Small Animal Tumor Research Articles

Combination Radiofrequency Ablation and Intravenous Radiolabeled Liposomal Doxorubicin: Imaging and Quantification of Increased Drug Delivery to Tumors

To identify, with noninvasive imaging, the zone of radiopharmaceutical uptake after combination therapy with radiofrequency (RF) ablation and intravenous administration of technetium 99m ((99m)Tc) liposomal doxorubicin in a small-animal tumor model, and to quantify and correlate the uptake by using imaging and tissue counting of intratumoral doxorubicin accumulation. This study was approved by the animal care committee. Two phases of animal experiments were performed. In the first experiment, a single human head-and-neck squamous cell carcinoma tumor was grown in each of 10 male nude rats. Seven of these animals were treated with intravenous (99m)Tc-liposomal doxorubicin followed by RF tumor ablation at a mean temperature of 70 degrees C + or - 2 for 5 minutes, and three were treated with intravenous (99m)Tc-liposomal doxorubicin only. Combination single photon emission computed tomography-computed tomography (SPECT/CT) was performed at 15 minutes, 4 hours, and 20 hours after therapy. In the second experiment, two tumors each were grown in 11 rats, but only one of the tumors was ablated after intravenous administration of (99m)Tc-liposomal doxorubicin. SPECT/CT and planar scintigraphy were performed at the same posttreatment intervals applied in the first experiment, with additional planar imaging performed at 44 hours. After imaging, tissue counting in the excised tumors was performed. Radiotracer uptake, as determined with imaging and tissue counting, was quantified and compared. In a subset of three animals, intratumoral doxorubicin accumulation was determined with fluorimetry and correlated with the imaging and tissue-counting data. At both SPECT/CT and planar scintigraphy, increased uptake of (99m)Tc-liposomal doxorubicin was visibly apparent in the ablated tumors. Results of quantitative analysis with both imaging and tissue counting confirmed significantly greater uptake in the RF ablation-treated tumors (P < .001). Intratumoral doxorubicin accumulation correlated closely with imaging (r = 0.9185-0.9871) and tissue-counting (r = 0.995) results. Study results show that increased delivery of intravenous liposomal doxorubicin to tumors combined with RF ablation can be depicted and quantified with noninvasive imaging.

Small animal tumour imaging with MRI and the ECAT EXACT scanner: application of partial volume correction and comparison with microPET data

Partial volume effects caused by limited spatial resolution of conventional positron emission tomography (PET) scanners result in an underestimation of the activity concentration in small tumours. The aim of the study was to evaluate the feasibility of small animal tumour imaging with the clinical PET scanner ECAT EXACT after partial volume correction based on MRI calculations. The same tumour model was examined additionally with the small animal PET system, microPET focus 120. Before the ECAT EXACT studies recovery coefficients for different sphere volumes were generated with phantom experiments. For the following in-vivo study DS-sarcoma cells were implanted on both hind foot dorsum of male Sprague-Dawley rats. In-vivo tumour volume calculations were done with the high-resolution MRI system, Magnetom Vision Experimental. Dynamic F-fluorodeoxyglucose (FDG) PET was performed with the scanner ECAT EXACT (5 MBq intravenous, two-dimensional mode, n = 16 tumours) or with the microPET focus 120 (20 MBq intravenous, two-dimensional mode, n = 10 tumours). The animals were then killed, the tumours rapidly explanted, weighed and homogenized. The concentration of F-FDG was measured with a gamma counter and decay corrected; the ex-vivo F-FDG concentration was compared with the mean tumour activity concentration of the PET data. Using the ECAT EXACT mean underestimation of actual tumour F-FDG concentration was 35.4%, for partial volume-corrected data this error decreased to 1.7%. In addition, after partial volume correction congruence and linear correlation between the regions of interest-based activity concentration and ex-vivo measurements were excellent (r = 0.98). These results were quite similar to the microPET experiments without partial volume correction: r = 0.99. These data indicate that partial volume correction might allow use of the clinical PET system, ECAT EXACT, for the metabolic assessment of small animal tumours >/=10 mm with sufficient accuracy if no dedicated animal PET is available.

