Radionecrosis and cellular changes in small volume stereotactic brain radiosurgery in a porcine model

Ex vivo brain MRI to assess conventional and FLASH brain irradiation effects

BACKGROUND AND PURPOSE

The FLASH effect expands the therapeutic ratio of tumor control to normal tissue toxicity observed after delivery of ultra-high (>100 Gy/s FLASH-RT) vs. conventional dose rate radiation (CONV-RT). In this first exploratory study, we assessed whether ex-vivo Magnetic Resonance Imaging (MRI) could reveal long-term differences after FLASH-RT and CONV-RT whole-brain irradiation.

MATERIALS AND METHODS

Female C57BL/6 mice were divided into three groups: control (non-irradiated), conventional (CONV-RT 0.1 Gy/s), and ultra-high dose rates (FLASH-RT 1 pulse, 5.5 x 10^6 Gy/s), and received 10 Gy of whole-brain irradiation in a single fraction at 10 weeks of age. Mice were evaluated by Novel Object Recognition cognitive testing at 10 months post-irradiation and were sampled at 13 months post-irradiation. Ex-vivo brains were imaged with a 14.1 Tesla/26 cm magnet with a multimodal MRI protocol, including T2-weighted TurboRare (T2W) and diffusion-weighted imaging (DWI) sequences.

RESULTS

In accordance with previous results, cognitive tests indicated that animals receiving CONV-RT exhibited a decline in cognitive function, while FLASH-RT performed similarly to the controls. Ex-vivo MRI showed decreased hippocampal mean intensity in the CONV-RT mice compared to controls but not in the FLASH-RT group. Comparing CONV-RT to control, we found significant changes in multiple whole-brain diffusion metrics, including the mean Apparent Diffusion Coefficient (ADC) and Mean Apparent Propagator (MAP) metrics. By contrast, no significant diffusion changes were found between the FLASH-RT and control groups. In an exploratory analysis, compared to controls, regional diffusion metrics were primarily altered in the basal forebrain and the insular cortex after conventional radiation therapy (CONV-RT), and to a lesser extent after flash radiation therapy (FLASH-RT).

CONCLUSION

This study presents initial evidence that ex-vivo MRI uncovered changes in the brain after CONV-RT but not after FLASH-RT. The study indicates the potential use of ex vivo MRI to analyze the brain radiation responses at different dose rates.

Differentiating unirradiated mice from those exposed to conventional or FLASH radiotherapy using MRI

Background and purpose

The FLASH effect expands the therapeutic ratio of tumor control to normal tissue toxicity observed after delivery of ultra-high (>100 Gy/s FLASH-RT) vs. conventional dose rate radiation (CONV-RT). In this first exploratory study, we assessed whether ex-vivo Magnetic Resonance Imaging (MRI) could reveal long-term differences after FLASH-RT and CONV-RT whole-brain irradiation.

Materials and methods

Female C57BL/6 mice were divided into three groups: control (non-irradiated), conventional (CONV-RT 0.1 Gy/s), and ultra-high dose rates (FLASH-RT 1 pulse, 5.5 × 10^6 Gy/s), and received 10 Gy of whole-brain irradiation in a single fraction at 10 weeks of age. Mice were evaluated by Novel Object Recognition cognitive testing at 10 months post-irradiation and were sampled at 13 months post-irradiation. Ex-vivo brains were imaged with a 14.1 Tesla/26 cm magnet with a multimodal MRI protocol, including T2-weighted TurboRare (T2W) and diffusion-weighted imaging (DWI) sequences.

Results

In accordance with previous results, cognitive tests indicated that animals receiving CONV-RT exhibited a decline in cognitive function, while FLASH-RT performed similarly to the controls. MRI showed decreased hippocampal mean intensity in the CONV-RT mice compared to controls but not in the FLASH-RT group. Comparing CONV-RT to control, we found significant changes in multiple whole-brain diffusion metrics, including the mean Apparent Diffusion Coefficient (ADC) and Mean Apparent Propagator (MAP) metrics. By contrast, no significant diffusion changes were found between the FLASH-RT and control groups. In an exploratory analysis compared to controls, regional diffusion metrics were primarily altered in the basal forebrain and the insular cortex after CONV-RT, and after FLASH-RT, a trend reduction was also observed.

