The effect of radiation dose on the onset and progression of radiation-induced brain necrosis in the rat model

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.

Investigation of Photodynamic Therapy Promoted by Cherenkov Light Activated Photosensitizers-New Aspects and Revelations

This work investigates the proposed enhanced efficacy of photodynamic therapy (PDT) by activating photosensitizers (PSs) with Cherenkov light (CL). The approaches of Yoon et al. to test the effect of CL with external radiation were taken up and refined. The results were used to transfer the applied scheme from external radiation therapy to radionuclide therapy in nuclear medicine. Here, the CL for the activation of the PSs (psoralen and trioxsalen) is generated by the ionizing radiation from rhenium-188 (a high-energy beta-emitter, Re-188). In vitro cell survival studies were performed on FaDu, B16 and 4T1 cells. A characterization of the PSs (absorbance measurement and gel electrophoresis) and the CL produced by Re-188 (luminescence measurement) was performed as well as a comparison of clonogenic assays with and without PSs. The methods of Yoon et al. were reproduced with a beam line at our facility to validate their results. In our studies with different concentrations of PS and considering the negative controls without PS, the statements of Yoon et al. regarding the positive effect of CL could not be confirmed. There are slight differences in survival fractions, but they are not significant when considering the differences in the controls. Gel electrophoresis showed a dominance of trioxsalen over psoralen in conclusion of single and double strand breaks in plasmid DNA, suggesting a superiority of trioxsalen as a PS (when irradiated with UVA). In addition, absorption measurements showed that these PSs do not need to be shielded from ambient light during the experiment. An observational test setup for a PDT nuclear medicine approach was found. The CL spectrum of Re-188 was measured. Fluctuating inconclusive results from clonogenic assays were found.

Evolution of radiation-induced temporal lobe injury after intensity-modulated radiation therapy in nasopharyngeal carcinoma: a large cohort retrospective study

BACKGROUND

Previous studies have demonstrated conflicting findings regarding the initial MRI patterns of radiotherapy-induced temporal lobe injury (RTLI) and the evolution of different RTLI patterns. The aim of this study was to evaluate the initial MRI pattern and evolution of RTLI in patients with nasopharyngeal carcinoma (NPC) by means of a large cohort study.

METHODS

Data of patients with RTLI were retrospectively collected from two hospitals between January 2011 and December 2021. The injured lobes were categorized into three patterns based on initial MRI patterns: isolated white matter lesions (WMLs), isolated contrast-enhanced lesions (CELs), and combined WMLs and CELs. The latency period, MRI appearances, and temporal changes in WMLs and CELs were evaluated.

RESULTS

A total of 913 RTLI patients with 1092 injured lobes were included in this study. The numbers of isolated WMLs, isolated CELs, and combined WMLs and CELs identified at the first MRI detection were 7 (0.6%), 172 (15.8%), and 913 (83.6%), respectively. The evolution of bilateral RTLI was different in the same patient, and that of unilateral RTLI combined with WMLs and CELs also may occur asynchronously. The time intervals from the initial MRI detection of isolated WMLs, isolated CELs, combined WMLs and CELs to the last negative MRI scan were 8.6, 8.9 and 11.0 months, respectively. A significant difference was observed in the time intervals between the three patterns (H = 14.287, P = 0.001). And the time interval was identified as an independent factor influencing the initial MRI pattern of RTLI after Poisson regression (P = 0.002).

CONCLUSION

Both WMLs and CELs could be the initial and only MRI abnormalities in patients with RTLI. This study is of great significance in accurately diagnosing RTLI early and providing timely treatment options. Additionally, it provides clinical evidence for guidelines on NPC, emphasizing the importance of regular follow-up of NPC patients.