An Optimized Telomerase-Specific Lentivirus for Optical Imaging of Tumors

Advances in medical imaging techniques, such as ultrasound, computed tomography, magnetic resonance imaging, and positron emission tomography, have made great progress in detecting tumors. However, these imaging techniques are unable to differentiate malignant tumors from benign ones. Recently developed optical imaging of tumors in small animals provides a useful method to distinguish malignant tumors from their surrounding normal tissues. Human telomerase reverse transcriptase (hTERT) is normally inactivated in most somatic cells, whereas it is commonly reactivated in many cancer cells. In this study, we constructed a lentiviral vector that expresses green fluorescent protein (GFP) driven by an optimized hTERT promoter to create a noninvasive tumor-specific imaging methodology. The activity of this optimized hTERT promoter was found to be equal to the activity of SV40 and cytomegalovirus promoters. In vitro experiments showed that GFP was only expressed in telomerase-positive tumor cells infected with this lentivirus, whereas there was no GFP expression in telomerase-negative tumor cells or normal somatic cells. We also found that subcutaneous telomerase-positive tumors could be visualized 24 hours after an intratumoral injection with this lentivirus by using a charge-coupled device (CCD) camera. In contrast, telomerase-negative tumors could not be imaged after an intratumoral injection even for 30 days. These results suggest that infection with lentivirus containing this optimized hTERT promoter might be a useful diagnostic tool for the real-time visualization of macroscopically invisible tumor tissues using a highly sensitive CCD imaging system.

Bioluminescent imaging: a critical tool in pre‐clinical oncology research

Bioluminescent imaging (BLI) is a non-invasive imaging modality widely used in the field of pre-clinical oncology research. Imaging of small animal tumour models using BLI involves the generation of light by luciferase-expressing cells in the animal following administration of substrate. This light may be imaged using an external detector. The technique allows a variety of tumour-associated properties to be visualized dynamically in living models. The increasing use of BLI as a small-animal imaging modality has led to advances in the development of xenogeneic, orthotopic, and genetically engineered animal models expressing luciferase genes. This review aims to provide insight into the principles of BLI and its applications in cancer research. Many studies to assess tumour growth and development, as well as efficacy of candidate therapeutics, have been performed using BLI. More recently, advances have also been made using bioluminescent imaging in studies of protein-protein interactions, genetic screening, cell-cycle regulators, and spontaneous cancer development. Such novel studies highlight the versatility and potential of bioluminescent imaging in future oncological research.

Using Optical Spectroscopy to Longitudinally Monitor Physiological Changes within Solid Tumors

The feasibility of using quantitative diffuse reflectance spectroscopy to longitudinally monitor physiological response to cancer therapy was evaluated in a preclinical model. This study included two groups of nude mice bearing 4T1 flank tumors (N = 50), half of which were treated with a maximum tolerated dose of doxorubicin (DOX). Diffuse reflectance spectra were collected from tumors during a period of 2 weeks using a fiber-optic probe coupled to a spectrometer. These spectra were quantified using an inverse scalable Monte Carlo model of light transport in tissue to extract the concentrations of oxygenated, deoxygenated hemoglobin (dHb), and a wavelength mean reduced scattering coefficient (<µs′>). The tumor growth rates of the treated and control groups were nearly identical, as were changes in the scattering parameter <µs′> during this time frame. However, tumors treated with DOX showed a transient but significant increase in blood oxygen saturation. A comparison between the optically derived and immunohistochemical end points in a subset of the 50 animals showed that the temporal kinetics of dHb concentration and <µs′> were highly concordant with those of hypoxic and necrotic fractions, respectively. In conclusion, optical methods could function as a “screening” technology in longitudinal studies of small animal tumor models to accelerate development and testing of new anticancer drugs. This technique could isolate specific landmark time points at which more expensive and sophisticated imaging methods or immunohistochemistry could be performed.

