Synchrotron Microbeam Radiation Research Articles

The Impact of Synchrotron Microbeam Radiation Therapy Combined With Broad Beam in a Preclinical Breast Cancer Model

PURPOSEBoth local tumor control and distant metastasis are important indicators of the efficacy of radiotherapy treatment. Synchrotron Microbeam Radiotherapy (MRT), spatially fractionated radiation delivered at ultra-high dose-rates, shows remarkable normal tissue sparing with excellent local control in some models. Some MRT regimens trigger an antitumor immune response that contributes not only to the local, but also to systemic treatment efficacy. Despite recent advances for treatment of primary breast cancer, metastatic disease is still the major cause of treatment failure in the clinic. Here, in an aggressive preclinical triple-negative breast cancer model, we compared local tumor response and metastasis following different MRT treatment programs. EXPERIMENTAL DESIGN4T1.2 mouse mammary tumors were treated with 300-Gy peak-/7-Gy valley-dose MRT and/or 8-Gy broad-beam (BB) radiation, all delivered as daily fractionated programs (three consecutive daily sessions of either MRT or BB, or one MRT combined with two BB sessions, the first or last of the three fractions). The mice were euthanized on day 9 post-last irradiation, when unirradiated control animals reached ethical endpoint. Primary tumors were collected to evaluate immune cell prevalence, while lungs, spinal cords, and locoregional lymph nodes were collected to measure metastatic burden. In parallel, local tumor growth and survival were monitored. RESULTSThe combined MRT/BB treatment shifted the balance between pro- and anti-tumorigenic macrophages towards accumulation of anti-tumorigenic macrophages in the tumor. Monitoring of the tumor volume and animal health indicated the benefit of the combined MRT/BB treatment for local control and treatment tolerance, while animal survival was only marginally longer for one combined schedule. The metastatic burden was similar for all four treatment schedules. CONCLUSIONAddition of single MRT to BB treatment improved the primary tumor response. This provides a basis for future experiments incorporating adjuvant immunotherapy or chemotherapy, to improve local and systemic treatment outcomes.

1691: Clinical transfer of synchrotron microbeam radiation therapy: Canine brain tumor phase I study

1691: Clinical transfer of synchrotron microbeam radiation therapy: Canine brain tumor phase I study

Neuro-Oncologic Veterinary Trial for the Clinical Transfer of Microbeam Radiation Therapy: Acute to Subacute Radiotolerance after Brain Tumor Irradiation in Pet Dogs.

Synchrotron Microbeam Radiation Therapy (MRT) has repeatedly proven its superiority compared with conventional radiotherapy for glioma control in preclinical research. The clinical transfer phase of MRT has recently gained momentum; seven dogs with suspected glioma were treated under clinical conditions to determine the feasibility and safety of MRT. We administered a single fraction of 3D-conformal, image-guided MRT. Ultra-high-dose rate synchrotron X-ray microbeams (50 µm-wide, 400 µm-spaced) were delivered through five conformal irradiation ports. The PTV received ~25 Gy peak dose (within microbeams) per port, corresponding to a minimal cumulated valley dose (diffusing between microbeams) of 2.8 Gy. The dogs underwent clinical and MRI follow-up, and owner evaluations. One dog was lost to follow-up. Clinical exams of the remaining six dogs during the first 3 months did not indicate radiotoxicity induced by MRT. Quality of life improved from 7.3/10 [±0.7] to 8.9/10 [±0.3]. Tumor-induced seizure activity decreased significantly. A significant tumor volume reduction of 69% [±6%] was reached 3 months after MRT. Our study is the first neuro-oncologic veterinary trial of 3D-conformal Synchrotron MRT and reveals that MRT does not induce acute to subacute radiotoxicity in normal brain tissues. MRT improves quality of life and leads to remarkable tumor volume reduction despite low valley dose delivery. This trial is an essential step towards the forthcoming clinical application of MRT against deep-seated human brain tumors.

