Radiofrequency applicator concepts for thermal magnetic resonance of brain tumors at 297 MHz (7.0 Tesla)

Abstract

Purpose: Thermal intervention is a potent sensitizer of cells to chemo-and radiotherapy in cancer treatment. Glioblastoma multiforme (GBM) is a potential clinical target, given the cancer's aggressive nature and resistance to current treatment options. The annular phased array (APA) technique employing electromagnetic waves in the radiofrequency (RF) range allows for localized temperature increase in deep seated target volumes (TVs). Reports on clinical applications of the APA technique in the brain are still missing. Ultrahigh field magnetic resonance (MR) employs higher frequencies than conventional MR and has potential to provide focal temperature manipulation, high resolution imaging and noninvasive temperature monitoring using an integrated RF applicator (ThermalMR). This work examines the applicability of RF applicator concepts for ThermalMR of brain tumors at 297 MHz (7.0 Tesla). Methods: Electromagnetic field (EMF) simulations are performed for clinically realistic data based on GBM patients. Two algorithms are used for specific RF energy absorption rate based thermal intervention planning for small and large TVs in the brain, aiming at maximum RF power deposition or RF power uniformity in the TV for 10 RF applicator designs. Results: For both TVs, the power optimization outperformed the uniformity optimization. The best results for the small TV are obtained for the 16 element interleaved RF applicator using an elliptical antenna arrangement with water bolus. The two row elliptical RF applicator yielded the best result for the large TV. Discussion: This work investigates the capacity of ThermalMR to achieve targeted thermal interventions in model systems resembling human brain tissue and brain tumors.

Patient-Specific Planning for Thermal Magnetic Resonance of Glioblastoma Multiforme

“…Deep RF induced hyperthermia of GBM presents an alternative direction. Recent developments have reported on RF hyperthermia of GBM using fixed frequencies (f = 297 MHz [ 15 , 16 ], f = 915 MHz [ 17 ]) or multiple frequencies [ 18 , 19 ]. Magnetic nanoparticle heating has also shown promising results as localized adjuvant therapy [ 20 , 21 ].…”

“…Taken together, this has stimulated the development of RF hardware including multi-channel signal generators and RF applicators tailored for HT of the brain [ 15 , 16 , 27 , 28 , 29 ]. Typical RF hyperthermia devices are annular-phased-arrays (APA) with the steer- ability of the RF field depending on the number of independent transmit channels [ 2 , 15 , 30 ].…”

“…Typical RF hyperthermia devices are annular-phased-arrays (APA) with the steer- ability of the RF field depending on the number of independent transmit channels [ 2 , 15 , 30 ]. Arranging the antennae in multiple rings in the cranial–caudal direction increases the focusing capabilities of the RF array [ 16 , 31 , 32 ]. Moreover, HT planning (HTP) procedures have been advanced using numerical approaches, including field shaping optimization algorithms [ 19 , 33 , 34 ].…”

“…A number of algorithms has been investigated, differing in constraints and targets used for optimization. Some algorithms target the global RF power deposition [ 33 ], optimize the dominant component of the electric (E-) field [ 34 ], use virtual observation points (VOPs) to accelerate the optimization [ 16 ], or compute an optimum fit to a given target RF power distribution using one or multiple RF frequencies [ 19 ]. These hardware and software developments are of relevance for brain tumor HT, where a rigorous confinement of high RF exposure levels to the target volume (TV) is essential.…”

Design, Implementation, Evaluation and Application of a 32-Channel Radio Frequency Signal Generator for Thermal Magnetic Resonance Based Anti-Cancer Treatment

“…Vigorous fundamental and (bio)engineering research into electromagnetic radiation has resulted in a large body of literature documenting technical advances in HT devices [ 9 ]. HT devices are increasingly capable of the personalized radio frequency (RF)-induced heating of target tissue volumes guided by sophisticated treatment planning procedures and thermal dose control [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. Thermal Magnetic Resonance (ThermalMR) is an HT variant that accommodates RF-induced heating [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ], temperature mapping using MR thermometry (MRT) [ 26 , 27 , 28 , 29 ], anatomic and functional imaging and the option for x-nuclei MR imaging (MRI) in a single, multi-purpose RF applicator.…”