Rhoon, G.C. van

Elektromagnetische velden: geen ontkomen aan (Inaugural Lecture)

2011-11-17T00:00:00Z

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.

The clinical feasibility of deep hyperthermia treatment in the head and neck (Article)

2010-04-06T00:00:00Z

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 reviewour 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.

Triggered content release from optimized stealth thermosensitive liposomes using mild hyperthermia (Article)

2010-04-01T00:00:00Z

Liposomes are potent nanocarriers to deliver chemotherapeutic drugs to tumors. However, the inefficient drug release hinders their application. Thermosensitive liposomes (TSL) can release drugs upon heat. This study aims to identify the optimum 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-PEG2000(DSPE-PEG2000) concentration in stealth TSL to improve content release efficiency under mild hyperthermia (HT). TSL were prepared with DSPE-PEG2000from 1 to 10mol%, around 80nm in size. Quenched carboxyfluorescein (CF) in aqueous phase represented encapsulated drugs. In vitro temperature/time-dependent CF release and TSL stability in serum were quantified by fluorometry. In vivo CF release in dorsal skin flap window chamber models implanted with human BLM melanoma was captured by confocal microscopy. In vitro heat triggered CF release increased with increasing DSPE-PEG2000density. However, 6mol% and higher DSPE-PEG2000caused CF leakage at physiological temperature. TSL with 5mol% DSPE-PEG2000were stable at 37°C, while released 60% CF in 1min and almost 100% CF in 1h at 42°C. In vivo optical intravital imaging showed immediate massive CF release above 41°C. In conclusion, incorporation of 5mol% DSPE-PEG2000optimized stealth TSL content release triggered by HT.

Design and test of a 434 MHz multi-channel amplifier system for targeted hyperthermia applicators (Article)

2010-02-26T00:00:00Z

Purpose: For our head-and-neck hyperthermia (HT) applicator, an amplifier system with full amplitude and phase-control to deliver the radio-frequency signals, was not available. We therefore designed and tested a 433.92 MHz multi-channel amplifier system. System description: The design consists of a direct digital synthesizer (DDS) system that generates 12 phase-controlled coherent 433.92 MHz signals, which are amplified to maximum 200 W output per channel. Directional couplers are placed at the amplifiers to couple a small portion of both forward and reflected signals to gain-and-phase detectors. The power setting is applied with a resolution of 2 W and for the phase it is 0.1°. The channels are sequentially sampled at 100 Hz per channel. Methods: We tested the performance of the designed amplifier system by measuring the RF spectrum, power and phase accuracy, and by characterising the feedback control by using highly accurate power and phase meters. Results: The spurious emission is less than 60 dBc and the first two harmonic frequencies are suppressed more than 45 dB. The measurement accuracy for the power (±5%) is valid for at least 20 days after calibration and for the phase (±5%°) it is valid for at least 2 months. Conclusions: The amplifier system operates according to our design criteria to support targeted HT. It can be used for both our in-house developed superficial and head-and-neck HT applicators or any other HT applicator that works on the same frequency of 433.92 MHz.

Clinical implementation of hyperthermia treatment planning guided steering: A cross over trial to assess its current contribution to treatment quality (Article)

2010-02-26T00:00:00Z

Purpose: To assess the current feasibility of online hyperthermia treatment planning guided steering (HGS) and its current contribution to treatment quality in deep hyperthermia for locally advanced cervical cancer. Materials and methods: 36 patients were randomized to receive either their second and fourth (arm A) or their third and fifth (arm B) hyperthermia treatment of the series with the aid of HGS. The other treatments were conducted according to the Rotterdam Empirical Steering Guidelines (RESG). Results: During period I (second and third treatment of the series) similar results were found for HGS and RESG with a slight, non-significant difference found in favour of HGS. The average temperature T50 was 40.3°C for both (p=0.409) and the dose parameter CEM43T90 was 0.64 for RESG and 0.63 for HGS (p=0.154). However, during period II (fourth and fifth treatment of the series) HGS performed less well, with significant lower thermal dose parameters, minimum, mean and maximum intraluminal temperatures, tolerance measures and net integrated power. T50 was 40.4°C after RESG and 40°C after HGS (p=0.001) and CEM43T90 0.57 and 0.38 (p=0.01) respectively. Conclusion: We found that the procedure of online treatment planning guided steering is feasible. For maximal exploitation of its possibilities, however, better control and understanding of several patient, tumour and technical parameters is required. This study has been very helpful in identifying some of the challenges and flaws that warrant further investigation in the near future, such as patient positioning and the prevention of hotspot-related complaints.