Neurologic Changes Induced by Whole-Brain Synchrotron Microbeam Irradiation: 10-Month Behavioral and Veterinary Follow-Up

PurposeNovel radiotherapy approaches have increased the therapeutic efficacy for malignant brain tumors over the last decades but the balance between therapeutic gain and radiotoxicity remains a medical hardship. Synchrotron Microbeam Radiation Therapy (MRT), an innovative technique, deposes extremely high (peak) doses in micron-wide, parallel microbeam paths, while the diffusing inter-beam (valley) doses lie in the range of conventional radiotherapy doses. In this study, we evaluated normal tissue toxicity of whole-brain microbeam irradiation (MBI) versus that of a conventional, hospital broad beam (hBB). Methods and MaterialsNormal Fischer rats (n=6-7/group) were irradiated with one of the two modalities, exposing the entire brain to 0, 5/200, 10/400, 13/520, 17/680 or 25/1000 Gy MBI valley/peak dose, or to 7, 10, 13, 17 or 25 Gy hBB dose. Two additional groups of rats received 10 Gy MBI valley dose coupled with 7 or 15 Gy BB dose (groups MBI17* and MBI25*). Behavioral parameters were evaluated for 10 months post irradiation, combined with veterinary observations. ResultsMBI peak doses of ≥680 Gy caused acute toxicity and death. Animals exposed to hBB or MBI dose-dependently gained less weight than controls; rats in the hBB25 and MBI25* groups deceased within 6 months post irradiation. Increasing doses of MBI caused hyperactivity but no other detectable behavioral alteration in our tests. Importantly, no health concerns were seen up to 17 Gy MBI valley dose. ConclusionsWhile acute toxicity of microbeam exposures depends on very high peak doses, late toxicity mainly relates to delivery of high MBI valley doses. MBI seems to elicit low impact on normal rat behavior but further tests are warranted to fully explore this hypothesis. However, high peak and valley doses are well tolerated from a veterinary point of view. This normal tissue tolerance to whole-brain, high-dose MBI reveals a promising avenue for MRT, i.e., therapeutic applications of microbeams which are poised for translation to a clinical environment.

Treatment planning with high-resolution 3D dose maps in preclinical and translational synchrotron microbeam radiation therapy

Background and PurposeMicrobeam Radiation Therapy (MRT) aims to deliver higher doses to the target while minimizing radiation damage to healthy tissues using synchrotron x-ray microbeams. Translational MRT research has now started, driven by promising results from preclinical studies. This study aimed to propose a first dose-outcome model by analyzing micrometric dose distributions obtained with high-resolution 3D dose calculations, accounting for the inherent physical dose distribution complexity in MRT. The feasibility of integrating penMRT, our full Monte Carlo multiscale dose calculation algorithm based on PENELOPE into translational research on veterinary patients was also investigated. Material and MethodsMicrometric dose distributions were calculated in tumor-bearing rats and for a veterinary patient with penMRT, for conformal multi-directional MRT treatment plans. Absorbed dose maps were obtained with 0.005 × 0.005 × 1 mm3 voxel sizes. High-resolution dose-volume histograms were extracted and analyzed against radiobiology studies. ResultsThe complexity of the MRT dose distribution was properly rendered at a micrometer scale on 3D dose maps, with well separated dose regions observed on the differential dose-volume histograms. The median survival time of glioma-bearing rats varied linearly with the volume fraction of the planning target volume that received doses higher than 50 Gy (R2 = 0.98). The feasibility of using penMRT for treatment planning in large volumes has been shown on a veterinary patient. ConclusionsThis study demonstrated the significant added value of penMRT for planning and prescribing MRT treatments. It also shed light on the correlation between the high-resolution 3D dose distributions and the treatment outcome.

