Small Animal Tumor Research Articles

The relevance of the treatment of lung tumors in small domestic animals and the prospects for the use of targeted therapy for EGFR and ALK/ROS1 mutations on the example of clinical data from humane and veterinary medicine

In the period from 2020 to 2023 was conducted a retrospective study of animal disease histories with lung neoplasia. 43 animals (15 dogs and 28 cats) were included in the study. Neoplasms were identified by instrumental and histopathological methods. Malignant lung tumors have different histological structure, differ in clinical course and treatment results. Surgery is the method of choice for dogs and cats with primary lung tumors. In humans, the surgical method is one of the main methods of treating lung cancer (LC). Since in 70% of cases LC develops without clinical signs, most cases of the trachea, bronchi and lung tumors are detected at IV stage not only in animals, but also in humans, which makes radical surgery impossible. The development of molecular biology methods leads to the development of new treatment methods based on the use of more effective antitumor drugs. One of the innovative methods of cancer treatment is targeted therapy. Molecular-oriented drugs block the growth of cancer cells by interfering with the mechanism of action of specific target molecules necessary for carcinogenesis and tumor growth. In veterinary medicine, surgical and chemotherapeutic methods of treatment are mainly used, while the latter does not show sufficient effectiveness. At the same time, in humane medicine for the treatment of lung cancer widely use targeted therapy, the effect of which is more accurate and effective. There is not much information in the available literature on the use of targeted therapy in animals and there are practically no studies on the treatment of inoperable LC in cats, which makes it relevant to conduct clinical studies on the use of targeted drugs in companion animals.

Abstract 487: Peptide amphiphiles hitchhike on endogenous biomolecules for enhanced drug delivery

Abstract Peptide amphiphiles (PAs) have been applied as building blocks for self-assembled nanostructures with various morphologies. These self-assembled nanostructures are promising drug delivery platforms as they are naturally biodegradable and biocompatible with low immunogenicity. One primary focus in drug delivery using the PA nanostructures has been to develop strongly assembled structures to avoid disassembly in the blood and allow them to carry payloads to their intended targets. In this work, rather than developing stable self-assembled PA structures, we focused on weakly assembled PA nanostructures to investigate their interactions with blood components and to understand how these interactions affect their biodistribution. We found that weakly assembled PA nanostructures (SA-E) quickly disassembled in plasma and reassembled with lipoproteins (LPs), which significantly prolonged the blood circulation of SA-E in mice. We showed that SA-E crossed the endothelial barriers through transcytosis only when they were assembled with LPs. Cellular uptake studies showed that SA-E accumulated in cancer cells through lipid-raft-mediated uptake. Interestingly, their cellular internalization was independent of LP receptors, suggesting that SA-E assembles with different endogenous biomolecules in vivo. By exploiting these endogenous interactions, SA-E demonstrated high tumor accumulation in a myriad of small animal tumor models of breast, colon, pancreatic, brain, skin, prostate, or lung cancers. SA-E demonstrated large tumor-to-background signal ratios in live animals (>5), extended retention (>2 weeks), and excellent tissue distribution (tumor to liver signal >3) in these tumor models. Encouraged by the excellent tumor accumulation of SA-E, we prepared SA-E drug conjugate using a highly potent and toxic chemotherapeutic agent, Monomethyl auristatin E (MMAE). SA-E-MMAE conjugate demonstrated strong antitumor efficacy in aggressive breast and glioma models in mice with reduced side effects. With its simple and modular design and universal tumor accumulation mechanism, SA-E represents a promising platform for broad applications in cancer therapy. Citation Format: Jared M. Fischer, Morgan Stewart, Mingchong Dai, Samuel Drennan, Sinan Sabuncu, Benjamin Kingston, Isabel Dengos, Li Xiang, Karla Bonic, Xin Yi, Srivathsan Ranganathan, Bruce Branchaud, Adem Yildirim. Peptide amphiphiles hitchhike on endogenous biomolecules for enhanced drug delivery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 487.

