Validation of a Monte Carlo simulation for Microbeam Radiation Therapy on the Imaging and Medical Beamline at the Australian Synchrotron

Microbeam Radiation Therapy (MRT) is an emerging cancer treatment modality characterised by the use of high-intensity synchrotron-generated x-rays, spatially fractionated by a multi-slit collimator (MSC), to ablate target tumours. The implementation of an accurate treatment planning system, coupled with simulation tools that allow for independent verification of calculated dose distributions are required to ensure optimal treatment outcomes via reliable dose delivery. In this article we present data from the first Geant4 Monte Carlo radiation transport model of the Imaging and Medical Beamline at the Australian Synchrotron. We have developed the model for use as an independent verification tool for experiments in one of three MRT delivery rooms and therefore compare simulation results with equivalent experimental data. The normalised x-ray spectra produced by the Geant4 model and a previously validated analytical model, SPEC, showed very good agreement using wiggler magnetic field strengths of 2 and 3 T. However, the validity of absolute photon flux at the plane of the Phase Space File (PSF) for a fixed number of simulated electrons was unable to be established. This work shows a possible limitation of the G4SynchrotronRadiation process to model synchrotron radiation when using a variable magnetic field. To account for this limitation, experimentally derived normalisation factors for each wiggler field strength determined under reference conditions were implemented. Experimentally measured broadbeam and microbeam dose distributions within a Gammex RMI457 Solid Water® phantom were compared to simulated distributions generated by the Geant4 model. Simulated and measured broadbeam dose distributions agreed within 3% for all investigated configurations and measured depths. Agreement between the simulated and measured microbeam dose distributions agreed within 5% for all investigated configurations and measured depths

Establishment of novel long-term cultures from EpCAM positive and negative circulating tumour cells from patients with metastatic gastroesophageal cancer

Circulating tumour cell (CTC) enumeration and profiling has been established as a valuable clinical tool in many solid malignancies. A key challenge in CTC research is the limited number of cells available for study. Ex vivo CTC culture permits expansion of these rare cell populations for detailed characterisation, functional assays including drug sensitivity testing, and investigation of the pathobiology of metastases. We report for the first time the establishment and characterisation of two continuous CTC lines from patients with gastroesophageal cancer. The two cell lines (designated UWG01CTC and UWG02CTC) demonstrated rapid tumorigenic growth in immunodeficient mice and exhibit distinct genotypic and phenotypic profiles which are consistent with the tumours of origin. UWG02CTC exhibits an EpCAM+, cytokeratin+, CD44+ phenotype, while UWG01CTC, which was derived from a patient with metastatic neuroendocrine cancer, displays an EpCAM−, weak cytokeratin phenotype, with strong expression of neuroendocrine markers. Further, the two cell lines show distinct differences in drug and radiation sensitivity which match differential cancer-associated gene expression pathways. This is strong evidence implicating EpCAM negative CTCs in metastasis. These novel, well characterised, long-term CTC cell lines from gastroesophageal cancer will facilitate ongoing research into metastasis and the discovery of therapeutic targets

In vitro investigation of the dose-rate effect on the biological effectiveness of megavoltage X-ray radiation doses

Radiation therapy is rapidly evolving toward the delivery of higher dose rates to improve cancer treatment. In vitro experiments were performed to investigate the response of 9L and MCF-7 cancer cell lines, exposed to 10 MV X-ray radiations. Up to 8 Gy was delivered at a dose-rate of 50 cGy/min compared to 5 Gy/min. The data obtained emphasizes the importance of taking into account not only the physical, but also the radiobiological parameters, when planning a particular cancer treatment

First in vitro evidence of modulated electro-hyperthermia treatment performance in combination with megavoltage radiation by clonogenic assay