Modulating Synchrotron Microbeam Radiation Therapy Doses for Preclinical Brain Cancer

Synchrotron Microbeam Radiation Therapy (MRT) is an innovative technique that spatially segments the synchrotron radiation field for cancer treatment. A microbeam peak dose is often hundreds of times the dose in the valley (the sub-millimeter region between the peaks of the microbeams). Peak and valley doses vary with increasing depth in tissue which effects tumor dose coverage. It remains to be seen whether the peak or valley is the primary factor in MRT cancer control. This study investigates how unilateral MRT doses can be modulated using a bolus, and identifies the valley dose as a primary factor in MRT cancer control. Fischer rats bearing 9 L gliosarcoma tumors were irradiated with MRT at the Imaging and Medical Beam Line of the Australian Synchrotron. MRT valley doses of 8–15 Gy (250–1040 Gy peak doses) were used to treat tumors with and without a 5 mm dose-modulating bolus. Long-term survival depended on the valley dose primarily (92% correlation), and the use of the bolus reduced the variance in animal survival and improved to the mean survival of rats treated with MRT by 47% and 18% using 15 Gy and 8 Gy valley doses, respectively.

Monocrystalline diamond detector for online monitoring during synchrotron microbeam radiotherapy.

Microbeam radiation therapy (MRT) is a radiotherapy technique combining spatial fractionation of the dose distribution on a micrometric scale, X-rays in the 50-500 keV range and dose rates up to 16 × 103 Gy s-1. Nowadays, in vivo dosimetry remains a challenge due to the ultra-high radiation fluxes involved and the need for high-spatial-resolution detectors. The aim here was to develop a striped diamond portal detector enabling online microbeam monitoring during synchrotron MRT treatments. The detector, a 550 µm bulk monocrystalline diamond, is an eight-strip device, of height 3 mm, width 178 µm and with 60 µm spaced strips, surrounded by a guard ring. An eight-channel ASIC circuit for charge integration and digitization has been designed and tested. Characterization tests were performed at the ID17 biomedical beamline of the European Synchrotron Radiation Facility (ESRF). The detector measured direct and attenuated microbeams as well as interbeam fluxes with a precision level of 1%. Tests on phantoms (RW3 and anthropomorphic head phantoms) were performed and compared with simulations. Synchrotron radiation measurements were performed on an RW3 phantom for strips facing a microbeam and for strips facing an interbeam area. A 2% difference between experiments and simulations was found. In more complex geometries, a preliminary study showed that the absolute differences between simulated and recorded transmitted beams were within 2%. Obtained results showed the feasibility of performing MRT portal monitoring using a microstriped diamond detector. Online dosimetric measurements are currently ongoing during clinical veterinary trials at ESRF, and the next 153-strip detector prototype, covering the entire irradiation field, is being finalized at our institution.

Hydrogenated amorphous silicon high flux x-ray detectors for synchrotron microbeam radiation therapy

Objective. Microbeam radiation therapy (MRT) is an alternative emerging radiotherapy treatment modality which has demonstrated effective radioresistant tumour control while sparing surrounding healthy tissue in preclinical trials. This apparent selectivity is achieved through MRT combining ultra-high dose rates with micron-scale spatial fractionation of the delivered x-ray treatment field. Quality assurance dosimetry for MRT must therefore overcome a significant challenge, as detectors require both a high dynamic range and a high spatial resolution to perform accurately. Approach. In this work, a series of radiation hard a-Si:H diodes, with different thicknesses and carrier selective contact configurations, have been characterised for x-ray dosimetry and real-time beam monitoring applications in extremely high flux beamlines utilised for MRT at the Australian Synchrotron. Results. These devices displayed superior radiation hardness under constant high dose-rate irradiations on the order of 6000 Gy s−1, with a variation in response of 10% over a delivered dose range of approximately 600 kGy. Dose linearity of each detector to x-rays with a peak energy of 117 keV is reported, with sensitivities ranging from (2.74 ± 0.02) nC/Gy to (4.96 ± 0.02) nC/Gy. For detectors with 0.8 μm thick active a-Si:H layer, their operation in an edge-on orientation allows for the reconstruction of micron-size beam profiles (microbeams). The microbeams, with a nominal full-width-half-max of 50 μm and a peak-to-peak separation of 400 μm, were reconstructed with extreme accuracy. The full-width-half-max was observed as 55 ± 1 μm. Evaluation of the peak-to-valley dose ratio and dose-rate dependence of the devices, as well as an x-ray induced charge (XBIC) map of a single pixel is also reported. Significance. These devices based on novel a-Si:H technology possess a unique combination of accurate dosimetric performance and radiation resistance, making them an ideal candidate for x-ray dosimetry in high dose-rate environments such as FLASH and MRT.