Development of an integrated dual-modality 3D bioluminescence tomography and ultrasound imaging system for small animal tumor imaging.

Ultrasound (US) is a valuable tool for imaging soft tissue and visualizing tumor contours. Taking the benefits of US, we presented an integrated dual-modality imaging system in this paper that achieves three-dimensional (3D) bioluminescence tomography (BLT) with multi-view bioluminescence images and 3D US imaging. The purpose of this system is to perform non-invasive, long-term monitoring of tumor growth in 3D images. US images can enhance the accuracy of the 3D BLT reconstruction and the bioluminescence dose within an object. Furthermore, an integrated co-registered scanning geometry was used to capture the fused BLT and US images. We validated the system with an in vivo experiment involving tumor-bearing mice. The results demonstrated the feasibility of reconstructing 3D BLT images in the tumor region using 3D US images. We used the dice coefficient and locational error to evaluate the similarity between the reconstructed source region and the actual source region. The dice coefficient was 88.5%, and the locational error was 0.4 mm when comparing the BLT and 3D US images. The hybrid BLT/US system could provide significant benefits for reconstructing the source of tumor location and conducting quantitative analysis of tumor size.

Combined thermal ablation and liposomal granulocyte-macrophage colony stimulation factor increases immune cell trafficking in a small animal tumor model.

To characterize intratumoral immune cell trafficking in ablated and synchronous tumors following combined radiofrequency ablation (RFA) and systemic liposomal granulocyte-macrophage colony stimulation factor (lip-GM-CSF). Phase I, 72 rats with single subcutaneous R3230 adenocarcinoma were randomized to 6 groups: a) sham; b&c) free or liposomal GM-CSF alone; d) RFA alone; or e&f) combined with blank liposomes or lip-GM-CSF. Animals were sacrificed 3 and 7 days post-RFA. Outcomes included immunohistochemistry of dendritic cells (DCs), M1 and M2 macrophages, T-helper cells (Th1) (CD4+), cytotoxic T- lymphocytes (CTL) (CD8+), T-regulator cells (T-reg) (FoxP3+) and Fas Ligand activated CTLs (Fas-L+) in the periablational rim and untreated index tumor. M1/M2, CD4+/CD8+ and CD8+/FoxP3+ ratios were calculated. Phase II, 40 rats with double tumors were randomized to 4 groups: a) sham, b) RFA, c) RFA-BL and d) RFA-lip-GM-CSF. Synchronous untreated tumors collected at 7d were analyzed similarly. RFA-lip-GMCSF increased periablational M1, CTL and CD8+/FoxP3+ ratio at 3 and 7d, and activated CTLs 7d post-RFA (p<0.05). RFA-lip-GMSCF also increased M2, T-reg, and reduced CD4+/CD8+ 3 and 7d post-RFA respectively (p<0.05). In untreated index tumor, RFA-lip-GMCSF improved DCs, M1, CTLs and activated CTL 7d post-RFA (p<0.05). Furthermore, RFA-lip-GMSCF increased M2 at 3 and 7d, and T-reg 7d post-RFA (p<0.05). In synchronous tumors, RFA-BL and RFA-lip-GM-CSF improved DC, Th1 and CTL infiltration 7d post-RFA. Systemic liposomal GM-CSF combined with RFA improves intratumoral immune cell trafficking, specifically populations initiating (DC, M1) and executing (CTL, FasL+) anti-tumor immunity. Moreover, liposomes influence synchronous untreated metastases increasing Th1, CTL and DCs infiltration.

