Evolution of the Supermodel: Progress in Modelling Radiotherapy Response in Mice

Radiotherapy protocols for mouse cancer model

Radiotherapy is a crucial treatment modality for cancer patients, with approximately 60% of individuals undergoing ionizing radiation as part of their disease management. In recent years, there has been a growing trend toward minimizing irradiation fields through the use of image-guided dosimetry and innovative technologies. These advancements allow for selective irradiation, delivering higher local doses while reducing the number of treatment sessions. Consequently, computer-assisted methods have significantly enhanced the effectiveness of radiotherapy in the curative and palliative treatment of various cancers. Although radiation therapy alone can effectively achieve local control in some cancer types, it may not be sufficient for others. As a result, further preclinical research is necessary to explore novel approaches including new schedules of radiotherapy treatments. Unfortunately, there is a concerning lack of correlation between clinical outcomes and experiments conducted on mouse models. We hypothesize that this disparity arises from the differences in irradiation strategies employed in preclinical studies compared to those used in clinical practice, which ultimately affects the translatability of findings to patients. In this study, we present two comprehensive radiotherapy protocols for the treatment of orthotopic melanoma and glioblastoma tumors. These protocols utilize a small animal radiation research platform, which is an ideal radiation device for delivering localized and precise X-ray doses to the tumor mass. By employing these platforms, we aim to limit the side effects associated with irradiating healthy surrounding tissues. Our detailed protocols offer a valuable framework for conducting preclinical studies that closely mimic clinical radiotherapy techniques, bridging the gap between experimental results and patient outcomes.

From pre-clinical to translational brain metastasis research: current challenges and emerging opportunities

Brain metastasis, characterized by poor clinical outcomes, is a devastating disease. Despite significant mechanistic and therapeutic advances in recent years, pivotal improvements in clinical interventions have remained elusive. The heterogeneous nature of the primary tumor of origin, complications in drug delivery across the blood-brain barrier, and the distinct microenvironment collectively pose formidable clinical challenges in developing new treatments for patients with brain metastasis. Although current preclinical models have deepened our basic understanding of the disease, much of the existing research on brain metastasis has employed a reductionist approach. This approach, which often relies on either in vitro systems or in vivo injection models in young and treatment-naive mouse models, does not give sufficient consideration to the clinical context. Given the translational importance of brain metastasis research, we advocate for the design of preclinical experimental models that take into account these unique clinical challenges and align more closely with current clinical practices. We anticipate that aligning and simulating real-world patient conditions will facilitate the development of more translatable treatment regimens. This brief review outlines the most pressing clinical challenges, the current state of research in addressing them, and offers perspectives on innovative metastasis models and tools aimed at identifying novel strategies for more effective management of clinical brain metastasis.

Characterisation of quantitative imaging biomarkers for inflammatory and fibrotic radiation-induced lung injuries using preclinical radiomics

BACKGROUND AND PURPOSE

Radiomics is a rapidly evolving area of research that uses medical images to develop prognostic and predictive imaging biomarkers. In this study, we aimed to identify radiomics features correlated with longitudinal biomarkers in preclinical models of acute inflammatory and late fibrotic phenotypes following irradiation.

MATERIALS AND METHODS

Female C3H/HeN and C57BL6 mice were irradiated with 20 Gy targeting the upper lobe of the right lung under cone-beam computed tomography (CBCT) image-guidance. Blood samples and lung tissue were collected at baseline, weeks 1, 10 & 30 to assess changes in serum cytokines and histological biomarkers. The right lung was segmented on longitudinal CBCT scans using ITK-SNAP. Unfiltered and filtered (wavelet) radiomics features (n = 842) were extracted using PyRadiomics. Longitudinal changes were assessed by delta analysis and principal component analysis (PCA) was used to remove redundancy and identify clustering. Prediction of acute (week 1) and late responses (weeks 20 & 30) was performed through deep learning using the Random Forest Classifier (RFC) model.

RESULTS

Radiomics features were identified that correlated with inflammatory and fibrotic phenotypes. Predictive features for fibrosis were detected from PCA at 10 weeks yet overt tissue density was not detectable until 30 weeks. RFC prediction models trained on 5 features were created for inflammation (AUC 0.88), early-detection of fibrosis (AUC 0.79) and established fibrosis (AUC 0.96).