Conclusion

This study presents initial evidence that MRI can uncover clear changes in the brain after CONV-RT but not after FLASH-RT. The MRI results aligned with the observed cognitive protection after FLASH-RT, indicating the potential use of MRI to analyze the FLASH response.

High incidence of radiation-induced brain necrosis in the periventricular deep white matter: stereotactic radiotherapy for brain metastases using volumetric modulated arc therapy

PURPOSE

In this retrospective study, we aimed to evaluate the efficacy and incidence of radiation-induced brain necrosis (RBN) after volumetric modulated arc therapy-based stereotactic irradiation (VMAT-STI) for brain metastases.

METHODS

In the 220 brain metastatic lesions included between January 2020 and June 2022, there were 1-9 concurrently treated lesions (median 1). A biologically effective dose (BED)10 of 80 Gy and a reduced BED10 of 50 Gy were prescribed to the gross tumor volume (GTV) and planning target volume (PTV) (PTV = GTV + 3 mm) margins, respectively. The number of fractions was adjusted from 3 to 15 to accommodate different GTV sizes; for larger tumor volumes, this was increased while maintaining the BED10 values comparable to those for GTV and PTV margins.

RESULTS

Of the total patients, 16 (7%) exhibited locally progressive lesions; local tumor recurrence was observed in 2 (1%) patients, while RBN was noted in 14 (6%) patients. RBN was significantly more prevalent in the deep white matter around the lateral ventricles (DWM-LV) than in other sites, occurring in 9/22 (41%) lesions of metastases in the DWM-LV. The 2-year actuarial incidence risk of developing RBN was significantly higher in the DWM-LV (69%) than at other sites (5%).

CONCLUSION

The recurrence rate of brain metastases was low, and the incidence of RBN was lower in tumor sites other than the DWM-LV. However, the frequency of RBN was significantly higher in the DWM-LV region. Additional VMAT-STI-prescribed dose protocols are necessary to reduce RBN incidence in DWM-LVs.

Anatomy and connectivity of the Göttingen minipig subgenual cortex (Brodmann area 25 homologue)

BACKGROUND

The subgenual gyrus is a promising target for deep brain stimulation (DBS) against depression. However, to optimize this treatment modality, we need translational animal models.

AIM

To describe the anatomy and connectivity of the Göttingen minipig subgenual area (sgC).

MATERIALS AND METHODS

The frontal pole of 5 minipigs was cryosectioned into 40 μm coronal and horizontal sections and stained with Nissl and NeuN-immunohistochemistry to visualize cytoarchitecture and cortical lamination. Eight animals were unilaterally stereotaxically injected in the sgC with anterograde (BDA) and retrograde (FluoroGold) tracers to reveal the sgC connectivity.

RESULTS

In homology with human nomenclature (Brodmann 1909), the minipig sgC can be subdivided into three distinct areas named area 25 (BA25), area 33 (BA33), and indusium griseum (IG). BA25 is a thin agranular cortex, approximately 1 mm thick. Characteristically, perpendicular to the pial surface, cell-poor cortical columns separate the otherwise cell-rich cortex of layer II, III and V. In layer V the cells are of similar size as seen in layer III, while layer VI contains more widely dispersed neurons. BA33 is less differentiated than BA25. Accordingly, the cortex is thinner and displays a complete lack of laminar differentiation due to diffusely arranged small, lightly stained neurons. It abuts the IG, which is a neuron-dense band of heavily stained small neurons separating BA33 directly from the corpus callosum and the posteriorly located septal nuclear area. Due to the limited area size and nearby location to the lateral ventricle and longitudinal cerebral fissure, only 3/8 animals received sgC injections with an antero- and retrograde tracer mixture. Retrograde tracing was seen primarily to the neighbouring ipsilateral ventral- and mPFC areas with some contralateral labelling as well. Prominent projections were furthermore observed from the ipsilateral insula, the medial aspect of the amygdala and the hippocampal formation, diencephalon and the brainstem ventral tegmental area. Anterograde tracing revealed prominent projections to the neighbouring medial prefrontal, mPFC and cingulate cortex, while moderate staining was noted in the hippocampus and adjoining piriform cortex.