Presence of Activated (Phosphorylated) STAT3 in Radiation Necrosis Following Stereotactic Radiosurgery for Brain Metastases

Brain radiation necrosis (RN) is a subacute or late adverse event following radiotherapy, involving an exacerbated inflammatory response of the brain tissue. The risk of symptomatic RN associated with stereotactic radiosurgery (SRS) as part of the treatment of brain metastases (BMs) has been a subject of recent investigation. The activation of the signal transducer and activator of transcription 3 (STAT3) was shown in reactive astrocytes (RA) associated with BMs. Given that the pathophysiological mechanisms behind RN are not fully understood, we sought to investigate the role of STAT3 among other inflammatory markers in RN development. A mouse model of RN using clinical LINAC-based SRS was designed to induce brain necrosis with the administration of 50 Gy in a single fraction to the left hemisphere using a circular collimator of 5 mm diameter. Immunohistochemistry and multiplex staining for CD4, CD8, CD68, GFAP, and STAT3 were performed. For validation, eleven patients with BMs treated with SRS who developed symptomatic RN and required surgery were identified to perform staining for CD68, GFAP, and STAT3. In the mouse model, the RN and perinecrotic areas showed significantly higher staining for F4/80+ and GFAP+ cells, with a high infiltration of CD4 and CD8 T-lymphocytes, when compared to the non-irradiated cerebral hemisphere. A high number of GFAP+pSTAT3+ and F4/80+pSTAT3+ cells was found in the RN areas and the rest of the irradiated hemisphere. The analysis of human brain specimens showed that astrocytes and microglia were actively phosphorylating STAT3 in the areas of RN and gliosis. Phosphorylated STAT3 is highly expressed in the microglia and RA pertaining to the areas of brain RN. Targeting STAT3 via inhibition represents a promising strategy to ameliorate symptomatic RN in BM patients undergoing SRS.

Psoralen as a Photosensitizers for Photodynamic Therapy by Means of In Vitro Cherenkov Light

Possible enhancements of DNA damage with light of different wavelengths and ionizing radiation (Rhenium-188-a high energy beta emitter (Re-188)) on plasmid DNA and FaDu cells via psoralen were investigated. The biophysical experimental setup could also be used to investigate additional DNA damage due to photodynamic effects, resulting from Cherenkov light. Conformational changes of plasmid DNA due to DNA damage were detected and quantified by gel electrophoresis and fluorescent staining. The clonogene survival of the FaDu cells was analyzed with colony formation assays. Dimethyl sulfoxide was chosen as a chemical modulator, and Re-188 was used to evaluate the radiotoxicity and light (UVC: λ = 254 nm and UVA: λ = 366 nm) to determine the phototoxicity. Psoralen did not show chemotoxic effects on the plasmid DNA or FaDu cells. After additional treatment with light (only 366 nm-not seen with 254 nm), a concentration-dependent increase in single strand breaks (SSBs) was visible, resulting in a decrease in the survival fraction due to the photochemical activation of psoralen. Whilst UVC light was phototoxic, UVA light did not conclude in DNA strand breaks. Re-188 showed typical radiotoxic effects with SSBs, double strand breaks, and an overall reduced cell survival for both the plasmid DNA and FaDu cells. While psoralen and UVA light showed an increased toxicity on plasmid DNA and human cancer cells, Re-188, in combination with psoralen, did not provoke additional DNA damage via Cherenkov light.

Rodent Model of Brain Radionecrosis using Clinical LINAC-based Stereotactic Radiosurgery

Purpose

Methods and Materials

Results

Conclusions

Chronic pathophysiological changes in the normal brain parenchyma caused by radiotherapy accelerate glioma progression

Radiation therapy is one of standard treatment for malignant glioma after surgery. The microenvironment after irradiation is considered not to be suitable for the survival of tumor cells (tumor bed effect). This study investigated whether the effect of changes in the microenvironment of parenchymal brain tissue caused by radiotherapy affect the recurrence and progression of glioma. 65-Gy irradiation had been applied to the right hemisphere of Fisher rats. After 3 months from irradiation, we extracted RNA and protein from the irradiated rat brain. To study effects of proteins extracted from the brains, we performed WST-8 assay and tube formation assay in vitro. Cytokine production were investigated for qPCR. Additionally, we transplanted glioma cell into the irradiated and sham animals and the median survival time of F98 transplanted rats was also examined in vivo. Immunohistochemical analyses and invasiveness of implanted tumor were evaluated. X-ray irradiation promoted the secretion of cytokines such as CXCL12, VEGF-A, TGF-β1 and TNFα from the irradiated brain. Proteins extracted from the irradiated brain promoted the proliferation and angiogenic activity of F98 glioma cells. Glioma cells implanted in the irradiated brains showed significantly high proliferation, angiogenesis and invasive ability, and the post-irradiation F98 tumor-implanted rats showed a shorter median survival time compared to the Sham-irradiation group. The current study suggests that the microenvironment around the brain tissue in the chronic phase after exposure to X-ray radiation becomes suitable for glioma cell growth and invasion.

