Background and Aims

Microbeam Radiation Therapy (MRT) is an innovative radiotherapeutic approach by which synchrotron-generated X-rays are spatially fractionated resulting in periodic, alternating dose distribution in the tissue. In parallel to the excellent tumour control, normal tissues show remarkably high resistance. However, the biggest challenge in translating MRT to the clinic are the high peak doses (300-600Gy) delivered at ultra-fast dose-rates, achievable currently only by synchrotron facilities. Therefore, to advance the clinical translation of MRT, new treatment strategies have been explored.

Methods

Microbeam Radiation Therapy, single 400Gy, fractionated (3x133Gy), combination with Au-NP and cisplatin

Results

We have demonstrated that temporally fractionated MRT (3x 133Gy) ablated 50% of murine melanomas, preventing organ metastases and local recurrence for 18 months post-treatment. In the remaining animals, the median survival increased by 2.5-fold compared to single MRT-irradiated mice and by 4.1-fold relative to untreated mice. In a double treatment, 150Gy MRT combined with Au-NP increased the median survival by more than 2-fold compared to a single MRT irradiation, and 6.6-fold compared to untreated mice. Furthermore, 150Gy MRT, when combined with cisplatin, reduced the glioblastoma tumour volume by 6-fold compared to cisplatin alone and 60-fold relative to untreated mice.
Temporally fractionated MRT and low dose MRT combined with Au-NP or cisplatin increased the efficacy of MRT in the case of radioresistant melanoma and glioblastoma, reaching the best reported treatment ratio for complete tumour remission.

Conclusions

Our results demonstrate that MRT administration could be adapted for clinical use by employing multiple fractions with lower peak doses using intersecting arrays or with combined treatment strategies.

Background and Aims

Microbeam Radiation Therapy (MRT) is an innovative radiotherapeutic approach by which synchrotron-generated X-rays are spatially fractionated resulting in periodic, alternating dose distribution in the tissue. In parallel to the excellent tumour control, normal tissues show remarkably high resistance. However, the biggest challenge in translating MRT to the clinic are the high peak doses (300-600Gy) delivered at ultra-fast dose-rates, achievable currently only by synchrotron facilities. Therefore, to advance the clinical translation of MRT, new treatment strategies have been explored.

Methods

Microbeam Radiation Therapy, single 400Gy, fractionated (3x133Gy), combination with Au-NP and cisplatin

Results

We have demonstrated that temporally fractionated MRT (3x 133Gy) ablated 50% of murine melanomas, preventing organ metastases and local recurrence for 18 months post-treatment. In the remaining animals, the median survival increased by 2.5-fold compared to single MRT-irradiated mice and by 4.1-fold relative to untreated mice. In a double treatment, 150Gy MRT combined with Au-NP increased the median survival by more than 2-fold compared to a single MRT irradiation, and 6.6-fold compared to untreated mice. Furthermore, 150Gy MRT, when combined with cisplatin, reduced the glioblastoma tumour volume by 6-fold compared to cisplatin alone and 60-fold relative to untreated mice.
Temporally fractionated MRT and low dose MRT combined with Au-NP or cisplatin increased the efficacy of MRT in the case of radioresistant melanoma and glioblastoma, reaching the best reported treatment ratio for complete tumour remission.

Conclusions

Our results demonstrate that MRT administration could be adapted for clinical use by employing multiple fractions with lower peak doses using intersecting arrays or with combined treatment strategies.

Background and Aims

Experimental synchrotron X-ray-generated microbeam radiation therapy (MRT) represents an innovative mode of cancer radiotherapy with an excellent therapeutic ratio, but optimization of the irradiation protocol is an essential step toward clinical implementation.

Methods

We irradiated B16-F10 melanoma-bearing C57BL/6J female mice with one or two 396-Gy peak-dose fractions of MRT.

Results

The second MRT fraction remarkably attenuated tumour growth. Both single dose MRT and broad beam irradiation quickly accelerated the formation of metastasis in superficial cervical lymph nodes. Remarkably, the second MRT fraction triggered a very pronounced regression of locoregional metastasis that lasted for 5 weeks. This reduction cannot be explained by direct exposure of melanoma cells to low-dose scattered radiation, therefore an abscopal effect is a legitimate explanation. In search for factors that generated this anti-tumor/anti-metastatic response, we measured plasma concentrations of 34 pro-inflammatory and anti-inflammatory cytokines in cohorts of mice that received one or two MRT fractions. Neutrophil and T cell-attracting chemokines CXCL5, CXCL12 and CCL22 were significantly increased two days after the second MRT irradiation, indicating that alleviated melanoma growth and progression in animals treated with two MRT fractions could be a consequence of increased recruitment of anti-tumor neutrophils and T cells.

Conclusions

Our study indicates the approach for an optimal MRT regimen. Alone or in combination with immunotherapy, MRT may be able to not only enhance the local and locoregional control, but also boost abscopal effects. Therefore, MRT may be able to decrease the incidence of metastatic disease, the most common cause of death, even after successful treatment of the primary tumor.