CONCLUSION

The minipig sgC displays a cytoarchitectonic pattern and connectivity like the human and may be well suited for further translational studies on BA25-DBS against depression.

Determinants of cerebral radionecrosis in animal models: A systematic review

BACKGROUND

Radionecrosis is a common complication in radiation oncology, while mechanisms and risk factors have yet to be fully explored. We therefore conducted a systematic review to understand the pathogenesis and identify factors that significantly affect the development.

METHODS

We performed a systematic literature search based on the PRISMA guidelines using PubMed, Ovid, and Web of Science databases. The complete search strategy can be found as a preregistered protocol on PROSPERO (CRD42023361662).

RESULTS

We included 83 studies, most involving healthy animals (n = 72, 86.75 %). High doses of hemispherical irradiation of 30 Gy in rats and 50 Gy in mice led repeatedly to radionecrosis among different studies and set-ups. Higher dose and larger irradiated volume were associated with earlier onset. Fractionated schedules showed limited effectiveness in the prevention of radionecrosis. Distinct anatomical brain structures respond to irradiation in various ways. White matter appears to be more vulnerable than gray matter. Younger age, more evolved animal species, and genetic background were also significant factors, whereas sex was irrelevant. Only 13.25 % of the studies were performed on primary brain tumor bearing animals, no studies on brain metastases are currently available.

CONCLUSION

This systematic review identified various factors that significantly affect the induction of radionecrosis. The current state of research neglects the utilization of animal models of brain tumors, even though patients with brain malignancies constitute the largest group receiving brain irradiation. This latter aspect should be primarily addressed when developing an experimental radionecrosis model for translational implementation.

A high-density multi-electrode platform examining the effects of radiation on in vitro cortical networks

Radiation therapy and stereotactic radiosurgery are common treatments for brain malignancies. However, the impact of radiation on underlying neuronal circuits is poorly understood. In the prefrontal cortex (PFC), neurons communicate via action potentials that control cognitive processes, thus it is important to understand the impact of radiation on these circuits. Here we present a novel protocol to investigate the effect of radiation on the activity and survival of PFC networks in vitro. Escalating doses of radiation were applied to PFC slices using a robotic radiosurgery platform at a standard dose rate of 10 Gy/min. High-density multielectrode array recordings of radiated slices were collected to capture extracellular activity across 4,096 channels. Radiated slices showed an increase in firing rate, functional connectivity, and complexity. Graph-theoretic measures of functional connectivity were altered following radiation. These results were compared to pharmacologically induced epileptic slices where neural complexity was markedly elevated, and functional connections were strong but remained spatially focused. Finally, propidium iodide staining revealed a dose-dependent effect of radiation on apoptosis. These findings provide a novel assay to investigate the impacts of clinically relevant doses of radiation on brain circuits and highlight the acute effects of escalating radiation doses on PFC neurons.

A 72-h sedated porcine model of traumatic spinal cord injury

Introduction

There is an increasing focus on the prevention of secondary injuries following traumatic spinal cord injury (TSCI), especially through improvement of spinal cord perfusion and immunological modulation. Such therapeutic strategies require translational and controlled animal models of disease progression of the acute phases of human TSCI.

Research question

Is it possible to establish a 72-h sedated porcine model of incomplete thoracic TSCI, enabling controlled use of continuous, invasive, and non-invasive modalities during the entire sub-acute phase of TSCI?