The clinical feasibility of deep hyperthermia treatment in the head and neck (Article)

2010-01-01T00:00:00Z

A literature survey on indicators for characterisation and optimisation of SAR distributions in deep hyperthermia, a plea for standardisation (Article)

2009-12-21T00:00:00Z

Purpose: To evaluate the predictive value of SAR indicators by assessing the correlation of a SAR indicator with the corresponding predicted temperature. Ultimately, this should lead to a number of verified SAR indicators for characterization and optimization of a predicted SAR distribution. Methods: A literature survey is followed by an evaluation of the SAR indicators on their functionality, using a set of heuristic classification criteria. To obtain an objective assessment of the predictive value for SAR characterisation, all SAR indicators are evaluated by correlating the value of the SAR indicator to the predicted target temperature when heated with the BSD2000 Sigma 60 applicator. Two methods were followed. First, the specificity of the SAR indicator to target temperature was assessed for each of the 36 patient-specific models, using 30 randomly chosen phase and amplitude settings. Secondly, each SAR indicator was used as a goal function to assess its suitability for optimisation purposes. Results: Only a selected number of SAR indicators correlate well with tumour/target-temperature. Hence, for target-related properties, an adequate set of SAR indicators is found in the literature. For hotspots, modifications are desirable. For optimisation purposes, improved objective functions have been defined. Conclusions: From the correlation of the SAR indicators with tumour temperature, a preferred set of SAR indicators is derived: For target heating, 'average SAR ratio', 'Hotspot-target SAR ratio', and 'homogeneity coefficient' provide suitable objective criteria, while for hotspot reduction, 'Hotspot-target SAR ratio' is considered the most useful indicator. For optimisation procedures, 'Hotspot-target SAR ratio' is currently the most suitable objective function.

Hyperthermia dose-effect relationship in 420 patients with cervical cancer treated with combined radiotherapy and hyperthermia (Article)

2009-07-01T00:00:00Z

Adding hyperthermia to standard radiotherapy (RT + HT) improves treatment outcome for patients with locally advanced cervical cancer (LACC). We investigated the effect of hyperthermia dose on treatment outcome for patients with LACC treated with RT + HT. We collected treatment and outcome data of 420 patients with LACC treated with hyperthermia at our institute from 1990 to 2005. Univariate and multivariate analyses were performed on response rate, local control, disease-specific survival and toxicity for these patients to search for a thermal dose response relationship. Besides commonly identified prognostic factors in LACC like tumour stage, performance status, radiotherapy dose and tumour size, thermal parameters involving both temperature and duration of heating emerged as significant predictors of the various end-points. The more commonly used CEM43T90 (cumulative equivalent minutes of T90 above 43 °C) was less influential than TRISE (based on the average T50 increase and the duration of heating, normalised to the scheduled duration of treatment). CEM43T90 and TRISE measured intraluminally correlate significantly and independently with tumour control and survival. These findings stimulate further technological development and improvement of deep hyperthermia, as they strongly suggest that it might be worthwhile to increase the thermal dose for LACC, either by treatment optimisation or by prolonging the treatment time. These results also confirm the beneficial effects from hyperthermia as demonstrated in our earlier randomised trial, and justify applying radiotherapy and hyperthermia as treatment of choice for patients with advanced cervical cancer.