Modulated electro-hyperthermia (mEHT) is a form of hyperthermia used in the treatment of cancer. It is a variation that relies on a particular form of enhanced selectivity to enable more effective cancerous cell death yet maintaining the integrity of healthy non-cancerous cells. It is yet to successfully make the major step into the wider medical community despite several encouraging trials. In this study, we investigate mEHT from an in vitro perspective. We demonstrate a supra-additive effect on 9 L gliosarcoma cells when exposed to mEHT in combination with MV X-ray radiation. The supra-additive effect is hypothesized to be induced by the mEHT mechanism that in turn causes apoptosis, membrane damage and an increase in rate of cell growth. This proves to be extremely advantageous in the case of the aggressive 9 L cell line as it is known to be radioresistant. However, the universal success of this multimodal treatment does not appear to be positive for all cell lines and requires further research. Due to the fundamental approach taken in this research, our results also provide a new prospect for mEHT to be a tool for sterilizing otherwise radioresistant cancers

Indirect radio-chemo-beta therapy: a targeted approach to increase biological efficiency of x-rays based on energy

Despite the use of multimodal treatments incorporating surgery, chemotherapy and radiotherapy, local control of gliomas remains a major challenge. The potential of a new treatment approach called indirect radio-chemo-beta therapy using the synergy created by combining methotrexate (MTX) with bromodeoxyuridine (BrUdR) under optimum energy x-ray irradiation is assessed. 9L rat gliosarcoma cells pre-treated with 0.01 μM MTX and/or 10 μM BrUdR were irradiated in vitro with 50 kVp, 125 kVp, 250 kVp, 6 MV and 10 MV x-rays. The cytotoxicity was assessed using clonogenic survival as the radiobiological endpoint. The photon energy with maximum effect was determined using radiation sensitization enhancement factors at 10% clonogenic survival (SER10%). The cell cycle distribution was investigated using flow cytometric analysis with propidium iodide staining. Incorporation of BrUdR in the DNA was detected by the fluorescence of labelled anti-BrUdR antibodies. The radiation sensitization enhancement exhibits energy dependence with a maximum of 2.3 at 125 kVp for the combined drug treated cells. At this energy, the shape of the clonogenic survival curve of the pharmacological agents treated cells changes substantially. This change is interpreted as an increased lethality of the local radiation environment and is attributed to supplemented inhibition of DNA repair. Radiation induced chemo-beta therapy was demonstrated in vitro by the targeted activation of combined pharmacological agents with optimized energy tuning of x-ray beams on 9 L cells. Our results show that this is a highly effective form of chemo-radiation therapy

Cerium oxide nanoparticles: influence of the high-Z component revealed on radioresistant 9L cell survival under X-ray irradiation

This article pioneers a study into the influence of the high-Z component of nanoparticles on the efficacy of radioprotection some nanoparticles offer to exposed cells irradiated with X-rays. We reveal a significant decrease in the radioprotection efficacy for cells exposed to CeO2 nanoparticles and irradiated with 10 MV and 150 kVp X-rays. In addition, analysis of the 150 kVp survival curve data indicates a change in radiation quality, becoming more lethal for irradiated cells exposed to CeO2 nanoparticles. We attribute the change in efficacy to an increase in high linear energy transfer Auger electron production at 150 kVp which counterbalances the CeO2 nanoparticle radioprotection capability and locally changes the radiation quality. This study highlights an interesting phenomenon that must be considered if radiation protection drugs for use in radiotherapy are developed based on CeO2 nanoparticles

Today\u27s monolithic silicon array detector for small field dosimetry: The Octa

The dosimetry of small photon beams is challenging due to detector position uncertainties, dose averaging and lack of electronic equilibrium. Currently only few, single detectors are suitable for measurements in this context, and none is ideal. This study reports on the dosimetric characterization of small fields collimated by fixed cones, performed by a novel 2D monolithic silicon array detector, the Octa

Synchrotron activation radiotherapy: Effects of dose-rate and energy spectra to tantalum oxide nanoparticles selective tumour cell radiosensitization enhancement