CONCLUSIONS

This study demonstrates the application of deep learning radiomics to establish predictive models of acute and late lung injury. This approach supports the wider application of radiomics as a non-invasive tool for detection of radiation-induced lung complications.

Post-Implantation Inflammatory Responses to Xenogeneic Tissue-Engineered Cartilage Implanted in Rabbit Trachea: The Role of Cultured Chondrocytes in the Modification of Inflammation

Immune responses to tissue-engineered grafts made of xenogeneic materials remain poorly studied. The scope of current investigations is limited by the lack of information on orthotopically implanted grafts. A deeper understanding of these processes is of great importance since innovative surgical approaches include the implantation of xenogeneic decellularized scaffolds seeded by cells. The purpose of our work is to study the immunological features of tracheal repair during the implantation of tissue-engineered constructs based on human xenogeneic scaffolds modified via laser radiation in rabbits. The samples were stained with hematoxylin and Safranin O, and they were immunostained with antibodies against tryptase, collagen II, vimentin, and CD34. Immunological and inflammatory responses were studied by counting immune cells and evaluating blood vessels and collagen. Leukocyte-based inflammation prevailed during the implantation of decellularized unseeded scaffolds; meanwhile, plasma cells were significantly more abundant in tissue-engineered constructs. Mast cells were insignificantly more abundant in tissue-engineered construct samples. Conclusions: The seeding of decellularized xenogeneic cartilage with chondrocytes resulted in a change in immunological reactions upon implantation, and it was associated with plasma cell infiltration. Tissue-engineered grafts widely differed in design, including the type of used cells. The question of immunological response depending on the tissue-engineered graft composition requires further investigation.

Dosimetry for radiobiologicalin vivoexperiments at laser plasma-based proton accelerators

Objective.Laser plasma-based accelerators (LPAs) of protons can contribute to research of ultra-high dose rate radiobiology as they provide pulse dose rates unprecedented at medical proton sources. Yet, LPAs pose challenges regarding precise and accurate dosimetry due to the high pulse dose rates, but also due to the sources' lower spectral stability and pulsed operation mode. Forin vivomodels, further challenges arise from the necessary small field dosimetry for volumetric dose distributions. For these novel source parameters and intended applications, a dosimetric standard needs to be established.Approach.In this work, we present a dosimetry and beam monitoring framework forin vivoirradiations of small target volumes with LPA protons, solving aforementioned challenges. The volumetric dose distribution in a sample (mean dose value and lateral/depth dose inhomogeneity) is provided by combining two independent dose measurements using radiochromic films (dose rate-independent) and ionization chambers (dose rate-dependent), respectively. The unique feature of the dosimetric setup is beam monitoring with a transmission time-of-flight spectrometer to quantify spectral fluctuations of the irradiating proton pulses. The resulting changes in the depth dose profile during irradiation of anin vivosample are hence accessible and enable pulse-resolved depth dose correction for each dose measurement.Main results.A first successful small animal pilot study using an LPA proton source serves as a testcase for the presented dosimetry approach and proves its performance in a realistic setting.Significance.With several facilities worldwide either setting up or already using LPA infrastructure for radiobiological studies with protons, the importance of LPA-adapted dosimetric frameworks as presented in this work is clearly underlined.

Feasibility and guidelines for the use of an injectable fiducial marker (BioXmark ®) to improve target delineation in preclinical radiotherapy studies using mouse models

BACKGROUND

Preclinical models of radiotherapy (RT) response are vital for the continued success and evolution of RT in the treatment of cancer. The irradiation of tissues in mouse models necessitates high levels of precision and accuracy to recapitulate clinical exposures and limit adverse effects on animal welfare. This requirement has been met by technological advances in preclinical RT platforms established over the past decade. Small animal RT systems use onboard computed tomography (CT) imaging to delineate target volumes and have significantly refined radiobiology experiments with major 3Rs impacts. However, the CT imaging is limited by the differential attenuation of tissues resulting in poor contrast in soft tissues. Clinically, radio-opaque fiducial markers (FMs) are used to establish anatomical reference points during treatment planning to ensure accuracy beam targeting, this approach is yet to translate back preclinical models.

METHODS

We report on the use of a novel liquid FM BioXmark ® developed by Nanovi A/S (Kongens Lyngby, Denmark) that can be used to improve the visualisation of soft tissue targets during beam targeting and minimise dose to surrounding organs at risk. We present descriptive protocols and methods for the use of BioXmark ® in experimental male and female C57BL/6J mouse models.