Risk Factors for Radiation Necrosis in Patients Undergoing Cranial Stereotactic Radiosurgery

Simple Summary

Radiation necrosis is a known complication after stereotactic radiosurgery of intracranial tumors. We evaluated 388 patients who underwent stereotactic radiosurgery at our institution. The most common tumors were metastases (47.2%), followed by vestibular schwannomas (32.2%) and meningiomas (13.4%). 15.7% developed radiation necrosis after a median of 8 months. According to our data, larger tumor diameter (HR 1.065) and higher radiation dose (HR 1.302) were associated with an increased risk of radiation necrosis independently of tumor type. Advanced age was shown to be a risk factor for radiation necrosis only in cases with metastasis (HR 1.066). The data from this study suggest that the development of radiation necrosis is dependent on size and dose, not on the type of the neoplasm.

Abstract

Purpose: single-staged stereotactic radiosurgery (SRS) is an established part of the multimodal treatment in neuro-oncology. Radiation necrosis after high-dose irradiation is a known complication, but there is a lack of evidence about the risk factors. The aim of this study was to evaluate possible risk factors for radiation necrosis in patients undergoing radiosurgery. Methods: patients treated with radiosurgery between January 2004 and November 2020 were retrospectively analyzed. The clinical data, imaging and medication were gathered from electronic patient records. The largest diameter of the tumors was measured using MRI scans in T1 weighted imaging with gadolinium and the edema in T2 weighted sequences. The diagnosis of a radiation necrosis was established analyzing imaging criteria combined with clinical course or pathologically confirmed by subsequent surgical intervention. Patients developing radiation necrosis detected after SRS were compared to patients without evidence of an overshooting irradiation reaction. Results: 388 patients were included retrospectively, 61 (15.7%) of whom developed a radiation necrosis. Median follow-up was 24 (6–62) months with a radiation necrosis after 8 (6–12) months. The most frequent tumors were metastases in 47.2% of the cases, followed by acoustic neuromas in 32.2% and meningiomas in 13.4%. Seventy-three (18.9%) patients already underwent one or more previous radiosurgical procedures for different lesions. The mean largest diameter of the tumors amounted to 16.3 mm (±6.1 mm). The median—80%—isodose administered was 16 (14–25) Gy. Of the radiation necroses, 25 (43.1%) required treatment, in 23 (39.7%) thereof, medical treatment was applied and in 2 (3.4%) cases, debulking surgery was performed. In this study, significantly more radiation necroses arose in patients with higher doses (HR 1.3 [CI 1.2; 1.5], p < 0.001) leading to a risk increment of over 180% between a radiation isodose of 14 and 20 Gy. The maximum diameter was a second significant risk factor (p = 0.028) with an HR of 1065 for every 1 mm increase in multivariate analysis. Conclusion: large diameter and high doses were reliable independent risk factors leading to more frequent radiation necroses, regardless of tumor type in patients undergoing radiosurgery. Alternative therapeutic procedures may be considered in lesions with large volume and an expected high radiation doses due to the increased risk of developing radiation necrosis.

Can Dexmedetomidine Be Effective in the Protection of Radiotherapy-Induced Brain Damage in the Rat?

