SAR thresholds for electromagnetic exposure using functional thermal dose limits

\u3cp\u3eBACKGROUND AND PURPOSE: To protect against any potential adverse effects to human health from localised exposure to radio frequency (100 kHz-3 GHz) electromagnetic fields (RF EMF), international health organisations have defined basic restrictions on specific absorption rate (SAR) in tissues. These exposure restrictions incorporate safety factors which are generally conservative so that exposures that exceed the basic restrictions are not necessarily harmful. The magnitude of safety margin for various exposure scenarios is unknown. This shortcoming becomes more critical for medical applications where the safety guidelines are required to be relaxed. The purpose of this study was to quantify the magnitude of the safety factor included in the current basic restrictions for various exposure scenarios under localised exposure to RF EMF.\u3c/p\u3e\u3cp\u3eMATERIALS AND METHODS: For each exposure scenario, we used the lowest thermal dose (TD) required to induce acute local tissue damage reported in literature, calculated the corresponding TD-functional SAR limits (SARTDFL) and related these limits to the existing basic restrictions, thereby estimating the respective safety factor.\u3c/p\u3e\u3cp\u3eRESULTS: The margin of safety factor in the current basic restrictions on 10 g peak spatial average SAR (psSAR10g) for muscle is large and can reach up to 31.2.\u3c/p\u3e\u3cp\u3eCONCLUSIONS: Our analysis provides clear instructions for calculation of SARTDFL and consequently quantification of the incorporated safety factor in the current basic restrictions. This research can form the basis for further discussion on establishing the guidelines dedicated to a specific exposure scenario, i.e. exposure-specific SAR limits, rather than the current generic guidelines.\u3c/p\u3

Computational electromagnetic modeling is key in objective control of hyperthermia

\u3cp\u3eConfining treatment to the tumor to improve therapeutic outcome and reduce toxicity, is a hot issue in cancer research. Hyperthermia is recognized as a strong sensitizer for radiotherapy and chemotherapy enhancing tumor control without increasing toxicity. Today's electromagnetic hyperthermia systems heat large tissue volumes with limited ability to selectively heat the tumor. Fortunately, tremendous improvements in 3-dimensional electromagnetic & temperature modelling provide an exciting opportunity to design advanced multi-element electromagnetic applicator systems. Together with feedback control using MR non-invasive thermometry and smart E-field sensors, this paves the way for selective tumor heating and potentially prescription of a thermal dose.\u3c/p\u3

Hyperthermia treatment planning guided applicator selection for sub-superficial head and neck tumors heating

\u3cp\u3ePURPOSE: In this study, we investigated the differences in hyperthermia treatment (HT) quality between treatments applied with different hyperthermia systems for sub-superficial tumours in the head and neck (H&N) region.\u3c/p\u3e\u3cp\u3eMATERIALS AND METHODS: In 24 patients, with a clinical target volume (CTV) extending up to 6 cm from the surface, we retrospectively analysed the predicted HT quality achievable by two planar applicator arrays or one phased-array hyperthermia system. Hereto, we calculated and compared the specific absorption rate (SAR) and temperature distribution coverage of the CTV and gross tumour volume (GTV) for the Lucite cone applicator (LCA: planar), current sheet applicator (CSA: planar) and the HYPERcollar (phased-array).\u3c/p\u3e\u3cp\u3eRESULTS: The HYPERcollar provides better SAR coverage than planar applicators if the target region is fully enclosed by its applicator frame. For targets extending outside the HYPERcollar frame, sufficient SAR coverage (25% target coverage, i.e. TC25 ≥ 75%) can still be achieved using the LCA when the target is fully under the LCA aperture and not deeper than 50 mm from the patient surface.\u3c/p\u3e\u3cp\u3eCONCLUSION: Simulations predict that the HYPERcollar (hence also its successor the HYPERcollar3D) is to be preferred over planar applicators such as LCA and current sheet applicator in sub-superficial tumours in the H&N region when used within specifications.\u3c/p\u3

Waveguide-based applicators for superficial hyperthermia treatment:is tuning really required?

