Magnetic resonance-guided high-intensity focused ultrasound combined with radiotherapy for palliation of head and neck cancer-a pilot study

A review of high-intensity focused ultrasound as a novel and non-invasive interventional radiology technique

High-intensity focused ultrasound (HIFU) is a non-invasive interventional radiology technology, which has been generally accepted in clinical practice for the treatment of benign and malignant tumors. HIFU can cause targeted tissue coagulative necrosis and protein denaturation by thermal or non-thermal effects, guided by diagnostic ultrasound or magnetic resonance imaging, without destruction of the normal adjacent tissue, under sedation or general anesthesia. HIFU has become an important alternative to standard treatments of solid tumors, including surgery, radiation, and medications. The aim of this review is to describe the development, principle, devices, and clinical applications of HIFU.

Sonication strategies toward volumetric ultrasound hyperthermia treatment using the ExAblate body MRgFUS system

PURPOSE

The ExAblate body MRgFUS system requires advanced beamforming strategies for volumetric hyperthermia. This study aims to develop and evaluate electronic beam steering, multi-focal patterns, and sector vortex beamforming approaches in conjunction with partial array activation using an acoustic and biothermal simulation framework along with phantom experiments.

METHODS

The simulation framework was developed to calculate the 3D acoustic intensity and temperature distribution resulting from various beamforming and scanning strategies. A treatment cell electronically sweeping a single focus was implemented and evaluated in phantom experiments. The acoustic and thermal focal size of vortex beam propagation was quantified according to the vortex modes, number of active array elements, and focal depth.

RESULTS

Turning off a percentage of the outer array to increase the f-number increased the focal size with a decrease in focal gain. 60% active elements allowed generating a sonication cell with an off-axis of 10 mm. The vortex mode number 4 with 60% active elements resulted in a larger heating volume than using the full array. Volumetric hyperthermia in the phantom was evaluated with the vortex mode 4 and respectively performed with 100% and 80% active elements. MR thermometry demonstrated that the volumes were found to be 18.8 and 29.7 cm³, respectively, with 80% array activation producing 1.58 times larger volume than the full array.

CONCLUSIONS

This study demonstrated that both electronic beam steering and sector vortex beamforming approaches in conjunction with partial array activation could generate large volume heating for HT delivery using the ExAblate body array.

Combining Low-Dose Radiation Therapy and Magnetic Resonance Guided Focused Ultrasound to Reduce Amyloid-β Deposition in Alzheimer's Disease

Amyloid-β deposition is one of the neuropathological hallmarks of Alzheimer's disease (AD), but pharmacological strategies toward its reduction are poorly effective.Preclinical studies indicate that low-dose radiation therapy (LD-RT) may reduce brain amyloid-β. Animal models and proof-of-concept preliminary data in humans have shown that magnetic resonance guided focused ultrasound (MRgFUS) can reversibly open the blood-brain-barrier and facilitate the delivery of targeted therapeutics to the hippocampus, to reduce amyloid-β and promote neurogenesis in AD. Ongoing clinical trials on AD are exploring whole-brain LD-RT, which may damage radio-sensitive structures, i.e., hippocampus and white matter, thus contributing to reduced neurogenesis and radiation-induced cognitive decline. However, selective irradiation of cortical amyloid-β plaques through advanced LD-RT techniques might spare the hippocampus and white matter. We propose combined use of advanced LD-RT and targeted drug delivery through MRgFUS for future clinical trials to reduce amyloid-β deposition in AD since its preclinical stages.

Boron Chemistry for Medical Applications

Boron compounds now have many applications in a number of fields, including Medicinal Chemistry. Although the uses of boron compounds in pharmacological science have been recognized several decades ago, surprisingly few are found in pharmaceutical drugs. The boron-containing compounds epitomize a new class for medicinal chemists to use in their drug designs. Carboranes are a class of organometallic compounds containing carbon (C), boron (B), and hydrogen (H) and are the most widely studied boron compounds in medicinal chemistry. Additionally, other boron-based compounds are of great interest, such as dodecaborate anions, metallacarboranes and metallaboranes. The boron neutron capture therapy (BNCT) has been utilized for cancer treatment from last decade, where chemotherapy and radiation have their own shortcomings. However, the improvement in the already existing (BPA and/or BSH) localized delivery agents or new tumor-targeted compounds are required before realizing the full clinical potential of BNCT. The work outlined in this short review addresses the advancements in boron containing compounds. Here, we have focused on the possible clinical implications of the new and improved boron-based biologically active compounds for BNCT that are reported to have in vivo and/or in vitro efficacy.

Boron neutron capture therapy at the crossroads - Where do we go from here?

As elegant as is the concept upon which Boron Neutron Capture Therapy (BNCT) is based, unfortunately it has not gained widespread acceptance by the physicians who are treating cancer patients on a daily basis. The question is why? Very simply put, the clinical results obtained in treating patients with high grade gliomas and recurrent tumors of the head and neck region have not been convincing enough to produce more interest in BNCT as a cancer treatment modality. There are a variety of reasons for this, one of the most important of which has been its dependency on nuclear reactors as neutron sources. With the advent of accelerator based neutron sources (ABNS), this hopefully will be addressed. If the results obtained from ongoing and soon to be initiated clinical trials can at least demonstrate equivalency to those obtained with nuclear reactors, this should address the first problem. The second problem relates to boron delivery agents, and despite the considerable efforts of chemists and biologists over the past 50 years, there are only two drugs that currently are being used clinically, sodium borocaptate (BSH) and boronophenylalanine (BPA). It is widely recognized that these two drugs are less than ideal. Perhaps new and more effective boron delivery agents will finally appear on the scene, but barring that, we will address the question of what can be done now to make BNCT a more effective cancer treatment modality.