Radiotherapy and Hyperthermia for Treatment of Primary Locally Advanced Cervix Cancer: Results in 378 Patients (Article)

2009-01-01T00:00:00Z

Purpose: To report response rate, pelvic tumor control, survival, and late toxicity after treatment with combined radiotherapy and hyperthermia (RHT) for patients with locally advanced cervical carcinoma (LACC) and compare the results with other published series. Methods and Materials: From 1996 to 2005, a total of 378 patients with LACC (International Federation of Gynecology and Obstetrics Stage IB2-IVA) were treated with RHT. External beam radiotherapy (RT) was applied to 46-50.4 Gy and combined with brachytherapy. The hyperthermia (HT) was prescribed once weekly. Primary end points were complete response (CR) and local control. Secondary end points were overall survival, disease-specific survival, and late toxicity. Patient, tumor, and treatment characteristics predictive for the end points were identified in univariate and multivariate analyses. Results: Overall, a CR was achieved in 77% of patients. At 5 years, local control, disease-specific survival, and incidence of late toxicity Common Terminology Criteria for Adverse Events Grade 3 or higher were 53%, 47%, and 12%, respectively. In multivariate analysis, number of HT treatments emerged as a predictor of outcome in addition to commonly identified prognostic factors. Conclusions: The CR, local control, and survival rates are similar to previously observed results of RHT in the randomized Dutch Deep Hyperthermia Trial. Reported treatment results for currently applied combined treatment modalities (i.e., RT with chemotherapy and/or HT) do not permit definite conclusions about which combination is superior. The present results confirm previously shown beneficial effects from adding HT to RT and justify the application of RHT as first-line treatment in patients with LACC as an alternative to chemoradiation.

Steering in locoregional deep hyperthermia: Evaluation of common practice with 3D-planning (Article)

2008-12-22T00:00:00Z

Purpose: In Rotterdam, fifteen years of clinical experience with deep hyperthermia has sublimated in empirical treatment guidelines. In this paper, a hyperthermia treatment planning system (HTPS) is employed to investigate the effect of these guidelines on global power distribution, their effectiveness and the rationale behind each guideline. Materials and methods: Four guidelines were investigated. The first two prescribe steering actions for balancing intraluminal temperatures and alleviating complaints of deep-seated pain or pressure. The third guideline handles superficial complaints of pain or heat sensation. The last guideline states that frequency should be increased from 77 MHz upwards in case of multiple, opposite, painful regions uncontrollable by the previous steering actions. For all steering actions it is assumed that input power is increased until complaints occur. Sigma Hyperplan was used to calculate specific absorption rate (SAR) distributions for five patient models with locally advanced cervical cancer. Absorbed power ratios of different regions of interest were evaluated to illustrate steering efficacy and complaint reduction. Results and conclusions: Phase steering is effective in shifting the central power distribution to the periphery, and is an appropriate method to balance temperatures or to handle deep-seated complaints. Reduction of amplitude is the proper action to alleviate superficial complaints of heat or pressure. Compression of the SAR distribution, mainly in the lateral direction, is predicted with increasing frequency. Hence, for complaints in the lower back or on the sides, a frequency increase should be considered. We conclude that the results of the HTPS are in close agreement with the empirical steering guidelines.

Incidence of acute peripheral neurotoxicity after deep regional hyperthermia of the pelvis (Article)

2008-06-01T00:00:00Z

Background: After observing rather severe acute neurotoxicity in a few patients following deep hyperthermia treatment for a pelvic tumour, we evaluated the incidence of neurotoxicity in all patients treated with deep hyperthermia of the pelvis between June 1990 and April 2004. Materials and methods: Hyperthermia treatment registrations and hospital charts of all 736 patients were reviewed. Differences between the incidence of neurotoxicity in subgroups of patients were evaluated by 2×2 exact tests. Results: Grade 2 or 3 acute neurotoxicity occurred in 2.3% of patients, grade 3 in 0.7%. The duration of symptoms was longer than 3 months in 6 patients (0.8%). Neurological examination in 5 patients showed that the most commonly involved structures are the sacral and lower lumbar nerve roots and the sacral plexus. Acute neurotoxicity occurred only after November 1999 and only in patients treated for primary cervical cancer. Comparison of applied powers and achieved temperatures in patients developing neurotoxicity did not show differences between treatment sessions which resulted in neurotoxicity and sessions not resulting in neurotoxicity. Conclusion: Acute neurotoxicity following hyperthermia for pelvic tumours is a rare complication, but can result in symptoms affecting the activities of daily life. We found no patient, tumour or treatment characteristics predictive for a risk of neurotoxicity.