Material and methods

A sham-controlled trial was conducted to establish the model, and 10 animals were assigned to either sham or TSCI. All animals underwent a laminectomy, and animals in the TSCI group were subjected to a weight-drop injury. Animals were then kept sedated for 72 h. The amount of injury was assessed by ex-vivo measures MRI-based fiber tractography, histology and immunohistochemistry.

Results

In all animals, we were successful in maintaining sedation for 72 h without comprising vital physiological parameters. The MRI-based fiber tractography showed that all TSCI animals revealed a break in the integrity of spinal neurons, whereas histology demonstrated no transversal sections of the spine with complete injury. Notably, some animals displayed signs of secondary ischemic tissue in the cranial and caudal sections.

Discussion and conclusions

This study succeeded in producing a porcine model of incomplete TSCI, which was physiologically stable up to 72 h. We believe that this TSCI model will constitute a potential translational model to study the pathophysiology secondary to TSCI in humans.

Dual-Target Radiosurgery for Concomitant Continuous Pain Presentation of Trigeminal Neuralgia: Radiomodulation Effect and Dose

OBJECTIVES

Patients with trigeminal neuralgia (TN) experience concomitant continuous pain (CCP) that can be difficult to treat. A dual-target approach delivering a high dose of radiation to the nerve and the contralateral thalamus can develop a fast radiomodulation effect on lowering pain. We sought to determine if this effect was dose dependent.

METHODS

We retrospectively reviewed 21 patients treated with radiosurgery in CCP and severe TN pain, with a visual analog scale (VAS) score of nine out of 10 at the time of treatment. Ten patients were treated with a high dose (>120 Gy) in the thalamus 90 Gy to the nerve, and the rest with a low dose (<120 Gy) to the thalamus and >90 Gy to the nerve.

RESULTS

Of those who received the high dose to the thalamus, six patients (60%) received 140 Gy, and four (40%) received 120 Gy, with a median dose to the trigeminal nerve of 90 and 85 Gy, respectively. The high thalamus dose showed a radiomodulation effect from day 1. The low thalamus dose did not produce radiomodulation on any of the first four days. The percentage of VAS score reduction one month after treatment was higher in the high-thalamus dose group than in the low-thalamus dose group. At three months, VAS score was 2 in the high-dose group and 4 in the low-dose group.

CONCLUSIONS

The radiomodulation effect in pain and dual-target radiosurgery is dose dependent in CCP in TN; a high dose can provide a more consistent clinical result than a lower dose.

Radiomodulation in Mixed, Complex Cancer Pain by Triple Target Irradiation in the Brain: A Preliminary Experience

Introduction

Up to 30% of terminally ill cancer patients experiencing intense pain might be refractory to opioid treatment. Complex cancer pain can be a mixture of somatic, visceral, and neuropathic pain with few or no effective alternatives to ameliorate pain. Radiosurgery to treat refractory pain in cancer has been reported with different degrees of success. Radiomodulation in pain could be defined as a fast (<72 h), substantial (>50%) pain relief by focal irradiation to a peripheric, and/or central mediated pain circuitry. Based on our previous experience, mixed, refractory cancer pain is usually unresponsive to single target irradiation of the hypophysis. We treated three patients using a multi-target approach.

Methods

Three terminally ill oncological patients experiencing refractory, complex, mixed pain from bone, abdomen, thorax, and brachial plexus were treated with triple target irradiation which consisted of irradiating with a maximum dose (Dmax) of 90 Gy to the hypophysis using either an 8 mm collimator with gamma ray (Infini) (Shenzhen, China: Masep Medical Company) or a 7.5 circular collimator with Cyberknife (Sunnyvale, CA: Accuray Inc.), the other two targets were the mesial structures of the thalamus bilaterally using a 4 mm collimator with Infini and the 5 mm circular collimator with CK delivering 90 Gy Dmax to each region. Patients had a VAS of 10 despite the best medical treatment.