Measuring Brain Tumor Growth: Combined Bioluminescence Imaging–Magnetic Resonance Imaging Strategy

Small-animal tumor models are essential for developing translational therapeutic strategies in oncology research, with imaging having an increasingly important role. Magnetic resonance imaging (MRI) offers tumor localization, volumetric measurement, and the potential for advanced physiologic imaging but is less well suited to high-throughput studies and has limited capacity to assess early tumor growth. Bioluminescence imaging (BLI) identifies tumors early, monitors tumor growth, and efficiently measures response to therapeutic intervention. Generally, BLI signals have been found to correlate well with magnetic resonance measurements of tumor volume. However, in our studies of small-animal models of malignant brain tumors, we have observed specific instances in which BLI data do not correlate with corresponding MRIs. These observations led us to hypothesize that use of BLI and MRI together, rather than in isolation, would allow more effective and efficient measures of tumor growth in preclinical studies. Herein we describe combining BLI and MRI studies to characterize tumor growth in a mouse model of glioblastoma. The results led us to suggest a cost-effective, multimodality strategy for selecting cohorts of animals with similar tumor growth patterns that improves the accuracy of longitudinal in vivo measurements of tumor growth and treatment response in preclinical therapeutic studies.

Near-infrared phosphorescent polymeric nanomicelles: efficient optical probes for tumor imaging and detection.

We report a formulation of near-infrared (near-IR) phosphorescent polymeric nanomicelles and their use for in vivo high-contrast optical imaging, targeting, and detection of tumors in small animals. Near-IR phosphorescent molecules of Pt(II)-tetraphenyltetranaphthoporphyrin (Pt(TPNP)) were found to maintain their near-IR phosphorescence properties when encapsulated into phospholipid nanomicelles. The prepared phosphorescent micelles are of approximately 100 nm size and are highly stable in aqueous suspensions. A large spectral separation between the Pt(TPNP) absorption, with a peak at approximately 700 nm, and its phosphorescence emission, with a peak at approximately 900 nm, allows a dramatic decrease in the level of background autofluorescence and scattered excitation light in the near-IR spectral range, where the signal from the phosphorescent probe is observed. In vivo animal imaging with subcutaneously xenografted tumor-bearing mice has resulted in high contrast optical images, indicating highly specific accumulation of the phosphorescent micelles into tumors. Using optical imaging with near-IR phosphorescent nanomicelles, detection of smaller, visually undetectable tumors has also been demonstrated.

SU-FF-J-160: Spatially Fractionated Radiation Therapy (GRID) On Implanted Tumors Using a Small Animal Conformal Radiation Therapy System

Purpose: To deliver spatially fractionated (GRID) radiation fields to murine tumors using a high precision small animal conformal radiation therapy device (SACRTD). Method and Materials: The SACRTD is a “gantry” based image‐guide system with a special collimating assembly that allows field sizes down to 0.5 mm in diameter at isocenter. The precise positioning of the target/beam is achieved by a six‐degree of freedom robotic system (Adept Technology, Pleasanton, CA) which has positional repeatability of ±0.020mm in XYZ directions. The system can be used to deliver small GRID fields with varying open‐to‐close area ratios. Immunohistochemistry for DNA damage after 10 Gy to a 1cm depth GRID therapy was performed in B16 murine melanoma tumors. The GRID pattern consisted of an array of 7 beams of 1 mm in diameter at isocenter with center‐to‐center separation of 2 mm. Tumorgrowth rates and cell survival were assessed. Results : The exit dose recorded by Gafchromic film confirmed that the GRID radiation pattern was delivered with high precision. Histology showed the radiation induced DNA strand breaks in the open regions of the GRID field. Approximately 55% of clonogenic cells in the B16 tumors were killed by the single GRID dose. Interestingly, mice receiving GRID alone did not have significant tumorgrowth delay compared to untreated tumors. However, in the group that received GRID therapy followed by Anginex anti‐angiogenic peptide for 5 days there was a noticeable delay in tumorgrowth compared to tumors receiving 10 Gy GRID alone. Conclusion: This preliminary biological study shows the usefulness and flexibility of the SACRTD to deliver precise radiation patterns to implanted tumors in small animals. The system facilitates in vivo radiobiological studies and promotes translational research in radiationoncology.