\u3cp\u3eWaveguide-based applicators are used for hyperthermia treatment of superficial tumors, e.g. chest wall recurrences. During superficial hyperthermia treatment (SHT), the patient is in the near field of these antennas, so its radiating properties may vary. To maximize the transfer power from generators towards treatment area, waveguide-based applicators usually feature means for tuning the applicators. The purpose of this study was to investigate whether waveguide-based applicators for SHT really require such tuning. Hereto, we designed and optimized a waveguide lucite applicator at 434 MHz, applying a muscle phantom and a layered (skin, fat and muscle) phantom to mimic the patient.Applicator performance was measured for different water bolus temperatures and temperatures of the water circulating the applicator by studying impedance matching. S\u3csub\u3e11\u3c/sub\u3e ≤ -15 dB was measured for nine locations at the skin of a volunteer and three different water bolus temperatures.We conclude that tuning of waveguidebased applicators is not required when the applicator is properly designed.\u3c/p\u3

A hyperthermia system and a method for generating a focused three-dimensional rf field

The invention relates to a hyperthermia system (30) for treating a patient, comprising an RF power unit, one or more RF antenna's connected to the RF power unit for generating a focused three-dimensional RF field, a controller (37) for adjusting the RF power source and/or the one or more RF antenna's for steering the focused three-dimensional RF field; a sensor for sensing a parameter (34) representative of the focused three-dimensional RF field; a communication environment (36) for inputting data from the said sensor and/or additional information provided by the patient, said communication environment being capable of generating trigger signals to the controller for in use steering the focused three-dimensional RF filed in real time. The invention further relates to a method for generation a focused three- dimensional RF field

Impact of segmentation detail in hyperthermia treatment planning:comparison between detailed and clinical tissue segmentation

\u3cp\u3eTreatment planning for deep pelvic hyperthermia is currently based on tissue models comprising four tissue categories. For head and neck hyperthermia, we earlier found that more tissues are required for an accurate representation. Hence, we studied the accuracy of the clinical tissue segmentation (4 tissues) using a full detailed tissue list segmentation (80 tissues) as benchmark. The SAR and temperature distributions were evaluated and relevant differences were found. Also, the large and unknown variation in blood perfusion results in a large uncertainty in the predicted temperature distributions. In summary, this study showed that the number of tissues segmented is relevant for both SAR and the temperature prediction accuracy.\u3c/p\u3

Hyperthermia and the need to monitor temperature

\u3cp\u3eExtensive biologic research has shown that adjuvant thermal therapy, i.e. heating tumors to 40-43°C, is a promising approach to increase the efficacy of existing radio- and chemotherapy protocols. The fact that in clinical trials, hyperthermia has shown not to increase toxicity is a major drive to invest in developing innovative devices and applicators to deliver thermal therapies. Moreover, the recent demonstrated ability of hyperthermia to decrease the repair of DNA double strand breaks provides a gateway to new treatments strategies involving hyperthermia and in combination with temperature sensitive drug carriers hyperthermia can be used for triggered local drug delivery.\u3c/p\u3

Recent advances in EM cancer treatments

\u3cp\u3eBoth a novel hyperthermia treatment planning tool and a new head&neck applicator have been developed to overcome limitations of existing approaches. The treatment planning tool is optimized for high quality, accurate, realistic simulations of highly detailed models. The applicator offers superior steerability and online control.\u3c/p\u3

Hyperthermia by electromagnetic fields to enhanced clinical results in oncology

\u3cp\u3eConfining treatment to the tumor to improve therapeutic outcome and reduce toxicity, is a hot issue in cancer research. Hyperthermia is recognized as a strong sensitizer for radiotherapy and chemotherapy enhancing tumor control without increasing toxicity. Today's electromagnetic hyperthermia systems heat large tissue volumes with limited ability to selectively heat the tumor. Fortunately, tremendous improvements in 3-dimensional electromagnetic & temperature modelling provide an exciting opportunity to design advanced multi-element electromagnetic applicator systems. Together with feedback control using MR non-invasive thermometry and smart E-field sensors, this paves the way for selective tumor heating and potentially prescription of a thermal dose. A technological advanced hyperthermia system, with guaranteed delivery of high quality hyperthermia lowers the threshold for newcomers to apply hyperthermia. Combined with recent proof that hyperthermia blocks DNA repair and new, exciting, ways for controlled drug delivery using temperature sensitive liposome encapsulated drugs, this is expected to increase interest of the medical community in hyperthermia.\u3c/p\u3

Latest advances in EM hyperthermia cancer treatments

\u3cp\u3eInvestigations have been carried out to determine the limitations of currently used technology in the field of hyperthermia cancer treatment. A novel hyperthermia treatment planning tool and a new head&neck applicator have been developed. The treatment planning tool is optimized for high quality, accurate, realistic simulations of highly detailed models. The applicator offers superior steerability and online control.\u3c/p\u3