Approximately 7 million people are reported to be undergoing radiotherapy (RT) at any one time in the world. However, it is still not possible to prevent damage to secondary organs that are off-target. This study, therefore, investigated the potential adverse effects of RT on the brain, using cognitive, histopathological, and biochemical methods, and the counteractive effect of the α2-adrenergic receptor agonist dexmedetomidine. Thirty-two male Sprague Dawley rats aged 5-6 months were randomly allocated into four groups: untreated control, and RT, RT + dexmedetomidine-100, and RT + dexmedetomidine-200-treated groups. The passive avoidance test was applied to all groups. The RT groups received total body X-ray irradiation as a single dose of 8 Gy. The rats were sacrificed 24 h after X-ray irradiation, and following the application of the passive avoidance test. The brain tissues were subjected to histological and biochemical evaluation. No statistically significant difference was found between the control and RT groups in terms of passive avoidance outcomes and 8-hydroxy-2'- deoxyguanosine (8-OHdG) positivity. In contrast, a significant increase in tissue MDA and GSH levels and positivity for TUNEL, TNF-α, and nNOS was observed between the control and the irradiation groups (p < 0.05). A significant decrease in these values was observed in the groups receiving dexmedetomidine. Compared with the control group, gradual elevation was determined in GSH levels in the RT group, followed by the RT + dexmedetomidine-100 and RT + dexmedetomidine-200 groups. Dexmedetomidine may be beneficial in countering the adverse effects of RT in the cerebral and hippocampal regions.

Radiation Effects on Brain Extracellular Matrix

Radiotherapy is an important therapeutic approach to treating malignant tumors of different localization, including brain cancer. Glioblastoma multiforme (GBM) represents the most aggressive brain tumor, which develops relapsed disease during the 1st year after the surgical removal of the primary node, in spite of active adjuvant radiochemotherapy. More and more evidence suggests that the treatment's success might be determined by the balance of expected antitumor effects of the treatment and its non-targeted side effects on the surrounding brain tissue. Radiation-induced damage of the GBM microenvironment might create tumor-susceptible niche facilitating proliferation and invasion of the residual glioma cells and the disease relapse. Understanding of molecular mechanisms of radiation-induced changes in brain ECM might help to reconsider and improve conventional anti-glioblastoma radiotherapy, taking into account the balance between its antitumor and ECM-destructing activities. Although little is currently known about the radiation-induced changes in brain ECM, this review summarizes current knowledge about irradiation effects onto the main components of brain ECM such as proteoglycans, glycosaminoglycans, glycoproteins, and the enzymes responsible for their modification and degradation.

Neuroprotective effect of resveratrol against radiation after surgically induced brain injury by reducing oxidative stress, inflammation, and apoptosis through NRf2/HO-1/NF-κB signaling pathway

The impact of resveratrol (RSV) on radiation (RAD)-induced brain injury in rats' brains was investigated. A total of 40 male Wistar Albino rats were randomly divided into four groups (control, RAD, RAD + RSV, and RSV groups, with 10 rats in each group). The results revealed a significant decrease in catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase activities, as well as glutathione (GSH) content. Further, a significant elevation in malondialdehyde, nitric oxide, interleukin-1-beta (IL-1β), IL-6, and transforming growth factor-β1 levels were observed. Furthermore, decreased B-cell lymphoma 2 (Bcl-2), increased Bcl-2-associated X, and tumor necrosis factor-α genes expression, decreased nuclear factor erythroid-related factor 2, heme oxygenase-1, and increased nuclear factor-κB protein levels were noticed. Also, an apoptosis marker, caspase-3-positive cells, was seen in the hippocampus. Those effects were observed in the RAD group of rats. The treatment of RSV displayed a significant amendment of the studied parameters in the brain tissues of the RAD group of animals. This effect is interrelated to the ability of RSV to scavenge the free radicals, enhance the activity of the antioxidant enzymes, increase GSH contents, and downregulate the inflammatory responses and apoptosis markers in the brain tissues of RAD animals. In conclusion, this study demonstrated that the potent antioxidant, anti-inflammatory, and antiapoptotic activities of RSV can improve the antioxidant status and suppress the inflammatory responses and apoptosis in the brain tissues of RAD animals.