MRT-boost as the last fraction may be the most efficient irradiation schedule for increased survival times in a rat glioma model.

Synchrotron microbeam radiation therapy (MRT) is based on the spatial fractionation of the incident synchrotron beam into arrays of parallel microbeams, typically a few tens of micrometres wide and depositing several hundred Gray. This high dose, high dose rate, spatially fractionated radiotherapy has a high therapeutic impact on tumors, especially in intracranial locations. MRT leads to better control of incurable high-grade glioma than from homogeneous radiotherapy. The schedule of MRT within a conventional irradiation protocol (three fractions of 11 Gy) of brain tumors was evaluated on the 9L glioma model in rats. MRT delivered as a first fraction increased the median survival time of the animals by four days compared with conventional radiotherapy, while the last MRT fraction improved the lifespan by 148% (+15.5 days compared with conventional radiotherapy, p < 0.0001). The most efficient radiation regimen was obtained when the MRT-boost was applied as the last fraction, following two conventional clinical exposures.

Comparison of the dosimetric response of two Sr salts irradiated with 60Co γ-rays and synchrotron X-rays at ultra-high dose rate

As part of the development of innovative radiotherapy techniques using X-ray synchrotron sources, namely FLASH-radiotherapy and microbeam radiation therapy (MRT), two rod dosimeters based on strontium sulfate (SrSO4) and strontium carbonate (SrCO3) were developed and irradiated at the ESRF-ID17 Biomedical beamline to investigate new solid-state dosimeters.The radiation-induced defect in Sr-based dosimeters was detected by means of an electron paramagnetic resonance (EPR) spectrometer. For the study, the EPR response of the dosimeters irradiated with synchrotron X-rays in the 30–600 keV range and dose rate of 11.6 kGy/s was compared with the response after irradiation with a 60Co γ-ray source with a dose rate of 0.288 Gy/s.Both Sr dosimeters show an increased intensity of the EPR signal in the case of irradiation at the synchrotron with respect to the case of 60Co γ-ray irradiation. The measured enhancement of the delivered dose is explained by the fact that Sr shows an increased photoelectric interaction at orthovoltage X-ray energies, producing an increased number of free radicals.The experimental relative response rESRF of the EPR signals between samples irradiated at the ID17 beamline and the 60Co beam quality was found to be 9.66 for SrSO4 and 11.19 for SrCO3. Meanwhile, the theoritical relative responses rμen/ρESRF calculated as the ratio of mass energy absorption coefficients (μen/ρ) of the dosimeters to that for water at the ID17 with respect to the 60Co beam was found to be 11.85 for SrSO4 and 13.31 for SrCO3.The increased EPR response of Sr salt dosimeters irradiated with photons in the keV range proved that these detectors type could be a good candidate for the development of very sensible detectors for radiotherapy applications.

Therapeutic Strategies and Metal-Induced Oxidative Stress: Application of Synchrotron Radiation Microbeam to Amyotrophic Lateral Sclerosis in the Kii Peninsula of Japan.