RESULTS

These guidelines outline the optimum needle size for uptake (18-gauge) and injection (25- or 26-gauge) of BioXmark ® for use in mouse models along with recommended injection volumes (10-20 µl) for visualisation on preclinical cone beam CT (CBCT) scans. Injection techniques include subcutaneous, intraperitoneal, intra-tumoral and prostate injections.

CONCLUSIONS

The use of BioXmark ® can help to standardise targeting methods, improve alignment in preclinical image-guided RT and significantly improve the welfare of experimental animals with the reduction of normal tissue exposure to RT.

Assessment of Variabilities in Lung-Contouring Methods on CBCT Preclinical Radiomics Outputs

Simple Summary

This study is the first to evaluate the impact of contouring differences on radiomics analysis in preclinical CBCT scans. We found that the variation in quantitative image readouts was greater between segmentation tools than between observers.

Abstract

Radiomics image analysis has the potential to uncover disease characteristics for the development of predictive signatures and personalised radiotherapy treatment. Inter-observer and inter-software delineation variabilities are known to have downstream effects on radiomics features, reducing the reliability of the analysis. The purpose of this study was to investigate the impact of these variabilities on radiomics outputs from preclinical cone-beam computed tomography (CBCT) scans. Inter-observer variabilities were assessed using manual and semi-automated contours of mouse lungs (n = 16). Inter-software variabilities were determined between two tools (3D Slicer and ITK-SNAP). The contours were compared using Dice similarity coefficient (DSC) scores and the 95th percentile of the Hausdorff distance (HD_95p) metrics. The good reliability of the radiomics outputs was defined using intraclass correlation coefficients (ICC) and their 95% confidence intervals. The median DSC scores were high (0.82–0.94), and the HD_95p metrics were within the submillimetre range for all comparisons. the shape and NGTDM features were impacted the most. Manual contours had the most reliable features (73%), followed by semi-automated (66%) and inter-software (51%) variabilities. From a total of 842 features, 314 robust features overlapped across all contouring methodologies. In addition, our results have a 70% overlap with features identified from clinical inter-observer studies.

Development and optimisation of a preclinical cone beam computed tomography-based radiomics workflow for radiation oncology research

Background and purpose

Radiomics features derived from medical images have the potential to act as imaging biomarkers to improve diagnosis and predict treatment response in oncology. However, the complex relationships between radiomics features and the biological characteristics of tumours are yet to be fully determined. In this study, we developed a preclinical cone beam computed tomography (CBCT) radiomics workflow with the aim to use in vivo models to further develop radiomics signatures.

Materials and methods

CBCT scans of a mouse phantom were acquired using onboard imaging from a small animal radiotherapy research platform (SARRP, Xstrahl). The repeatability and reproducibility of radiomics outputs were compared across different imaging protocols, segmentation sizes, pre-processing parameters and materials. Robust features were identified and used to compare scans of two xenograft mouse tumour models (A549 and H460).

Results

Changes to the radiomics workflow significantly impact feature robustness. Preclinical CBCT radiomics analysis is feasible with 119 stable features identified from scans imaged at 60 kV, 25 bin width and 0.26 mm slice thickness. Large variation in segmentation volumes reduced the number of reliable radiomics features for analysis. Standardization in imaging and analysis parameters is essential in preclinical radiomics analysis to improve accuracy of outputs, leading to more consistent and reproducible findings.

Conclusions

We present the first optimised workflow for preclinical CBCT radiomics to identify imaging biomarkers. Preclinical radiomics has the potential to maximise the quantity of data captured in in vivo experiments and could provide key information supporting the wider application of radiomics.

Roadmap for precision preclinical x-ray radiation studies

This Roadmap paper covers the field of precision preclinical x-ray radiation studies in animal models. It is mostly focused on models for cancer and normal tissue response to radiation, but also discusses other disease models. The recent technological evolution in imaging, irradiation, dosimetry and monitoring that have empowered these kinds of studies is discussed, and many developments in the near future are outlined. Finally, clinical translation and reverse translation are discussed.