Background and Aims

Normal tissue preservation is the dose-limiting factor in clinical radiation therapy where late pathological changes, such as fibrosis, are the major normal tissue complications that dictate dose prescription. Microbeam radiation therapy (MRT) is a novel radiation modality that shows exceptional normal tissue sparing while delivering high-dose beamlets at ultra-high, FLASH dose rates from synchrotron sources. Explored primarily in the brain and skin, the tissue-sparing effects of MRT have never been investigated in the liver, the second most common site of metastasis and organ at risk for abdominal irradiations. We therefore investigated the effects liver exposure to FLASH MRT following irradiation of the lower right lung.

Methods

C57BL/6J mice were irradiated with two, cross-fired arrays of 50 µm wide microbeams spaced 400 µm apart with peak doses of 400 Gy (dose-rate 991.7 Gy/s). Livers were collected for histological analysis at 12, 24, and 48 hours and 6 months post-irradiation.

Results

Livers did not exhibit any signs of fibrosis 6 months after MRT. Investigation of cell death mechanisms revealed scarce apoptotic cells and the absence of necrosis at earlier time points. Within 48 hours, macrophages were organized into the beam path accompanied by infiltration of hematopoietic and immune cell populations.

Conclusions

We have demonstrated that radiation doses exceeding clinical thresholds can be delivered to the liver via a high dose-rate, spatially-fractionated MRT modality. The absence of pathological changes, such as fibrosis, in normal liver tissues at 6 months post-irradiation suggests that MRT could be used for the safe treatment of liver metastases and primary hepatocellular carcinomas.

Background and Aims

Synchrotron Microbeam Radiation Therapy (S-MRT) consists of Synchrotron X-rays fractionated into an array of quasi-parallel beamlets delivered in FLASH mode. S-MRT achieves excellent tumour control and normal tissue sparing. This study aimed to evaluate S-MRT efficacy in a preclinical mouse lung carcinoma model.

Methods

Lewis-lung carcinoma implanted C57BL/6J mice were treated with two cross-fired arrays of S-MRT or Synchrotron-Broad Beam (S-BB) at 11 days after implantation. An array composed of seventeen microbeams 50 µm wide, spaced 400 µm apart was employed. S-MRT peak-dose was 400 Gy with a valley-dose of 4.76 Gy (delivery 361 ms, dose-rate 991.7 Gy/s). S-BB delivered a homogeneous dose of 5.16 Gy (delivery 129 ms, dose-rate 37.0 Gy/s). In addition, mouse lungs without tumours were irradiated with S-MRT, and radiation-related effects were assessed up to 6 months post-treatment.

Results

Mice in the S-MRT group had notably smaller tumour volumes compared to the S-BB group however, there was no difference in animal survival. This was attributed to pulmonary oedema found around the S-MRT-treated tumours. A mild transient form of fluid effusion was also observed in the S-MRT-treated normal lungs. Six months after S-MRT, the lungs of healthy mice were completely absent of radiation-induced pulmonary fibrosis.

Conclusions

Our study indicates that FLASH S-MRT is a promising tool for treating mouse lung carcinoma, i.e. reducing tumour size compared to mice treated with FLASH S-BB and sparing healthy lung from pulmonary fibrosis. Future experiments should focus on optimizing S-MRT parameters to minimize pulmonary oedema and maximize its therapeutic ratio.

Background and Aims

Accurate methods for monitoring the efficacy of treatments are key in radiooncology, where the quest for imaging techniques providing in three-dimensions (3D) both high spatial and contrast resolutions is incessant. X-ray Phase Contrast-Computed Tomography (XPCI-CT) is here proposed as a label-free, full-organ, multi-scale and 3D approach to study irradiated tissues with high sensitivity.

The aim is to visualize and characterize the effects of FLASH irradiations using broad beam (BB) and spatially-fractionated microbeams (MRT) with ex-vivo XPCI-CT for virtual 3D histology.

Methods

We delivered X-ray BB and MRT on healthy lungs or on healthy and glioblastoma-bearing brains of Fisher rats; irradiations were performed at the ID17 station of the European Synchrotron Radiation Facility using a dose rate of ~14000 Gy/s. After sacrificing the animals, target organs were removed, fixed and imaged by XPCI-CT using voxel sizes down to 0.7³ µm³. Afterwards samples were analysed by histology, X-ray wide-angle scattering and fluorescence.

Results

XPCI-CT allowed the depiction of brain and lungs anatomical details down to the cellular level, the identification of tumour tissue, necrosis, calcifications and micrometric MRT-transections within brains and of radiation induced fibrosis in lungs. BB irradiations produced the largest amount of fibrotic tissue while MRT caused isolated scars with small iron accumulations and calcium deposits in damaged blood vessels. A complementary structural/chemical characterization of the detected structures was also achieved.

Conclusions

The proposed approach provides a supportive technique for 3D imaging-based virtual histology and for an accurate description of post-treatment conditions of biological tissues supplementing the capabilities of standard lab-based techniques.