A correlation was made between the 45 Gy and 20 Gy isodose curves of the two different technologies to the Morel stereotactic atlas of the thalamus and basal ganglia for further understanding of dose distribution reconstructions in accordance with the São Paulo-Würzburg atlas of the Human Brain Project were performed. Lastly, a scoping review of the literature regarding radiosurgery for oncological pain was performed.

Results

Radiomodulation effect was achieved in all patients; case 1 had a VAS of five at 72 h, three at 15 days, and three at the time of death (21 days after treatment). Case 2 had a VAS of six at 72 h, five at 15 days, and four at the time of death (29 days after treatment). Case 3 had a VAS of five at 72 h, six at 15 days, and six at the time of death (30 days). Morphine rescues for cases 1 and 2 were reduced to 84%, and 70% for case 3. Overall, there were no adverse effects to treatment although excessive sleepiness was reported by one patient. After reading the title and abstract, only 14 studies remained eligible for full-text evaluation, and only nine studies met inclusion criteria after full-text reading. For most reports (seven), the target was the hypophysis and in two reports, the target was the thalamus either with single or bilateral irradiation.

Conclusions

In complex, for refractory oncological pain of mixed nature (nociceptive, neuropathic, and visceral), very few, if any, treatment alternatives are currently available. We provide a small proof of concept that multitarget intracranial radiosurgery might be effective in ameliorating pain in this population. The doses administered per target are the lowest that have shown effectiveness thus far, a different strategy might be needed as opposed to single target “large” dose approach that has been tried in the past for complex mixed refractory oncological pain. By no means, in our experience, these treatments traduce in elimination of pain, clinical results might make pain to be more bearable and respond better to pain medication.

Non-ablative doses of focal ionizing radiation alters function of central neural circuits

BACKGROUND

Modulation of pathological neural circuit activity in the brain with a minimum of complications is an area of intense interest.

OBJECTIVE

The goal of the study was to alter neurons' physiological states without apparent damage of cellular integrity using stereotactic radiosurgery (SRS).

METHODS

We treated a 7.5 mm-diameter target on the visual cortex of Göttingen minipigs with doses of 40, 60, 80, and 100 Gy. Six months post-irradiation, the pigs were implanted with a 9 mm-wide, eight-shank multi-electrode probe, which spanned the radiation focus as well as the low-exposure neighboring areas.

RESULTS

Doses of 40 Gy led to an increase of spontaneous firing rate, six months post-irradiation, while doses of 60 Gy and greater were associated with a decrease. Subjecting the animals to visual stimuli resulted in typical visual evoked potentials (VEP). At 40 Gy, a significant reduction of the P1 peak time, indicative of higher network excitability was observed. At 80 Gy, P1 peak time was not affected, while a minor reduction at 60 Gy was seen. No distance-dependent effects on spontaneous firing rate, or on VEP were observed. Post-mortem histology revealed no evidence of necrosis at doses below 60 Gy. In an in vitro assay comprising of iPS-derived human neuron-astrocyte co-cultures, we found a higher vulnerability of inhibitory neurons than excitatory neurons with respect to radiation, which might provide the cellular mechanism of the disinhibitory effect observed in vivo.

CONCLUSION

We provide initial evidence for a rather circuit-wide, long-lasting disinhibitory effect of low sub-ablative doses of SRS.

Radiobiology

New understandings of the biology of radiosurgery are considered. Differences from the radiobiology of fractionated radiotherapy are outlined. It is noted DNA damage alone is insufficient to account for the tissue changes which occur. Changes in blood vessels and immunological mechanisms are also involved. Tissue repair is more rapid than previously thought so that dose rate (the rate of delivery of radiation to the tissues) has been seen to be more important. The value of fractionation is examined. The effect of radiosurgery on normal brain (so called functional radiosurgery) is considered. The desired effects may be achieved by a focal stable destruction of brain from a high radiation dose. They may also be achieved using a lower dose which acts through the mechanism known as radiosurgical neuromodulation.