Findings from international archived data: Fractionation reduces mortality risk of ionizing radiation for total doses below 4 Gray in rodents

Ionizing radiation is omnipresent and unavoidable on Earth; nevertheless, the range of doses and modes of radiation delivery that represent health risks remain controversial. Radiation protection policy for civilians in US is set at 1 mSv per year. Average persons from contemporary populations are exposed to several hundred milliSieverts (mSv) over their lifetimes from both natural and human made sources such as radon, cosmic rays, CT-scans (20-50 mSv partial body exposure per scan), etc. Health risks associated with these and larger exposures are focus of many epidemiological studies, but uncertainties of these estimates coupled with individual and environmental variation make it is prudent to attempt to use animal models and tightly controlled experimental conditions to supplement our evaluation of radiation risk question. Data on 11,528 of rodents of both genders exposed to x-ray or gamma-ray radiation in facilities in US and Europe were used for this analysis; animal mortality data argue that fractionated radiation exposures have about 2 fold less risk per Gray than acute radiation exposures in the range of doses between 0.25 and 4 Gy.

Murine models of radiation cardiotoxicity: A systematic review and recommendations for future studies

BACKGROUND AND PURPOSE

The effects of radiation on the heart are dependent on dose, fractionation, overall treatment time, and pre-existing cardiovascular pathology. Murine models have played a central role in improving our understanding of the radiation response of the heart yet a wide range of exposure parameters have been used. We evaluated the study design of published murine cardiac irradiation experiments to assess gaps in the literature and to suggest guidance for the harmonisation of future study reporting.

METHODS AND MATERIALS

A systematic review of mouse/rat studies published 1981-2021 that examined the effect of radiation on the heart was performed. The protocol was published on PROSPERO (CRD42021238921) and the findings were reported in accordance with the PRISMA guidance. Risk of bias was assessed using the SYRCLE checklist.

RESULTS

159 relevant full-text original articles were reviewed. The heart only was the target volume in 67% of the studies and simulation details were unavailable for 44% studies. Dosimetry methods were reported in 31% studies. The pulmonary effects of whole and partial heart irradiation were reported in 13% studies. Seventy-eight unique dose-fractionation schedules were evaluated. Large heterogeneity was observed in the endpoints measured, and the reporting standards were highly variable.

CONCLUSIONS

Current murine models of radiation cardiotoxicity cover a wide range of irradiation configurations and latency periods. There is a lack of evidence describing clinically relevant dose-fractionations, circulating biomarkers and radioprotectants. Recommendations for the consistent reporting of methods and results of in vivo cardiac irradiation studies are made to increase their suitability for informing the design of clinical studies.

A scoping review of small animal image-guided radiotherapy research: Advances, impact and future opportunities in translational radiobiology

Background and purpose

To provide a scoping review of published studies using small animal irradiators and highlight the progress in preclinical radiotherapy (RT) studies enabled by these platforms since their development and commercialization in 2007.

Materials and methods

PubMed searches and manufacturer records were used to identify 907 studies that were screened with 359 small animal RT studies included in the analyses. These articles were classified as biology or physics contributions and into subgroups based on research aims, experimental models and other parameters to identify trends in the preclinical RT research landscape.

Results

From 2007 to 2021, most published articles were biology contributions (62%) whilst physics contributions accounted for 38% of the publications. The main research areas of physics articles were in dosimetry and calibration (24%), treatment planning and simulation (22%), and imaging (22%) and the studies predominantly used phantoms (41%) or in vivo models (34%). The majority of biology contributions were tumor studies (69%) with brain being the most commonly investigated site. The most frequently investigated areas of tumor biology were evaluating radiosensitizers (33%), model development (30%) and imaging (21%) with cell-line derived xenografts the most common model (82%). 31% of studies focused on normal tissue radiobiology and the lung was the most investigated site.

Conclusions

This study captures the trends in preclinical RT research using small animal irradiators from 2007 to 2021. Our data show the increased uptake and outputs from preclinical RT studies in important areas of biology and physics research that could inform translation to clinical trials.

Aging preclinical models in oncology field: from cells to aging

Aging is a universal complex and multifactorial physiological process that leads to the increasing incidence of various diseases including cancer. Indeed, 40% of individuals aged 65 years and over will have newly diagnosed cancers. Although most treated patients are elderly people, a low inclusion of the geriatric population is observed in most clinical trials. Furthermore, lethal side effects of antineoplastic therapy are markedly exacerbated with aging. Most cancer therapies were validated on young mice models, complicating results transposition to elderly patients. Thus, understanding the role of aging in tumor progression and response to cancer therapies with accurate preclinical models must be investigated. Therefore, this review aimed to summarize the state of the literature about preclinical models used to investigate the impact of aging microenvironment on tumorigenic potential, and on antineoplastic therapy response. Despite the advances in technology, and the increasing incidence of cancer in the elderly population, this present review focuses on the few studies using preclinical tumor model of aging. Since the biology of aging is challenging, aging animal models are an inevitable prelude. New emerging tools such as human organoid offer a promising path in research dedicated to aging.