A deep-learning assisted bioluminescence tomography method to enable radiation targeting in rat glioblastoma

Objective. A novel solution is required for accurate 3D bioluminescence tomography (BLT) based glioblastoma (GBM) targeting. The provided solution should be computationally efficient to support real-time treatment planning, thus reducing the x-ray imaging dose imposed by high-resolution micro cone-beam CT. Approach. A novel deep-learning approach is developed to enable BLT-based tumor targeting and treatment planning for orthotopic rat GBM models. The proposed framework is trained and validated on a set of realistic Monte Carlo simulations. Finally, the trained deep learning model is tested on a limited set of BLI measurements of real rat GBM models. Significance. Bioluminescence imaging (BLI) is a 2D non-invasive optical imaging modality geared toward preclinical cancer research. It can be used to monitor tumor growth in small animal tumor models effectively and without radiation burden. However, the current state-of-the-art does not allow accurate radiation treatment planning using BLI, hence limiting BLI’s value in preclinical radiobiology research. Results. The proposed solution can achieve sub-millimeter targeting accuracy on the simulated dataset, with a median dice similarity coefficient (DSC) of 61%. The provided BLT-based planning volume achieves a median encapsulation of more than 97% of the tumor while keeping the median geometrical brain coverage below 4.2%. For the real BLI measurements, the proposed solution provided median geometrical tumor coverage of 95% and a median DSC of 42%. Dose planning using a dedicated small animal treatment planning system indicated good BLT-based treatment planning accuracy compared to ground-truth CT-based planning, where dose-volume metrics for the tumor fall within the limit of agreement for more than 95% of cases. Conclusion. The combination of flexibility, accuracy, and speed of the deep learning solutions make them a viable option for the BLT reconstruction problem and can provide BLT-based tumor targeting for the rat GBM models.

Sparse reconstruction based on dictionary learning and group structure strategy for cone-beam X-ray luminescence computed tomography.

As a dual-modal imaging technology that has emerged in recent years, cone-beam X-ray luminescence computed tomography (CB-XLCT) has exhibited promise as a tool for the early three-dimensional detection of tumors in small animals. However, due to the challenges imposed by the low absorption and high scattering of light in tissues, the CB-XLCT reconstruction problem is a severely ill-conditioned inverse problem, rendering it difficult to obtain satisfactory reconstruction results. In this study, a strategy that utilizes dictionary learning and group structure (DLGS) is proposed to achieve satisfactory CB-XLCT reconstruction performance. The group structure is employed to account for the clustering of nanophosphors in specific regions within the organism, which can enhance the interrelation of elements in the same group. Furthermore, the dictionary learning strategy is implemented to effectively capture sparse features. The performance of the proposed method was evaluated through numerical simulations and in vivo experiments. The experimental results demonstrate that the proposed method achieves superior reconstruction performance in terms of location accuracy, target shape, robustness, dual-source resolution, and in vivo practicability.

The Importance of Ultrasonography in the Evaluation of Mammary Tumors in Bitches.

The high incidence of mammary tumors in small animals is concerning. Patient history, clinical examination, physical evaluation, and imaging studies are important for clinical staging. Ultrasonography is commonly applied to investigate the presence of abdominal metastasis. However, it has been shown to provide important information regarding mammary tumors' architecture and advanced sonographic techniques can provide information regarding neovascularization, stiffness, and perfusion. Different techniques have been investigated to determine accuracy to predict the lesions' histological classification. This paper reviews the information regarding each sonographic technique in the evaluation of mammary tumors, describing the most common findings and their potential to accurately assess and predict malignancy. Even though the gold standard for the diagnosis of mammary lesions is the histopathological examination, some ultrasonographic features described can predict the potential of a lesion being malignant. Among the different sonographic techniques, elastography can be considered the most reliable modality to accurately differentiate benign from malignant tumors when malignant lesions present increased stiffness. However, the combination of all sonographic techniques can provide important information that can lead to a better therapeutic approach and clinical staging. Furthermore, the potential of the sonographic study, especially CEUS to monitor therapeutic progression, demonstrate the need of further studies.

Realization of NIR-II 3D whole-body contour and tumor blood vessels imaging in small animals using rotational stereo vision technique.

