 and 19.4 × 16.3 cm2. Simulation results showed a better tumour coverage using waveguides; absorbed power in the tumour was ∼75% higher with waveguides and absorption in fat was approximately twice as high with CFMAs. Simulations showed that a relatively high water temperature (∼42°C) improves the overall temperature distribution. Conclusion: CFMAs and waveguides have a similar EFS and EHD, but for large extremity lesions, the performance of 70 MHz waveguides is favourable compared to 70 MHz CFMA applicators.

Development of a 70 MHz unit for hyperthermia treatment of deep-seated breast tumors

Hyperthermia of tumors in intact breast extending beyond the heating depth of our superficial 434 MHz CFMA antennas requires an alternative approach. A dedicated system was designed for this purpose, consisting of a treatment bed fitted with a 50×40×16cm temperature controlled open water bolus. The patient lies in prone position with the breast immersed in the water positioned in front of a 34×20cm 70 MHz waveguide placed in the bottom of the bolus. Hyperthermia was applied once a week for the whole breast with the 70 MHz applicator for 6 patients treated with thermoradiotherapy for deep lesions of recurrent breast cancer or melanoma. Two 14-sensor thermocouple thermometry probes were placed in catheters to monitor the invasive temperature. Results: The combination of 300–900W antenna power and a water temperature of 42°C was well tolerated for the entire session of one hour and resulted in good tumor temperatures with T10 = 42.2°C, T50 = 41.1°C, T90 = 39.8°C. No toxicity or complaints were associated with the heating. A water mattress and other measures were needed to assure a comfortable position throughout the treatment. Conclusion: the 70 MHz breast applicator system performed well and tumor temperatures were good.

A flexible 70 MHz phase-controlled double waveguide system for hyperthermia treatment of superficial tumours with deep infiltration

Abstract Purpose: Superficial tumours with deep infiltration in the upper 15 cm of the trunk cannot be treated adequately with existing hyperthermia systems. The aim of this study was to develop, characterise and evaluate a new flexible two-channel hyperthermia system (AMC-2) for tumours in this region. Materials and methods: The two-channel AMC-2 system has two horizontally revolving and height adjustable 70 MHz waveguides. Three different interchangeable antennas with sizes 20 × 34, 15 × 34 and 8.5 × 34 cm were developed and their electrical properties were determined. The performance of the AMC-2 system was tested by measurements of the electric field distribution in a saline water filled elliptical phantom, using an electric field vector probe. Clinical feasibility was demonstrated by treatment of a melanoma in the axillary region. Results: Phantom measurements showed a good performance for all waveguides. The large reflection of the smallest antenna has to be compensated by increased forward power. Field patterns become asymmetrical when using smaller top antennas, necessitating phase corrections. The clinical application showed that tumours deeper than 4 cm can be heated adequately. A median tumour temperature of 42 °C can be reached up to 12 cm depth with adequate antenna positioning and phase-amplitude steering. Conclusions: This 70 MHz AMC-2 waveguide system is a useful addition to existing loco-regional hyperthermia equipment as it is capable of heating axillary tumours and other tumours deeper than 4 cm.

Visualization of interfering RF-electric fields in a lossy liquid simulating a patient's body in a hyperthermia treatment by a LED-matrix

Matrices Of LED-dipoles have been constructed as a cheap and easy-to-use tool for Quality Assurance in deep body hyperthermia. Placed inside a phantom, i.e. a watertank filled with saline, one type of LED-matrix visualizes axial E-field components, the other one both radial components of the E-field. By moving of the matrix plate, the components of the E-field can be monitored in the complete inner volume of the phantom. Due to the feature of measurements in real time, LED-matrices are especially suitable to check numerous variations of set-up parameters as e.g. phase and amplitude settings as well as the performance of deep body hyerthermia systems in clinical routine.