TU‐C‐BRD‐07: Translational Research with Small Animal IGRT

Radiation therapy is a critical component in the management of cancer. However, our understanding of radiotherapy must continue to grow with improvements in conformality (e.g., IMRT) and as more targeted agents become available. Maximizing the therapeutic ratio will require a thorough understanding of biology of tumors and normal tissues. Small animal models of tumor response and normal tissue toxicity can provide unique insights into these issues, but have inherent limitations and challenges which must be overcome. As small animal image‐guided radiation therapy (IGRT) becomes feasible, one of the most important issues becomes “What questions do we want to ask?”. Pure radiotherapy questions such as dose, volume, and time/fractionation can be explored in appropriate small animal tumor models while monitoring normal tissue effects. When combined with the ever‐increasing number of targeted agents, small animal IGRT becomes a powerful pre‐clinical tool that may allow optimal selection of agents and improve the timing and sequencing of concurrent therapies. After strong models of tumor control and normal tissue response are established, exploration of response biomarkers including novel imaging modalities becomes feasible. The wide‐spread availability of small animal multi‐modality imaging including CT, MR, optical, and US combined with novel contrast agents makes this an especially rich area of exploration. Some examples of previous small animal radiotherapy experiments with a brain tumor model and ongoing exploration of normal tissues effects in lung will be reviewed and potential future studies attempting to link pre‐clinical and clinical data will be outlined.Learning Objectives:At the end of this lecture, the audience will be able to:1. Describe some of the challenges of small animal models.2. Discuss the range of biologic experiments which may be feasible.

Tumor models and specific contrast agents for small animal imaging in oncology

Despite the widespread use of various imaging modalities in clinical and experimental oncology without or with combined application of commercially available nonspecific contrast agents (CAs), development of tissue- or organ- or disease-specific CAs has been a continuing effort for pursuing ever-improved sensitivity, specificity, and applicability. This is particularly true with magnetic resonance imaging (MRI) due to its intrinsic superb spatial/temporal/contrast resolutions and adequate detectability for tiny amount of substances. In this context, research using small animal tumor models has played an indispensible role in preclinical exploration of tissue specific CAs. Emphasizing more on methodological and practical aspects, this article aims to share our cumulated experiences on how to create tumor models for evaluation and development of new tissue specific MRI CAs and how to apply such models in imaging-based research studies. With the results that are repeatedly confirmed by later clinical applications in cancer patients, some of our early preclinical studies have contributed to the designs of subsequent clinical trials on the new CAs, some studies have predicted new utilities of these CAs; and other studies have led to the discoveries of new tissue- or disease-specific CAs with novel diagnostic or even therapeutic potentials. Among commonly adopted tumor models, the chemically induced and surgically implanted nodules in the liver prove very useful to simulate primary and metastatic intrahepatic tumors, respectively in clinical patients. The methods to create tumor models have eased procedures and yielded high success rates. The specific properties of the new CAs could be outshined by intraindividual comparison to the commercial CAs as nonspecific controls. Meticulous imaging-microangiography-histology matching techniques guaranteed colocalization of the lesion on in vivo MRI and postmortem tissue specimen, hence correct imaging interpretation and longstanding conclusions. As exemplified in the real study cases, the present experimental set-up proves applicable in small animals for imaging-based oncological investigations, and may provide a platform for the currently booming molecular imaging in a multimodality environment.