A series of extensive gene-environment studies on amyotrophic lateral sclerosis (ALS) and Parkinsonism–dementia complex (PDC) in Guam Island, USA, and the Kii Peninsula of Japan, including Auyu Jakai, West New Guinea, have led us to hypothesize that a prolonged low calcium (Ca) and magnesium (Mg) intake, especially over generation, may cause oxidative stress to motor and nigral neurons by an increased uptake of environment metallic elements, i.e., aluminum (Al), manganese (Mn), and iron (Fe). Otherwise, 5–10% of total ALS cases are familial ALS (fALS), of which 20% of the fALS cases linked to a point mutation of Cu/Zn superoxide dismutase (SOD1). In the vicinity of the Kii Peninsula, about 7% of the ALS cases are also linked to the SOD1 mutation. Using synchrotron radiation (SR) microbeam, conglomerate inclusion (SOD1 aggregates) within a spinal motor neuron of the fALS case in the vicinity revealed a loss of copper (Cu) in contrast to extremely high contents of Zinc (Zn) and Ca. That means an exceptionally low Cu/Zn ratio with an increased Ca content, indicating the abnormalities of the active site of SOD1 protein of the fALS. Furthermore, sALS in the southernmost high incidence areas of the Kii Peninsula showed a low Cu/Zn ratio within a motor neuron, suggesting a fragility of SOD1 proteins. From the perspective of gene–environment interactions, the above two research trends may show a common oxidative stress underlying the neuronal degenerative process of ALS/PDC in the Kii Peninsula of Japan. Therefore, it is a crucial point for the prospect of therapeutic strategy to clarify a role of transition metals in the oxidative process in both ALS/PDC, including ALS elsewhere in the world. This paper reviews a history of the genetic epidemiological studies, especially from the aspect of gene–environment interaction, on ALS/PDC in the Kii and Guam high incidence foci and the results of a series of analytical research on trace metallic elements within neurons of both sALS and fALS cases, especially using a synchrotron radiation (SR) microbeam of Spring-8 and Photon Factory of Japan. The SR microbeam is an ideal X-ray source, which supplies an extremely high brilliance (high-intensity photon) and tunability (energy variability) to investigate trace metallic elements contained in biological specimens at the cellular level, even more without any damages. This research will provide a valuable information about the mechanism of oxidative stress involved in neuronal cell death in ALS and related neurodegenerative disorders. To elucidate the physicochemical mechanism of the oxidative process in neuronal degeneration, it will shed a new light on the therapeutic strategies for ALS/PDC in near future.

Toward Neuro-Oncologic Clinical Trials of High-Dose-Rate Synchrotron Microbeam Radiation Therapy: First Treatment of a Spontaneous Canine Brain Tumor

The high potential of microbeam radiation therapy (MRT) in improving tumor control while reducing side effects has been shown by numerous preclinical studies. MRT offers a widened therapeutic window by using the periodical spatial fractionation of synchrotron generated x-rays into an array of intense parallel microbeams. MRT now enters a clinical transfer phase. As proof of principle and cornerstone for the safe clinical transfer of MRT, we conducted a "first in dog" trial under clinical conditions. In this report, we evaluated whether a 3-dimensional conformal MRT can be safely delivered as exclusive radiosurgical treatment in animal patients METHODS AND MATERIALS: We irradiated a 17.5-kg French bulldog for a spontaneous brain tumor (glioma suspected on magnetic resonance imaging) with conformal high-dose-rate microbeam arrays (50-µm-wide microbeams, replicated with a pitch of 400 μm) of synchrotron-generated x-rays. The dose prescription adjusted a minimal cumulated valley dose of 2.8 Gy to the plnning target volume (PTV) (cinical target volume (CTV)+1 mm). Thus, each beam delivered 20 to 25 Gy to the target as peak doses, and ∼1 Gy as valley doses RESULTS: The treatment was successfully delivered. Clinical follow-up over 3 months showed a significant improvement of the dog's quality of life: the symptoms disappeared. Magnetic resonance imaging, performed 3 months after irradiation, revealed reduction in tumor size (-87.4%) and mass effect with normalization of the left lateral ventricle. To our knowledge, this neuro-oncologic veterinary trial is the first 3-dimensional conformal synchrotron x-ray MRT treatment of a spontaneous intracranial tumor in a large animal. It is an essential last step toward the clinical transfer of MRT in the near future to demonstrate the feasibility and safety of treating deep-seated tumors using synchrotron-generated microbeams.