SAR characteristics of the Sigma-60-Ellipse applicator (Article)

2008-06-01T00:00:00Z

Purpose: To characterize the basic performance of the Sigma-60-Ellipse applicator. Materials and methods: The E-field distributions were measured using Schottky diode sheets in a cylindrical phantom (diameter 26 cm, length 50 cm), filled with saline-water (2 g NaCl/L). The phantom was positioned symmetrically in the Sigma-60-Ellipse applicator. The stability of the SAR distribution was assessed as a function of power and frequency. Furthermore, the accuracy of target steering was evaluated at various frequencies. Finally, the SAR characteristics were compared with those of the Sigma-60 and the Sigma-Eye applicators. Results: The average 50% iso-SAR area increased from 241 to 296 cm2when the RF power increased from 100 to 1600 W. The SAR maximum was located in the centre of the applicator for the frequencies of 75-80 MHz and it moves towards the feet for higher frequencies (up to 3.5 cm at 120 MHz). The average 50% iso-SAR area decreased from 268 to 161 cm2with increasing frequency from 75 to 120 MHz. The 50% iso-SAR longitudinal length was almost stable (mean 21.3 cm) at 75-120 MHz for both power outputs of 400 and 800 W. As expected the 50% iso-SAR radial length decreased with frequency from 14.9 cm at 75 MHz to 8.4 cm at 120 MHz. There was a fair agreement between requested and measured target settings. At the lower frequencies of 75-90 MHz and at 100 MHz the SAR characteristics were almost identical to those of the Sigma-60 and Sigma-Eye applicators, respectively. Conclusion: At the frequency rangeof 75-90 MHz the Sigma-60 and at 100 MHz the Sigma-Eye can safely replaced by the Sigma-60-Ellipse applicator.

Long-Term Improvement in Treatment Outcome After Radiotherapy and Hyperthermia in Locoregionally Advanced Cervix Cancer: An Update of the Dutch Deep Hyperthermia Trial (Article)

2008-03-15T00:00:00Z

Purpose: The local failure rate in patients with locoregionally advanced cervical cancer is 41-72% after radiotherapy (RT) alone, whereas local control is a prerequisite for cure. The Dutch Deep Hyperthermia Trial showed that combining RT with hyperthermia (HT) improved 3-year local control rates of 41-61%, as we reported earlier. In this study, we evaluate long-term results of the Dutch Deep Hyperthermia Trial after 12 years of follow-up. Methods and Materials: From 1990 to 1996, a total of 114 women with locoregionally advanced cervical carcinoma were randomly assigned to RT or RT + HT. The RT was applied to a median total dose of 68 Gy. The HT was given once weekly. The primary end point was local control. Secondary end points were overall survival and late toxicity. Results: At the 12-year follow-up, local control remained better in the RT + HT group (37% vs. 56%; p = 0.01). Survival was persistently better after 12 years: 20% (RT) and 37% (RT + HT; p = 0.03). World Health Organization (WHO) performance status was a significant prognostic factor for local control. The WHO performance status, International Federation of Gynaecology and Obstetrics (FIGO) stage, and tumor diameter were significant for survival. The benefit of HT remained significant after correction for these factors. European Organization for Research and Treatment of Cancer Grade 3 or higher radiation-induced late toxicities were similar in both groups. Conclusions: For locoregionally advanced cervical cancer, the addition of HT to RT resulted in long-term major improvement in local control and survival without increasing late toxicity. This combined treatment should be considered for patients who are unfit to receive chemotherapy. For other patients, the optimal treatment strategy is the subject of ongoing research.