Enhancement radiation-induced apoptosis in C6 glioma tumor-bearing rats via pH-responsive magnetic graphene oxide nanocarrier

5-iodo-2-deoxyuridine (IUdR) has been demonstrated to induce an appreciable radiosensitizing effect on glioblastoma patients, but due to the short circulation half-life times and failure to pass through the blood-brain barrier (BBB), its clinical use is limited. Accordingly, in this study, we used magnetic graphene oxide (NGO/SPIONs) nanoparticles coated with PLGA polymer as a dynamic nanocarrier for IUdR and, evaluated its sensitizing enhancement ratio in combination with a single dose X-ray at clinically megavoltage energies for treatment of C6 glioma rats. Nanoparticles were characterized using Zetasizer and TEM microscopy, and in vitro biocompatibility of nanoparticles was assessed with MTT assay. IUdR/MNPs were intravenously administered under a magnetic field (1.3 T) on day 13 after the implantation of C6 cells. After a day following the injection, rats exposed with radiation (8 Gy). ICP-OES analysis data indicated an effective magnetic targeting, leading to remarkably improved penetration through the BBB. In vivo release analysis with HPLC indicated sustained release of IUdR and, prolonged the lifespan in plasma (P < .01). In addition, our findings revealed a synergistic effect for IUdR/MNPs coupled with radiation, which significantly inhibited the tumor expansion (>100%), prolonged the survival time (>100%) and suppressed the anti-apoptotic response of glioma rats by increasing Bax/Bcl-2 ratio (2.13-fold) in compared with the radiation-only. In conclusion, besides high accumulation in targeted tumor sites, the newly developed IUdR/MNPs, also exhibited the ability of IUdR/MNPs to significantly enhance radiosensitizing effect, improve therapeutic efficacy and increase toxicity for glioma-bearing rats.

Influence of Dose Uniformity when Replicating a Gamma Knife Mouse Model of Radiation Necrosis with a Preclinical Irradiator

A common mouse model used for studying radiation necrosis is generated with the gamma knife, which has a non-uniform dose distribution. The goal of this study was to determine whether the lesion growth observed in this mouse model is a function of non-uniform dose distribution and/or lesion progression. Here, a model similar to the gamma knife mouse model was generated; using a preclinical irradiator, mice received single-fraction doses from 50 to 100 Gy to a sub-hemispheric portion of the brain. The development of necrosis was tracked for up to 26 weeks with a 7T Bruker magnetic resonance imaging (MRI) scanner using T2 and post-contrast T1 imaging. MRI findings were validated with histology, specifically H&E staining. Single small beam 50 Gy irradiations failed to produce necrosis in a 26-week span, while doses from 60 to 100 Gy produced necrosis in a timeframe ranging from 16 weeks to 2 weeks, respectively. Postmortem histology confirmed pathological development in regions corresponding with those that showed abnormal signal on MRI. The growth of the necrotic lesion observed in this gamma knife model was due in part to a non-uniform dose distribution rather than to the increased severity of the lesion. Interpretation of results from the gamma knife model must take into consideration the potential effect of nonuniform dose distribution, particularly with regards to the timing of interventions. There are time points in this model at which pre-onset, onset and post-onset of radiation necrosis are all represented in the irradiated field.

Label-free fluorescence lifetime spectroscopy detects radiation-induced necrotic changes in live brain in real-time

Current clinical imaging modalities do not reliably identify brain tissue regions with necrosis following radiotherapy. This creates challenges for stereotaxic biopsies and surgical-decision making. Time-resolved fluorescence spectroscopy (TRFS) provides a means to rapidly identify necrotic tissue by its distinct autofluorescence signature resulting from tissue breakdown and altered metabolic profiles in regions with radiation damage. Studies conducted in a live animal model of radiation necrosis demonstrated that necrotic tissue is characterized by respective increases of 27% and 108% in average lifetime and redox ratio, when compared with healthy tissue. Moreover, radiation-damaged tissue not visible by MRI but confirmed by histopathology, was detected by TRFS. Current results demonstrate the ability of TRFS to identify radiation-damaged brain tissue in real-time and indicates its potential to assist with surgical guidance and MRI-guided biopsy procedures.