Meloxicam can Potentiate the Therapeutic Effects of Synchrotron Microbeam Radiation Therapy on High-Grade Glioma Bearing Rats.

The microbeam radiation therapy (MRT), a spatially micro-fractionated synchrotron radiotherapy, leads to better control of incurable high-grade glioma than that obtained upon homogeneous radiotherapy. We evaluated the effect of meloxicam, a non-steroidal anti-inflammatory drug (NSAID), to increase the MRT response. Survival of rats bearing intracranial 9L gliosarcoma treated with meloxicam and/or MRT (400 Gy, 50 µm-wide microbeams, 200 µm spacing) was monitored. Tumor growth was assessed on histological tissue sections and COX-2 transcriptomic expression was studied 1 to 25 days after radiotherapy. Meloxicam significantly extended the median survival of microbeam-irradiated rats (from +10.5 to +20 days). Dual treatment led to last survivors until D90 (D39 for the MRT group) and to tumor 9.5 times smaller than MRT alone. No significant modification of COX-2 expression was induced by MRT in normal and tumor tissues. The meloxicam reinforced the anti-tumor effect of MRT for glioma treatment. Although the mechanisms of interaction between meloxicam and MRT remain to be elucidated, the addition of this NSAID, easily implemented as a supplement to water for example, is a very favorable therapeutic regimen since it doubled the survival benefit compared to MRT alone.

O042 - FLASH Modalities Track (Oral Presentations) SYNCHROTRON MICROBEAM RADIATION: FLASH AND SPATIAL FRACTIONATION, THE BEST OF BOTH WORLDS

O042 - FLASH Modalities Track (Oral Presentations) SYNCHROTRON MICROBEAM RADIATION: FLASH AND SPATIAL FRACTIONATION, THE BEST OF BOTH WORLDS

Heterogeneous Nucleation Effects of Talc Particles on Polymorphic Crystallization of Cocoa Butter

Polymorphic crystallization of cocoa butter (CB) in a bulk system was examined for the influence of adding talc particles at different concentrations (0.1–5%). While the system was cooled from the melt and subsequently heated, changes in the heat flow and crystal structure of CB were analyzed using differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffraction (SR-XRD). Synchrotron radiation microbeam X-ray diffraction (SR-μ-XRD) was employed to determine lamellar-plane directions of CB crystals occurring with talc addition. At any cooling rates (0.1–15 °C/min) applied, talc promoted CB crystallization to elevate the onset crystallization temperature logarithmically with the increasing concentration of talc; this effect became more prominent at higher cooling rates. Talc also acted as a polymorphic stabilizer so that CB crystallized in more stable forms even when cooled at highest rate of 15 °C/min. Moreover, a highly ordered lamellar-plane direction was extensively observed for CB crystals occurring with 0.1% talc addition, which was disturbed by 0.5% talc addition probably due to the spatial dispersion of densely populated talc particles in their randomized orientation. These heterogeneous nucleation effects indicate the potential of talc particles to be used for the quality and productivity control of CB-based products.