RF-power and temperature data analysis of 444 patients with primary cervical cancer: Deep hyperthermia using the Sigma-60 applicator is reproducible (Article)

2007-12-01T00:00:00Z

Treatment reproducibility is important to guarantee reproducible treatment-outcome, a low-complication rate and efficient treatment procedures. This study evaluated the performance of loco-regional deep hyperthermia with four BSD-2000 configurations during 1990-2005 using the direct available parameters, i.e., temperature and power. Primary cervical cancer patients (n = 444) were all treated within the Sigma-60. Patients were grouped in three weight-groups: <61 kg, 61-70 kg, <70 kg. Different temperature and power indices were extensively analyzed per BSD configuration, per weight-group, and over the time-period. No substantial variations were found for temperature/power indices over the four BSD configurations or for the temperature doses in similar weight-groups. The 'bare' power indices were increased with weight; however, the derivative power-related (W/kg, W/cm2) and temperature indices decreased. Large variations were found in the power-related parameters during 1991-1996 (1st time-period), whereas they were much smaller during 1997-2005 (2nd time-period). The most relevant change noted was the adaptation of the treatment strategy with respect to power modulation. The average frequency of switched-off was 3.4 and 8.9 times/treatment session for the 1st and 2nd time-period, respectively, while the average duration of each switched-off time was 78.2 vs. 38.3 s. The yearly average of vagina T50 was in the range of 39.3-40.2°C (1st time-period) and 40.0-40.5°C (2nd time-period). In 40% of the patients, a positive correlation was found between normalized net integrated power per pelvic area and vagina T50. Good reproducible heating is achieved with the BSD-2000 Sigma-60 irrespective of the regular technological upgrades of the system and variation of trained staff-members.

A Patch Antenna Design for Application in a Phased-Array Head and Neck Hyperthermia Applicator (Article)

2007-11-01T00:00:00Z

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.

The HYPERcollar: A novel applicator for hyperthermia in the head and neck (Article)

2007-11-01T00:00:00Z

The purpose of this work was to define all features, and show the potential, of the novel HYPERcollar applicator system for hyperthermia treatments in the head and neck region. The HYPERcollar applicator consists of (1) an antenna ring, (2) a waterbolus system and (3) a positioning system. The specific absorption rate (SAR) profile of this applicator was investigated by performing infra-red measurements in a cylindrical phantom. Mandatory patient-specific treatment planning was performed as an object lesson to a patient with a laryngeal tumour and an artificial lymph node metastasis. Comfort tests with healthy volunteers have revealed that the applicator provides sufficient comfort to maintain in treatment position for an hour: the standard hyperthermia treatment duration in our centre. By phantom measurements, we established that a central focus in the neck can be obtained, with 50% iso-SAR lengths of 3.5 cm in transversal directions (x/y) and 9–11 cm in the axial direction (z). Using treatment planning by detailed electromagnetic simulations, we showed that the SAR pattern can be optimised to enable simultaneous encompassing of a primary laryngeal tumour and a lymph node metastasis at the 25% iso-SAR level. This study shows that the applicator enables a good control, and sufficient possibilities for optimisation, of the SAR pattern. In an ongoing clinical feasibility study, we will investigate the possibilities of heating various target regions in the neck with this apparatus.

Comparison of intratumor and intraluminal temperatures during locoregional deep hyperthermia of pelvic tumors (Article)

2007-09-01T00:00:00Z

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°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.