Quantitative Estimation of Dynamic Contrast Enhanced MRI Parameters in Rat Brain Gliomas Using a Dual Surface Coil System

The study of vascular targeted cancer therapies is critically dependent on the development of noninvasive methods for assessing changes in vascular permeability and blood flow in small-animal tumor models. A multicoil apparatus consisting of two receive-only surface coils for observation of the rat brain and chest, a whole-body transmit-only volume coil, and the switching circuitry necessary for sharing a single receiver channel between the two surface coils was constructed for the parallel observation of left ventricular arterial input function and magnetic resonance imaging (MRI) signal intensity kinetics in the rat brain. Dynamic contrast-enhanced MRI was performed on four Fischer rats bearing intracranial 9L gliomas, and the dynamic data were evaluated using the bolus-enhanced relaxation overview (BOLERO) model yielding maps of K(trans), v(e), and tau(i) values from the tumor. The use of the multicoil apparatus resulted in images with high signal-to-noise ratios from the rat brain and chest in parallel, with no detectable crosstalk between the surface coils. The BOLERO method accurately fit the observed data to within experimental error. Mean values of the parameters generated by the BOLERO analysis for the tumor were K(trans) = 0.023 +/- 0.014 s(-1), tau(i) = 1.3 +/- 0.6 seconds, and v(e) = 0.51. K(trans) and tau(i) values were slightly elevated in the tumor periphery, whereas v(e) was elevated in the tumor core. These results demonstrate the feasibility of measuring quantitative dynamic contrast-enhanced MRI parameters in a rat brain tumor model using a multicoil apparatus. These methods might play an important role in determining the efficacy of antiangiogenic therapies in small-animal models.

Endoscopic‐Assisted Intracranial Tumor Removal in Dogs and Cats: Long‐Term Outcome of 39 Cases

The benefits of endoscopic assistance to remove intracranial tumors in small animals are not described. To evaluate the effectiveness of endoscopic-assisted intracranial tumor removal in dogs and cats. Thirty-three dogs and 6 cats with intracranial tumors. Retrospective study. CBC, serum chemistry profile, coagulation testing, blood typing, and systemic tumor staging, which included 3-view thoracic radiographs and abdominal ultrasound examination, were performed to detect other significant underlying disease in preparation of the animal for surgery. Magnetic resonance imaging was used in 37/39 cases to image the brain tumor. Surgical approach was dictated by the location of the tumor. Histopathologic examination of the tumor tissue was performed in all cases. Animals were followed throughout their postoperative course for complications and survival times. Statistical analysis (Kaplan-Meier curves) was performed to obtain median survival times in dogs with meningiomas. Use of an endoscope resulted in visualization of residual tumor and potentially more complete removal of the brain tumors. There were no clinically important complications associated with the use of the endoscope. Median survival time was 2,104 days for dogs with forebrain meningiomas surgically removed with endoscopic assistance and 702 days for dogs with caudal brain meningiomas. These results demonstrate that the use of an endoscope to assist in brain tumor removal is apparently safe and might result in improved survival times.

Practical method for radioactivity distribution analysis in small-animal PET cancer studies

We present a practical method for radioactivity distribution analysis in small-animal tumors and organs using positron emission tomography imaging with a calibrated source of known activity and size in the field of view. We reconstruct the imaged mouse together with a source under the same conditions, using an iterative method, Maximum likelihood expectation-maximization with system modeling, capable of delivering high-resolution images. Corrections for the ratios of geometrical efficiencies, radioisotope decay in time and photon attenuation are included in the algorithm. We demonstrate reconstruction results for the amount of radioactivity within the scanned mouse in a sample study of osteolytic and osteoblastic bone metastasis from prostate cancer xenografts. Data acquisition was performed on the small-animal PET system, which was tested with different radioactive sources, phantoms and animals to achieve high sensitivity and spatial resolution. Our method uses high-resolution images to determine the volume of organ or tumor and the amount of their radioactivity has the possibility of saving time, effort and the necessity to sacrifice animals. This method has utility for prognosis and quantitative analysis in small-animal cancer studies, and will enhance the assessment of characteristics of tumor growth, identifying metastases, and potentially determining the effectiveness of cancer treatment. The possible application for this technique could be useful for the organ radioactivity dosimetry studies.