Radiobiology of the FLASH effect

Radiation exposures at ultrahigh dose rates (UHDRs) at several orders of magnitude greater than in current clinical radiotherapy (RT) have been shown to manifest differential radiobiological responses compared to conventional (CONV) dose rates. This has led to studies investigating the application of UHDR for therapeutic advantage (FLASH-RT) that have gained significant interest since the initial discovery in 2014 that demonstrated reduced lung toxicity with equivalent levels of tumor control compared with conventional dose-rate RT. Many subsequent studies have demonstrated the potential protective role of FLASH-RT in normal tissues, yet the underlying molecular and cellular mechanisms of the FLASH effect remain to be fully elucidated. Here, we summarize the current evidence of the FLASH effect and review FLASH-RT studies performed in preclinical models of normal tissue response. To critically examine the underlying biological mechanisms of responses to UHDR radiation exposures, we evaluate in vitro studies performed with normal and tumor cells. Differential responses to UHDR versus CONV irradiation recurrently involve reduced inflammatory processes and differential expression of pro- and anti-inflammatory genes. In addition, frequently reduced levels of DNA damage or misrepair products are seen after UHDR irradiation. So far, it is not clear what signal elicits these differential responses, but there are indications for involvement of reactive species. Different susceptibility to FLASH effects observed between normal and tumor cells may result from altered metabolic and detoxification pathways and/or repair pathways used by tumor cells. We summarize the current theories that may explain the FLASH effect and highlight important research questions that are key to a better mechanistic understanding and, thus, the future implementation of FLASH-RT in the clinic.

Real-World Analysis of the Impact of Radiotherapy on Immunotherapy Efficacy in Non-Small Cell Lung Cancer

BACKGROUND

Immunotherapy (IO) provides a significant benefit for a subgroup of non-small cell lung cancer (NSCLC) patients. Radiotherapy (XRT) might enhance the efficacy of IO. We evaluated the impact of the specifics of XRT treatments on the OS of IO-treated NSCLC patients.

METHODS

Metastatic NSCLC patients treated with IO were retrospectively identified. Parameters included demographics, tumor characteristics, IO and XRT details. Correlation between the parameters and OS was tested with Cox regression.

RESULTS

453 patients were included. No XRT was given to 167 (36.9%) patients, whereas XRT prior and after IO had 182 (40.2%) and 104 (22.9%) patients, respectively. XRT total doses between 30 and 40 Gy had better overall survival (OS) compared to non-irradiated patients (hazard ratio (HR) 0.5, 95% CI 0.25-1.0, p = 0.049). Worse outcome was seen with total doses ≤ 10 Gy (HR 1.67, 95% 1.13-2.5, p = 0.01), XRT fractions of 4.1-8 Gy (HR 1.48, 95% CI 1.05-2.1, p = 0.027) and XRT to the bone (HR 1.36, 95% CI 1.01-1.8, p = 0.04). Several clinical parameters correlated with OS in the univariate analysis of the IO-treated patients. While, in the multivariate analysis, only ECOG-PS, treatment line, type of IO, albumin and NLR remained statistically significant.

CONCLUSION

Specific doses, fractions and sites of XRT correlated with the OS of IO-treated NSCLC patients in the univariate analysis, although not in the multivariate analysis.

Radiation therapy and molecular-targeted agents in preclinical testing for immunotherapy, brain tumors, and sarcomas: Opportunities and challenges

Despite radiation therapy (RT) being an integral part of the treatment of most pediatric cancers and the recent discovery of novel molecular-targeted agents (MTAs) in this era of precision medicine with the potential to improve the therapeutic ratio of modern chemoradiotherapy regimens, there are only a few preclinical trials being conducted to discover novel radiosensitizers and radioprotectors. This has resulted in a paucity of translational clinical trials combining RT and novel MTAs. This report describes the opportunities and challenges of investigating RT together with MTAs in preclinical testing for immunotherapy, brain tumors, and sarcomas in pediatric oncology. We discuss the need for improving the collaboration between radiation oncologists, biologists, and physicists to improve the reliability, reproducibility, and translational potential of RT-based preclinical research. Current translational clinical trials using RT and MTAs for immunotherapy, brain tumors, and sarcomas are described. The technologic advances in experimental RT, availability of novel experimental tumor models, advances in immunology and tumor biology, and the discovery of novel MTAs together hold considerable promise for good quality preclinical and clinical multimodality research to improve the current rates of survival and toxicity in children afflicted with cancer.