The Impact of Volume Factor on the Long-Term Outcome of Gamma Knife Radiosurgery for Sporadic Cerebral Cavernous Malformations

OBJECTIVE

We aimed to evaluate the long-term outcome of gamma knife radiosurgery (GKRS) for the treatment of sporadic cerebral cavernous malformation (CCM), especially the influence of lesion volume on annual hemorrhage rate (AHR) of patients with CCM after GKRS.

METHODS

Fifty-one single-lesion patients with a history of hemorrhage who underwent radiosurgery at our institution were included and divided into 2 groups (A and B), based on their lesion volume. Group A included 25 patients with lesion volumes >1 cm³, whereas group B included 26 patients with lesion volumes ≤1 cm³. The clinical data of the patients were retrospectively analyzed.

RESULTS

All patients were followed up for more than 4 years after GKRS. The calculated AHR before GKRS was 18.49% in group A and 10.16% in group B. The calculated AHR after GKRS was 5.43% and 0.99% for groups A and B, respectively. Significant differences in AHR after GKRS were identified between group A and group B (P = 0.011). Thirty-seven patients with sporadic CCM (14 in group A, 23 in group B) experienced symptom improvement, and significant differences in symptom improvement were observed between group A and group B (P = 0.009).

CONCLUSIONS

GKRS decreased the risk of hemorrhage and was beneficial for symptomatic improvement in patients with sporadic CCM with a history of hemorrhage. The long-term clinical outcomes for patients with sporadic CCM with small lesion volumes (≤1 cm³) were better than those of patients with sporadic CCM with large lesion volumes (>1 cm³).

An Intracortical Implantable Brain-Computer Interface for Telemetric Real-Time Recording and Manipulation of Neuronal Circuits for Closed-Loop Intervention

Recording and manipulating neuronal ensemble activity is a key requirement in advanced neuromodulatory and behavior studies. Devices capable of both recording and manipulating neuronal activity brain-computer interfaces (BCIs) should ideally operate un-tethered and allow chronic longitudinal manipulations in the freely moving animal. In this study, we designed a new intracortical BCI feasible of telemetric recording and stimulating local gray and white matter of visual neural circuit after irradiation exposure. To increase the translational reliance, we put forward a Göttingen minipig model. The animal was stereotactically irradiated at the level of the visual cortex upon defining the target by a fused cerebral MRI and CT scan. A fully implantable neural telemetry system consisting of a 64 channel intracortical multielectrode array, a telemetry capsule, and an inductive rechargeable battery was then implanted into the visual cortex to record and manipulate local field potentials, and multi-unit activity. We achieved a 3-month stability of the functionality of the un-tethered BCI in terms of telemetric radio-communication, inductive battery charging, and device biocompatibility for 3 months. Finally, we could reliably record the local signature of sub- and suprathreshold neuronal activity in the visual cortex with high bandwidth without complications. The ability to wireless induction charging combined with the entirely implantable design, the rather high recording bandwidth, and the ability to record and stimulate simultaneously put forward a wireless BCI capable of long-term un-tethered real-time communication for causal preclinical circuit-based closed-loop interventions.

A Perspective of International Collaboration Through Web-Based Telecommunication-Inspired by COVID-19 Crisis

The tsunami effect of the COVID-19 pandemic is affecting many aspects of scientific activities. Multidisciplinary experimental studies with international collaborators are hindered by the closing of the national borders, logistic issues due to lockdown, quarantine restrictions, and social distancing requirements. The full impact of this crisis on science is not clear yet, but the above-mentioned issues have most certainly restrained academic research activities. Sharing innovative solutions between researchers is in high demand in this situation. The aim of this paper is to share our successful practice of using web-based communication and remote control software for real-time long-distance control of brain stimulation. This solution may guide and encourage researchers to cope with restrictions and has the potential to help expanding international collaborations by lowering travel time and costs.