Synchrotron radiation is unique in its ability to deliver dose at high dose rates using kiloelectronvolt photons. We are investigating the use of Tantalum pentoxide (Ta2O5) nano-structured particles (NSPs) that are to date unexplored in synchrotron radiation fields as they have high atomic number (Z=73) are biocompatible and are therefore potential radio sensitizers. We exposed cell culture flasks containing 9L gliosarcoma tumour cells or Madin-Darby Canine Kidney (MDCK) non-tumour cells to the NSPs and treated the cells using a broad synchrotron beam (140 keV median energy; average dose rate of 50 Gy/s) at the Australian Synchrotron. We compare the results with those from similar cells treated using a conventional 150 kVp orthovoltage field (dose rate of 0.0127 Gy/s). The results reveal that the high dose-rate synchrotron irradiation is more effective at killing the 9L cells relative to the MDCK cells than the orthovoltage irradiation. On the other hand, the NSPs are more effective at radiosensitizing the 9L cells compared to the MDCK cells in the orthovoltage radiation field, which is due to the NSP energy dependence in the kilovoltage energy range. Both the dose rate and energy spectrum need to be considered in future studies with synchrotron activation radiotherapy (SART)

Nanostructures, concentrations and energies: an ideal equation to extend therapeutic efficiency on radioresistant 9L tumour cells using Ta2O5 ceramic nanostructured particles

This work presents an in-depth analysis into the dependencies of radiosensitisation on X-ray beam energy, particle morphology and particle concentration for Ta2O5 nanostructured particles. A maximum sensitisation enhancement ratio of 1.46 was attained with irradiation of a 10 MV x-ray photon beam on 9L cells exposed to the less aggregated form of NSPs at 500 μg/mL-1. A significant increase in sensitisation of 30% was noted at 150 kVp for irradiation of the less aggregated form of tantalum pentoxide NSPs compared to its more agglomerated counterpart. Interestingly, no differences in sensitisation were observed between 50 and 500 μg/mL-1 for all beam energies and NSPs tested. This is explained by a physical shell effect , where by the NSPs form layers around the cells (observed using confocal microscopy), with the inner layers contributing to enhancement, while the outer layers shield the cell from damage

Radiosensitisation enhancement effect of BrUdR and Ta2O5 NSPs in combination with 5-Fluorouracil antimetabolite in kilovoltage and megavoltage radiation

This article demonstrates in vitro a synergistic effect on 9L gliosarcoma cells when exposed to bromodeoxyuridine (BrUdR) and a low concentration (100 times lower than the IC50) of 5-Fluorouracil (5-FU), in combination with x-ray irradiation. The synergy is brought about by several important factors including the x-ray beam energy, atomic number of the BrUdR (Z = 35), effectiveness of 5-FU in reducing the available repair processes and distribution of the BrUdR in and around the 9L cells (32% of the total substitution of BrUdR for thymidine into nucleus DNA). Our results show that the synergistic effect, evident in an optimised 125 kVp x-ray field, leads to a radiosensitisation enhancement ratio at the 10% survival level (SER10%) of 2.11. We highlight the importance of the aforementioned factors by similarly performed experiments for higher Z (Z = 73) tantalum pentoxide nano-structured particles (Ta2O5 NSPs) that are substituted for the BrUdR in larger concentration (~10 times). In the Ta2O5 NSPs experiments, no synergistic effect is observed in the kVp irradiation with optimal energy spectrum even though the effective Z and NSP concentration is much higher than for BrUdR. All experiments were repeated using a MV x-ray irradiation field and no synergistic effect is observed for either the BrUdR or Ta2O5 case. We therefore hypothesise that the synergistic outcome is due to more drastic and complex damages induced by BrUdR under the exposure of kVp radiation. Such damages are achieved by the localisation of the BrUdR in the DNA and the high LET (very short range) secondary electrons in combination with the 5-FU. In order to achieve similar synergistic effects in the more clinically relevant x-ray energy field the concentration of the high Z material needs to be greater in order to create a higher LET electron environment