Incorporating Clinical Imaging into the Delivery of Microbeam Radiation Therapy

Synchrotron microbeam radiation therapy is a promising pre-clinical radiation treatment modality; however, it comes with many technical challenges. This study describes the image guidance protocol used for Australia’s first long-term pre-clinical MRT treatment of rats bearing 9L gliosarcoma tumours. The protocol utilises existing infrastructure available at the Australian Synchrotron and the adjoining Monash Biomedical Imaging facility. The protocol is designed and optimised to treat small animals utilising high-resolution clinical CT for patient specific tumour identification, coupled with conventional radiography, using the recently developed SyncMRT program for image guidance. Dosimetry performed in small animal phantoms shows patient dose is comparable to standard clinical doses, with a CT associated dose of less than 1.39cGy and a planar radiograh dose of less than 0.03cGy. Experimental validation of alignment accuracy with radiographic film demonstrates end to end accuracy of less than ±0.34mm in anatomical phantoms. Histological analysis of tumour-bearing rats treated with microbeam radiation therapy verifies that tumours are targeted well within applied treatment margins. To date, this technique has been used to treat 35 tumour-bearing rats.

Synchrotron Microbeam Radiation Therapy for the Treatment of Lung Carcinoma: A Preclinical Study

In the past 3 decades, synchrotron microbeam radiation therapy (S-MRT) has been shown to achieve both good tumor control and normal tissue sparing in a range of preclinical animal models. However, the use of S-MRT for the treatment of lung tumors has not yet been investigated. This study is the first to evaluate the therapeutic efficacy of S-MRT for the treatment of lung carcinoma, using a new syngeneic and orthotopic mouse model. Lewis Lung carcinoma-bearing mice were irradiated with 2 cross-fired arrays of S-MRT or synchrotron broad-beam (S-BB) radiation therapy. S-MRT consisted of 17 microbeams with a width of 50 µm and center-to-center spacing of 400 µm. Each microbeam delivered a peak entrance dose of 400 Gy whereas S-BB delivered a homogeneous entrance dose of 5.16 Gy (corresponding to the S-MRT valley dose). Both treatments prolonged the survival of mice relative to the untreated controls. However, mice in the S-MRT group developed severe pulmonary edema around the irradiated carcinomas and did not have improved survival relative to the S-BB group. Subsequent postmortem examination of tumor size revealed that the mice in the S-MRT group had notably smaller tumor volume compared with the S-BB group, despite the presence of edema. Mice that were sham-implanted did not display any decline in health after S-MRT, experiencing only mild and transient edema between 4 days and 3 months postirradiation which disappeared after 4 months. Finally, a parallel study investigating the lungs of healthy mice showed the complete absence of radiation-induced pulmonary fibrosis 6 months after S-MRT. S-MRT is a promising tool for the treatment of lung carcinoma, reducing tumor size compared with mice treated with S-BB and sparing healthy lungs from pulmonary fibrosis. Future experiments should focus on optimizing S-MRT parameters to minimize pulmonary edema and maximize the therapeutic ratio.

Spatially Fractionated X-Ray Microbeams Elicit a More Sustained Immune and Inflammatory Response in the Brainstem than Homogenous Irradiation.

Synchrotron microbeam radiation therapy (MRT) is a preclinical irradiation technique which could be used to treat intracranial malignancies. The goal of this work was to discern differences in gene expression and the predicted regulation of molecular pathways in the brainstem after MRT versus synchrotron broad-beam radiation therapy (SBBR). Healthy C57BL/6 mice received whole-head irradiation with median acute toxic doses of MRT (241 Gy peak dose) or SBBR (13 Gy). Brains were harvested 4 and 48 h postirradiation and RNA was extracted from the brainstem. RNA-sequencing was performed to identify differentially expressed genes (false discovery rate < 0.01) relative to nonirradiated controls and significantly regulated molecular pathways and biological functions were identified (Benjamini-Hochberg corrected P < 0.05). Differentially expressed genes and regulated pathways largely reflected a pro-inflammatory response 4 h after both MRT and SBBR which was sustained at 48 h postirradiation for MRT. Pathways relating to radiation-induced viral mimicry, including HMGB1, NF-κB and interferon signaling cascades, were predicted to be uniquely activated by MRT. Local microglia, as well as circulating leukocytes, including T cells, were predicted to be activated by MRT. Our findings affirm that the transcriptomic signature of MRT is distinct from broad-beam radiotherapy, with a sustained inflammatory and immune response up to 48 h postirradiation.