Optical imaging in the second near-infrared (NIR-II, 1000 to 1700nm) region is capable of deep tumor vascular imaging due to low light scattering and low autofluorescence. Non-invasive real-time NIR-II fluorescence imaging is instrumental in monitoring tumor status. Our aim is to develop an NIR-II fluorescence rotational stereo imaging system for 360-deg three-dimensional (3D) imaging of whole-body blood vessels, tumor vessels, and 3D contour of mice. Our study combined an NIR-II camera with a 360-deg rotational stereovision technique for tumor vascular imaging and 3D surface contour for mice. Moreover, self-made NIR-II fluorescent polymer dots were applied in high-contrast NIR-II vascular imaging, along with a 3D blood vessel enhancement algorithm for acquiring high-resolution 3D blood vessel images. The system was validated with a custom-made 3D printing phantom and in vivo experiments of 4T1 tumor-bearing mice. The results showed that the NIR-II 3D 360-deg tumor blood vessels and mice contour could be reconstructed with 0.15mm spatial resolution, 0.3mm depth resolution, and 5mm imaging depth in an ex vivo experiment. The pioneering development of an NIR-II 3D 360-deg rotational stereo imaging system was first applied in small animal tumor blood vessel imaging and 3D surface contour imaging, demonstrating its capability of reconstructing tumor blood vessels and mice contour. Therefore, the 3D imaging system can be instrumental in monitoring tumor therapy effects.

Assessing the effects of ultrasound parameters on P-selectin expression for active targeting of nanotherapeutics

P-selectin is a nanotherapeutic target for enhanced passage of nanoscale drug delivery systems across the vascular barrier and into tumors via transcytosis. While many tumors express P-selection, radiation can be used to induce expression in tumors devoid of P-selectin. This study aims to test whether ultrasound can elicit a similar response through mechanical or thermal bioeffects. Preliminary experiments were performed in vitro using brain tissue derived mouse endothelial cells. A Vevo SoniGene system was used to sonicate cells with low-intensity (2 W/cm2) pulsed ultrasound in a 12-well cell culture plate. Upregulation of P-selectin was seen using a 60 second treatment duration at 50% and 100% duty cycles via flow cytometry analysis. The mean fluorescence intensity, normalized to nontreated cells, was 32 + /- 17.4 and 103 + /- 37.2 for 50% and 100% duty cycles, respectively. Viability remained high with 72.6 + /- 14.5 and 77.5 + /- 8.3% of cells viable for both 50% and 100% duty cycle groups, respectively. These results highlight the potential of ultrasound for active targeting using non-ionizing energy and for tumors where radiation is not feasible. Future studies will identify associated bioeffects and compare ultrasound with radiation for nanotherapeutic delivery in small animal tumor models.

Treatment efficacy of low-dose 5-fluorouracil with ultrasound in mediating 5-fluorouracil-loaded microbubble cavitation in head and neck cancer

Over the past 50 years, 5-fluorouracil (5-FU) has played a critical role in the systemic chemotherapy of cancer patients. Bolus intravenous (IV) 5-FU infusion has been used due to the limitation of its extremely short half-life (10–15 min). This study used ultrasound (US) mediating 5-FU-loaded microbubbles (MBs) cavitation as a tool to increase local intratumoral 5-FU levels with a reduced dose of 5-FU (a single IV injection of 2.5 mg/kg instead of a single intraperitoneal injection of 25–200 mg/kg as used in previous studies in mice). The 5-FU-MBs were prepared with a 132 mg/mL albumin solution and a 0.30 mg/mL 5-FU solution. The diameters of the MBs and 5-FU-MBs were 1.24 ± 0.85 and 2.00 ± 0.53 µm (mean ± SEM), respectively, and the maximum loading efficiency of 5-FU on MBs was 19.04 ± 0.25%. In the in vitro study, the cell viabilities of 5-FU and 5-FU-MBs did not differ significantly, but compared with the 5-FU-MBs treatment-alone group, cell toxicity increased to 31% in the 5-FU-MBs + US group (p < 0.001). The biodistribution results indicated that the 5-FU levels of the tumors in small animals were significant higher for the 5-FU-MBs + US treatment than for either the 5-FU-MBs or 5-FU treatment with low 5-FU systemic treatment doses (2.5 mg/kg 5-FU IV). In small-animal treatment, 2.5 mg/kg 5-FU therapeutic IV doses injected into mice caused a more-significant reduction in tumor growth in the 5-FU-MBs + US group (65.9%) than in the control group after 34 days of treatment.