Microbubble-assisted MRI-guided focused ultrasound for hyperthermia at reduced power levels

PURPOSE

Ultrasound contrast agent microbubbles were combined with magnetic resonance imaging (MRI)-guided focused ultrasound (MRgFUS) as a means to achieve mild hyperthermia at reduced power levels.

METHODS

MRgFUS hyperthermia (42°C for 20 min) was evaluated in rabbit thigh muscle or Vx2 tumors using infusions of microbubbles (Definity, 20 µL/kg) or saline (sham) administered over 5 min. The impact of treatments on drug uptake was assessed with liposomal doxorubicin (Caelyx, 2.5 mg/kg). Applied power levels before and after the injection of microbubbles or saline were compared, and drug uptake was evaluated with fluorometry of tissues harvested 24 hr post-treatment.

RESULTS

MRgFUS hyperthermia in muscle and tumors resulted in accurate temperature control (mean =42.0°C, root mean square error (RMSE) = 0.3°C). The power dropped significantly following the injection of microbubbles in muscle and tumors compared to exposures without microbubbles (-21.9% ± 12.5% vs -5.9% ± 7.8%, p = .009 in muscle; -33.8% ± 9.9% vs -3.0% ± 7.2%, p < .001 in tumors). Cavitation monitoring indicated emission of subharmonic, ultraharmonic, and elevated levels of fourth to sixth harmonic frequencies following microbubble injection. The drug delivery was elevated significantly in muscle with the use of microbubble-assisted relative to conventional heating (0.5 ± 0.5 ng/mg vs 0.20 ± 0.04 ng/mg, p = .05), whereas in tumors similar levels were found (11 ± 3 ng/mg vs 16 ± 4 ng/mg, p = .13).

CONCLUSIONS

The finding that microbubbles reduce the applied power requirements for hyperthermia has considerable clinical implications. The elevated levels of drug found in muscle but not tumor tissue suggest a complex interplay between the heating effects of microbubbles with those of enhanced permeabilization and possible vascular damage.

A realistic appraisal of boron neutron capture therapy as a cancer treatment modality

Boron neutron capture therapy (BNCT) is a binary therapeutic modality based on the nuclear capture and fission reactions that occur when the stable isotope boron-10 is irradiated with neutrons to produce high-energy alpha particles and recoiling lithium-7 nuclei. In this Commentary we will focus on a number of papers that were presented at a Symposium entitled "Current Clinical Status of Boron Neutron Capture Therapy and Paths to the Future", which was held in September 2017 at the China National Convention Center in Beijing. Results were presented by clinicians from Japan, Finland, the United States, the China mainland and Taiwan, China who have been working in the multiple disciplines that are required for carrying out clinical BNCT. The main focus was on the treatment of patients with malignant brain tumors, recurrent tumors of the head and neck region, and cutaneous melanomas. The results obtained in treating these patients were reported in detail and, although most of the patients with brain tumors and head and neck cancer were not cured, there was evidence of some clinical efficacy. Although there are a number of problems that must be addressed, further clinical studies to evaluate the efficacy of BNCT are warranted. First, despite considerable effort by numerous investigators over the past 40 years, there still are only two boron-containing drugs in clinical use, L-boronophenylalanine (BPA) and sodium borocaptate (BSH). Therefore, until new and more effective boron delivery agents are developed, efforts should be directed to improving the dosing and delivery of BPA and BSH. Second, due to a variety of reasons, nuclear reactor-based BNCT has ended except for its use in the China mainland and Taiwan. Therefore, the future of BNCT depends upon the results of the ongoing Phase II clinical trials that are being carried out in Japan and the soon to be initiated trials that will be carried out in Finland. If the results obtained from these clinical trials are sufficiently promising, then BNCT will have a clear path to the future, especially for patients with the therapeutically challenging malignancies that in the past have been treated with reactor-based BNCT.

Effect of Tempol on the prevention of irradiation-induced mucositis in miniature pigs

OBJECTIVE

The goals of this study were to (i) establish a useful miniature pig (minipig) model for irradiation-induced oral mucositis and (ii) evaluate the effect of Tempol to prevent its development.

METHODS AND MATERIALS

Minipigs were irradiated with 6 Gy for five consecutive days targeting the entire oral cavity. To prevent radiation damage, minipigs were treated with 30 mg kg^-1 Tempol 10 min before irradiation (n = 4), while the radiation-alone group was similarly injected with saline (n = 4). Lesions were graded using an oral mucositis score and visual inspection every 3 days, and biopsy of multiple sites was performed at day 18. Weight and chest and abdominal circumferences were measured every 3 days.

RESULTS

Lesions began about 12 days after the first irradiation fraction and healed about 30 days after irradiation. Epithelial thickness was calculated on the lingual and buccal mucosa on the 18th day after the first irradiation fraction. Tempol provided modest protection from ulceration after irradiation using this treatment strategy.

CONCLUSIONS

This study established a useful large animal model for irradiation-induced oral mucositis and showed modest beneficial effects of Tempol in limiting tissue damage. The latter finding may be potentially valuable in preventing oral mucositis in patients receiving irradiation for head and neck cancers.