The γH2AX DSB marker may not be a suitable biodosimeter to measure the biological MRT valley dose

Purpose γH2AX biodosimetry has been proposed as an alternative dosimetry method for microbeam radiation therapy (MRT) because conventional dosimeters, such as ionization chambers, lack the spatial resolution required to accurately measure the MRT valley dose. Here we investigated whether γH2AX biodosimetry should be used to measure the biological valley dose of MRT-irradiated mammalian cells. Materials and methods We irradiated human skin fibroblasts and mouse skin flaps with synchrotron MRT and broad beam (BB) radiation. BB doses of 1–5 Gy were used to generate a calibration curve in order to estimate the biological MRT valley dose using the γH2AX assay. Results Our key finding was that MRT induced a non-linear dose response compared to BB, where doses 2–3 times greater showed the same level of DNA DSB damage in the valley in cell and tissue studies. This indicates that γH2AX may not be an appropriate biodosimeter to estimate the biological valley doses of MRT-irradiated samples. We also established foci yields of 5.9 ± and 27.4 ± foci/cell/Gy in mouse skin tissue and human fibroblasts respectively, induced by BB. Using Monte Carlo simulations, a linear dose response was seen in cell and tissue studies and produced predicted peak-to-valley dose ratios (PVDRs) of ∼30 and ∼107 for human fibroblasts and mouse skin tissue respectively. Conclusions Our report highlights novel MRT radiobiology, attempts to explain why γH2AX may not be an appropriate biodosimeter and suggests further studies aimed at revealing the biological and cellular communication mechanisms that drive the normal tissue sparing effect, which is characteristic of MRT.

Unexpected Benefits of Multiport Synchrotron Microbeam Radiation Therapy for Brain Tumors

Simple SummaryWe unveiled the potential of an innovative irradiation technique that ablates brain cancer while sparing normal tissues. Spatially fractionating the incident beam into arrays of micrometer-wide beamlets of X-rays (MRT for Microbeam Radiation Therapy) has led to significantly increased survival and tumor control in preclinical studies. Multiport MRT versus conventional irradiations, for the same background continuous dose, resulted in unexpectedly high equivalent biological effects in rats that have not been achieved with any other radiotherapeutic method. These hallmarks of multiport MRT, i.e., minimal impact on normal tissues and exceptional tumor control, may promote this method towards clinical applications, possibly increasing survival and improving long-term outcomes in neuro-oncology patients.Delivery of high-radiation doses to brain tumors via multiple arrays of synchrotron X-ray microbeams permits huge therapeutic advantages. Brain tumor (9LGS)-bearing and normal rats were irradiated using a conventional, homogeneous Broad Beam (BB), or Microbeam Radiation Therapy (MRT), then studied by behavioral tests, MRI, and histopathology. A valley dose of 10 Gy deposited between microbeams, delivered by a single port, improved tumor control and median survival time of tumor-bearing rats better than a BB isodose. An increased number of ports and an accumulated valley dose maintained at 10 Gy delayed tumor growth and improved survival. Histopathologically, cell death, vascular damage, and inflammatory response increased in tumors. At identical valley isodose, each additional MRT port extended survival, resulting in an exponential correlation between port numbers and animal lifespan (r2 = 0.9928). A 10 Gy valley dose, in MRT mode, delivered through 5 ports, achieved the same survival as a 25 Gy BB irradiation because of tumor dose hot spots created by intersecting microbeams. Conversely, normal tissue damage remained minimal in all the single converging extratumoral arrays. Multiport MRT reached exceptional ~2.5-fold biological equivalent tumor doses. The unique normal tissue sparing and therapeutic index are eminent prerequisites for clinical translation.