Depth dose measurements in water for 11C and 10C beams with therapy relevant energies

Owing to the favorable depth-dose distribution and the radiobiological properties of heavy ion radiation, ion beam therapy shows an improved success/toxicity ratio compared to conventional radiotherapy. The sharp dose gradients and very high doses in the Bragg peak region, which represent the larger physical advantage of ion beam therapy, make it also extremely sensitive to range uncertainties. The use of β+-radioactive ion beams would be ideal for simultaneous treatment and accurate online range monitoring through PET imaging. Since all the unfragmented primary ions are potentially contributing to the PET signal, these beams offer an improved image quality while preserving the physical and radiobiological advantages of the stable counterparts. The challenging production of radioactive ion beams and the difficulties in reaching high intensities, have discouraged their clinical application. In this context, the project Biomedical Applications of Radioactive ion Beams (BARB) started at GSI (Helmholtzzentrum für Schwerionenforschung GmbH) with the main goal to assess the technical feasibility and investigate possible advantages of radioactive ion beams on the pre-clinical level. During the first experimental campaign 11C and 10C beams were produced and isotopically separated with the FRagment Separator (FRS) at GSI. The β+-radioactive ion beams were produced with a beam purity of 99% for all the beam investigated (except one case where it was 94%) and intensities potentially sufficient to treat a small animal tumors within few minutes of irradiation time, ∼106 particle per spill for the 10C and ∼107 particle per spill for the 11C beam, respectively. The impact of different ion optical parameters on the depth dose distribution was studied with a precision water column system. In this work, the measured depth dose distributions are presented together with results from Monte Carlo simulations using the FLUKA software.

Open-source mobile multispectral imaging system and its applications in biological sample sensing

Visible-near-infrared spectroscopy data can be utilized as an important quantitative indicator of biomolecular quantitative analysis. When acquiring spectral information, hyperspectral/multispectral imaging systems can obtain the spatial information of the object of interest. This allows the complete spatial–spectral information of the object of interest to be acquired and the spatial distribution of biomolecules to be analyzed. In this study, we present an open-source mobile multispectral imaging system, test the influence of the utilization of LEDs on the multispectral image, and design image-processing algorithms to correct this influence. Todemonstrate the effectivenessofthesystem, the system is applied to meat freshness analysis, small-animal tumor in-vivo imaging, and chlorophyll spatial distribution imaging. The experimental results verify that our system has stable performance and is compatible with a wide range of spectral imaging applications.

Abstract No. 351 Microneedle array platform with spatial control of heating and drug delivery profiles for experimental studies in small animals

Therapeutic strategies combining energy-based interventions and intratumoral immunotherapy are under investigation, however, the relationship between spatial energy-delivery profiles and bioeffects are not currently well understood. We are developing a microneedle array-based platform for experimental studies in small-animal tumor models investigating intratumoral immunotherapy in conjunction energy-based therapies. This abstract reports on the simulation-based characterization of spatially modulated thermal profiles achievable with the microneedle array.