Cardiac sub-volume targeting demonstrates regional radiosensitivity in the mouse heart

BACKGROUND AND PURPOSE

Radiation-induced cardiac toxicity (RICT) remains one of the most critical dose limiting constraints in radiotherapy. Recent studies have shown higher doses to the base of the heart are associated with worse overall survival in lung cancer patients receiving radiotherapy. This work aimed to investigate the impact of sub-volume heart irradiation in a mouse model using small animal image-guided radiotherapy.

MATERIALS AND METHODS

C57BL/6 mice were irradiated with a single fraction of 16 Gy to the base, middle or apex of the heart using a small animal radiotherapy research platform. Cone beam CT and echocardiography were performed at baseline and at 10 week intervals until 50 weeks post-treatment. Structural and functional parameters were correlated with mean heart dose (MHD) and volume of heart receiving 5 Gy (V5).

RESULTS

All irradiated mice showed a time dependent increase in left ventricle wall thickness in diastole of ~0.2 mm detected at 10 weeks post-treatment, with the most significant and persistent changes occurring in the heart base-irradiated animals. Similarly, statistically different functional effects (p < 0.01) were observed in base-irradiated animals which showed the most significant decreases compared to controls. The observed functional changes did not correlate with MHD and V5 (R2 < 0.1), indicating that whole heart dosimetry parameters do not predict physiological changes resulting from cardiac sub-volume irradiation.

CONCLUSIONS

This is the first report demonstrating the structural and functional consequences of sub-volume targeting in the mouse heart and reverse translates clinical observations indicating the heart base as a critical radiosensitive region.

Roadmap for metal nanoparticles in radiation therapy: current status, translational challenges, and future directions

This roadmap outlines the potential roles of metallic nanoparticles (MNPs) in the field of radiation therapy. MNPs made up of a wide range of materials (from Titanium, Z = 22, to Bismuth, Z = 83) and a similarly wide spectrum of potential clinical applications, including diagnostic, therapeutic (radiation dose enhancers, hyperthermia inducers, drug delivery vehicles, vaccine adjuvants, photosensitizers, enhancers of immunotherapy) and theranostic (combining both diagnostic and therapeutic), are being fabricated and evaluated. This roadmap covers contributions from experts in these topics summarizing their view of the current status and challenges, as well as expected advancements in technology to address these challenges.

Evaluation of a Novel Liquid Fiducial Marker, BioXmark®, for Small Animal Image-Guided Radiotherapy Applications

BioXmark^® (Nanovi A/S, Denmark) is a novel fiducial marker based on a liquid, iodine-based and non-metallic formulation. BioXmark^® has been clinically validated and reverse translated to preclinical models to improve cone-beam CT (CBCT) target delineation in small animal image-guided radiotherapy (SAIGRT). However, in phantom image analysis and in vivo evaluation of radiobiological response after the injection of BioXmark^® are yet to be reported. In phantom measurements were performed to compare CBCT imaging artefacts with solid fiducials and determine optimum imaging parameters for BioXmark^®. In vivo stability of BioXmark^® was assessed over a 5-month period, and the impact of BioXmark^® on in vivo tumour response from single-fraction and fractionated X-ray exposures was investigated in a subcutaneous syngeneic tumour model. BioXmark^® was stable, well tolerated and detectable on CBCT at volumes ≤10 µL. Our data showed imaging artefacts reduced by up to 84% and 89% compared to polymer and gold fiducial markers, respectively. BioXmark^® was shown to have no significant impact on tumour growth in control animals, but changes were observed in irradiated animals injected with BioXmark^® due to alterations in dose calculations induced by the sharp contrast enhancement. BioXmark^® is superior to solid fiducials with reduced imaging artefacts on CBCT. With minimal impact on the tumour growth delay, BioXmark^® can be implemented in SAIGRT to improve target delineation and reduce set-up errors.