Benefits of superficial hyperthermia treatment planning: Five case studies (Article)

2007-08-01T00:00:00Z

Purpose: To demonstrate the benefits of treatment planning in superficial hyperthermia. Materials and methods: Five patient cases are presented, in which treatment planning was applied to troubleshoot treatment-limiting hotspots, to select the optimum applicator type and orientation, to assess the risk associated with metallic implants, to assess the feasibility of heating a deeper seated tumour, and to analyse the effective SAR coverage resulting from arrays of multiple incoherent applicators. FDTD simulation tools were used to investigate treatment options, either based on segmented or simplified anatomies. Results: The background, approach and model implementation are presented per case. SAR cross-sections, profiles and isosurfaces are visualized to predict the effective SAR coverage of the target and the location of the maximum power absorption. In addition, the followed treatment strategy and the implications for the clinical treatment are given: for example, higher temperatures, relief of treatment limiting hot-spots or increased power input. Conclusions: Treatment planning in superficial hyperthermia can be applied to improve clinical routine. Its application supports the selection of the optimum technique in non-standard cases, leading to direct benefits for the patient. In addition, treatment planning has shown to be an excellent tool for education and training for hyperthermia technicians and physicians.

A head and neck hyperthermia applicator: Theoretical antenna array design (Article)

2007-06-27T00:00:00Z

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 12.5 cm 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.

Electromagnetic Head-And-Neck Hyperthermia Applicator: Experimental Phantom Verification and FDTD Model (Article)

2007-06-01T00:00:00Z

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, Schottky-diode 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.

On heating head and neck tumours using the novel clinical em applicator: the HYPERcollar (Article)

2007-05-01T00:00:00Z

Abstract Purpose: Definition of all features and the potential of the novel HYPERcollar applicator system for hyperthermia treatments in the head and neck (H&N) region. Methods and Materials: The HYPERcollar applicator consists of 1) an antenna ring, 2) a waterbolus system and 3) a positioning system. The specific absorption rate (SAR) profile of this applicator is investigated by performing infra-red (IR) measurements in a cylindrical phantom. Mandatory patient-specific treatment planning is performed as an object lesson to a patient with a laryngeal tumour and an artificial lymph node metastasis. Results: The comfort tests with healthy volunteers have revealed that the applicator provides su±cient comfort to maintain in treatment position for an hour: in our center the standard hyperthermia treatment duration. We further established that a central focus in the neck can be obtained, with 50% iso-SAR lengths of 3.5cm in transversal directions and 9-11cm in the axial direction (z). Using treatment planning by detailed electromagnetic simulations, we showed that the SAR pattern can be optimized to enable simultaneous encompassing a primary laryngeal tumour and a lymph node metastasis at the 25% iso-SAR level. Conclusions: A site-specific H&N applicator was designed that enables good control and sufficient possibilities for optimizing the SAR pattern. In an ongoing clinical feasibility study we will investigate the possibilities of heating various target regions in the neck with this apparatus.

An Electromagnetic Head and Neck Hyperthermia Applicator: experimental phantom verification and FDTD model (Article)

2007-02-01T00:00:00Z

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 head and neck hyperthermia applicator: Theoretical antenna array design (Article)

2007-02-01T00:00:00Z

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.

Assessment of the local SAR Distortion by Major Anatomical Structures in a Cylindrical Neck Phantom (Article)

2005-03-01T00:00:00Z

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.

Theoretical Investigation of the Feasibility to Deposit RF Energy Centrally in the Head-and-Neck Region (Article)

2005-02-01T00:00:00Z

Purpose: To investigate the ability to deposit radiofrequency energy centrally in the neck as a function of antenna positions, number of antennas, and operating frequency. Methods and Materials: Power absorption (PA) distributions in a realistic model of the head-and-neck anatomy are calculated in which the head model is irradiated by an array of dipole antennas. The relative PA distributions corresponding to different setups are visualized and analyzed using the ratio of the average PA (aPA) in the target and neck region. Results: Both the PA distributions and aPA ratios indicate an optimal focusing ability of the setups (i.e., the ability to direct energy efficiently into the target region), between 400 and 600 MHz. In this frequency band, the focusing ability depends only moderately on the size of the neck. Finally, it is found that the focusing ability at 433 MHz is increased significantly by increasing the number of antenna elements. Conclusions: The optimal frequency is found to be highly dependent on the size of the target volume; thus, a single optimum is hard to define. However, future clinical research will focus on 433 MHz based on the optimal range of frequencies, as found in this study.