System for delivering microwave ablation to subcutaneous tumors in small-animals under high-field MRI thermometry guidance

Purpose Bio-effects following thermal treatments are a function of the achieved temperature profile in tissue, which can be estimated across tumor volumes with real-time MRI thermometry (MRIT). Here, we report on expansion of a previously developed small-animal microwave hyperthermia system integrated with MRIT for delivering thermal ablation to subcutaneously implanted tumors in mice. Methods Computational models were employed to assess suitability of the 2.45 GHz microwave applicators for delivering ablation to subcutaneous tumor targets in mice. Phantoms and ex-vivo tissues were heated to temperatures in the range 47–67 °C with custom-made microwave applicators for validating MRIT with the proton resonance frequency shift method against fiberoptic thermometry. HAC15 tumors implanted in nude mice (n = 6) were ablated in vivo and monitored with MRIT in multiple planes. One day post ablation, animals were euthanized, and excised tumors were processed for viability assessment. Results Average absolute error between temperatures from fiberoptic sensors and MRIT was 0.6 °C across all ex-vivo ablations. During in-vivo experiments, tumors with volumes ranging between 5.4–35.9 mm3 (mean 14.2 mm3) were ablated (duration: 103–150 s) to achieve 55 °C at the tumor boundary. Thermal doses ≥240 CEM43 were achieved across 90.7–98.0% of tumor volumes for four cases. Ablations were incomplete for remaining cases, attributed to motion-affected thermometry. Thermal dose-based ablative tumor coverage agreed with viability assessment of excised tumors. Conclusions We have developed a system for delivering microwave ablation to subcutaneous tumors in small animals under MRIT guidance and demonstrated its performance in-vivo.

Experimental evaluation of targeting accuracy of ultrasound imaging-guided robotic HIFU ablative system for the treatment of solid tumors in pre-clinical studies

We have designed and built low-cost compact ultrasound imaging-guided robotic HIFU (High-Intensity Focused Ultrasound) ablation device for thermal damage of solid tumors in small animals. Before this device is used to treat animals, experimental studies on ex vivo tissues were necessary to assess the accuracy of its targeting, ensuring the safety of therapy. The objective of this study was to assess the targeting accuracy of our device in the focal and axial plane of the HIFU beam using ex vivo tissue embedded in a reference cylindrical chamber inside which a coaxial cylindrical volume with a smaller diameter was ablated. HIFU beams with selected acoustic parameters, generated by a singe-element bowl-shaped 64-mm HIFU transducer operating at 1.08 MHz or 3.21 MHz frequency, were propagated in two-layer media: water-tissue (50 mm-40 mm) and focused at 12.6-mm depth below the tissue surface. Cylindrical necrotic lesions of various size were created by moving the chamber using a computer-controlled precise positioning unit. Lesions formed were compared with those intended for treatment using various visualization methods and displacement between their centers were determined. The targeting accuracy in the focal and axial planes was found to be respectively about 98% and 86% when determined from photos and about 88% and 76% when determined from MR images. The displacement between the centers of the necrotic lesion formed and planned for treatment was about 1 mm in the focal plane and about 2 mm in the axial plane. Our ablation device can be used as an effective and safe tool to plan, monitor and treat solid tumors in small animals and to test new anti-cancer drugs in preclinical studies.

A General Strategy to Design Highly Fluorogenic Far-Red and Near-Infrared Tetrazine Bioorthogonal Probes.

Highly fluorogenic tetrazine bioorthogonal probes emitting at near-infrared wavelengths are in strong demand for biomedical imaging applications. Herein, we have developed a strategy for forming a palette of novel Huaxi-Fluor probes in situ, whose fluorescence increases hundreds of times upon forming the bioorthogonal reaction product, pyridazine. The resulting probes show large Stokes shifts and high quantum yields. Manipulating the conjugate length and pull-push strength in the fluorophore skeleton allows the emission wavelength to be fine-tuned from 556 to 728 nm. The highly photo-stable and biocompatible probes are suitable for visualizing organelles in live cells without a washing step and for imaging of tumors in live small animals to depths of 500 μm by two-photon excitation.

A General Strategy to Design Highly Fluorogenic Far‐Red and Near‐Infrared Tetrazine Bioorthogonal Probes

AbstractHighly fluorogenic tetrazine bioorthogonal probes emitting at near‐infrared wavelengths are in strong demand for biomedical imaging applications. Herein, we have developed a strategy for forming a palette of novel Huaxi‐Fluor probes in situ, whose fluorescence increases hundreds of times upon forming the bioorthogonal reaction product, pyridazine. The resulting probes show large Stokes shifts and high quantum yields. Manipulating the conjugate length and pull–push strength in the fluorophore skeleton allows the emission wavelength to be fine‐tuned from 556 to 728 nm. The highly photo‐stable and biocompatible probes are suitable for visualizing organelles in live cells without a washing step and for imaging of tumors in live small animals to depths of 500 μm by two‐photon excitation.

Teleterapia aplicada em tumores de cabeça e pescoço em pequenos animais

O câncer é uma neoplasia que acomete seres humanos e animais, sendo responsável pelo maior número de mortalidade. A radioterapia é uma prática médica, que utiliza radiação ionizante para eliminar ou impedir a multiplicação das células cancerígenas. A radioterapia divide-se em duas modalidades, denominadas de braquiterapia e teleterapia. Essa última vem adquirindo espaço dentro da medicina veterinária, principalmente para tratamento de tumores de cabeça e pescoço. Contudo esse trabalho propôs copilar e descrever os principais casos de teleterapia aplicada em tumores de cabeça e pescoço em pequenos animais por meio da literatura. Após uma breve revisão de literatura elaborada nesse estudo, foi possível identificar as principais aplicações da teleterapia nos tumores de cabeça e pescoço em pequenos animais e destacar eficácia dessa modalidade terapêutica na sobrevida dos animais envolvidos.

Evaluation of Brain Tumor in Small Animals Using Plane Wave-Based Power Doppler Imaging

Precisely evaluating the characteristics of a glioma tumor in vivo is challenging when performing surgical resection clinically. The infiltration characteristics of a tumor make precise resection difficult because of uncertainties about the surrounding vasculature and the relationships with functional structures. Magnetic resonance imaging is routinely used to distinguish the area of a glioma, but it cannot resolve details of the vascular network around or inside the tumor. Ultrasound imaging is a real-time imaging modality that has been applied clinically in intra-operative surgery, and the sensitivity of flow measurements in the brain is improved by ultrafast plane wave imaging. This study applies a plane wave-based power Doppler imaging method to visualize the blood flow distribution in glioma models in vivo. This new imaging method makes it possible to delineate the flow structure of a glioma tumor in the brain of a small animal. The tumor can be distinguished from normal brain tissue, and different sections of the tumor contain different flow structures. The normalized blood flow intensities (mean ± standard deviation) within regions of interest were 0.33 ± 0.13, 0.72 ± 0.15, 0.36 ± 0.23 and 0.06 ± 0.07 for the type I normal rat, type I glioma rat, type II normal rat and type II glioma rat, respectively. Quantification analysis verified the feasibility of using this plane wave-based Doppler imaging method to evaluate brain tumors in small animals.

Investigation of Optimal Physical Parameters for Precise Proton Irradiation of Orthotopic Tumors in Small Animals

The lack of evidence of biomarkers identifying patients who wouldbenefit from proton therapy has driven the emergence of preclinical proton irradiation platforms using advanced small-animal models to mimic clinical therapeutic conditions. This study aimed to determine the optimal physical parameters of the proton beam with a high radiation targeting accuracy, considering small-animal tumors can reach millimetric dimensions at a maximum depth of about 2cm. Several treatment plans, simulated using Geant4, were generated with different proton beam features to assess the optimal physical parameters for small-volume irradiations. The quality of each treatment plan was estimated by dose-volume histograms and gamma index maps. Because of its low-energy straggling, low-energy proton (<50MeV) single-field irradiation can generate homogeneous spread-out Bragg peaks to deliver a uniform dose in millimeter-sized tumors, while sparing healthy tissues located within or near the target volume. However, multifield irradiation can limit the dose delivered in critical structures surrounding the target for attenuated high-energy beams (E>160MeV). Low-energy proton beam platforms are suitable for precision irradiation for translational radiobiology studies.