Development of a quantitative analysis method for measuring the change in vascular structure of malignant tumors in small experimental animals

The aim of this study was to develop a detailed and quantitative X-ray imaging evaluation method for analyzing the vascular structure of malignant tumors in small experimental animals. A microfocus tube X-ray imaging system and a computed radiography system were used to capture images directly at 7× magnification. Various parameters of the vascular structures in the digital images were quantitatively analyzed with image analysis software after the vascular structure patterns were extracted by a mathematical morphology filter. The evaluation included the following three stages: assessment of the digital images drawn with graphics software, evaluation of digital X-ray images of vascular structure model phantoms made from copper wire, and assessment of the angiography of the mouse tumor model. In the quantitative analysis of the digital images, each vascular structure parameter increased as the thickness, length, and area of the test chart increased. In contrast, nonvascular structure parameters decreased with increases in the thickness, length, and area of the test chart. The results of the analysis of the digital X-ray images of model phantoms were similar to those of the digital test chart image. Vascular structure parameter values were higher in the tumor model mouse than in the control mouse. In contrast, values of parameters that measured the nonblood vessel parameters were lower in the tumor model mouse than in the control mouse. The results of our preliminary investigation suggest that our quantitative X-ray imaging evaluation method may be useful for analyzing the vascular structure of tumors in small experimental animals.

SU-GG-J-44: Carbon Nanotube Field Emission Technology Enables Novel Imaging and Irradiation System Development for Cancer Research and Clinical Application

Purpose:Carbon nanotubefield emission is an emerging nanotechnology for novel x‐ray imaging and radiation delivery systems development for cancer research and clinical application. In this presentation we will give a general review of the nanotechnology and its applications in the development of novel devices including CT imaging,tomosynthesis, and cancer research radiation delivery systems. Method and Materials:Carbon nanotubefield emission is a based on the unique properties of a nanomaterial called carbon nanotubes(CNT).CNT is the newest carbon allotrope discovered in 1991 and it is comprised of either a single graphene shell, called the single‐wall carbon nanotube, or multiple concentric graphene shells termed a multi‐wall carbon nanotube. The signature feature is a very large aspect ratio (ratio of diameter to length) that is typically is on the order 103. The high aspect ratio makes CNTs a practical and excellent field emitter that can produce high current density with intrinsically small divergence and extremely high temporal resolution. More importantly, its unprecedented flexibility in cathode design has launched new creativity in imaging and therapy system development. Results: We will show examples of our research development on CNTfield emission based imaging and irradiation systems that include 4D micro‐RT, stationary tomosynthesis, multi‐pixel electron microbeam cellular irradiator under real time microscope observation, and multi‐pixel x‐ray micro‐CT‐RT image‐guided and intensity‐modulated radiation for small animal tumor models. The technical challenges of the CNTfield emissiontechnology will also be discussed. Conclusion:Carbon nanotubefield emissiontechnology has shown great promise in developing novel imaging and radiation systems that can potentially advance cancer research and improve the quality and efficiency of cancer diagnosis and treatment.

SU-GG-I-155: A QA Program for US Preclinical Tumor Drug Response Testing

Purpose: Growing concern with rising costs of preclinical testing of anti‐tumor drugs in animalmodels creates demand for improvements in measurement accuracy. Caliper tumor volume measurements are the most commonly accepted parameter in tumor response studies. High frequency ultrasound (∼35 MHz) is more accurate and the least expensive imaging measurement device for rodent tumors. The accuracy of US measurements is unfortunately highly dependent on operator performance and training. Although commercial phantoms for quality assurance (QA) in clinical ultrasound are common no source of QA phantoms was available to validate the accuracy of tumor response to chemotherapeutic agents in rodent models.Method and Materials: For these studies a special purpose ultrasound(US) phantom was designed using Gammex ultrasound materials and manufacturing expertise from clinical radiology. The prototype phantom is composed of four parts; A) high contrast uniformly spaced wire tool to measure vertical (depth) accuracy, horizontal accuracy and linearity, B) low contrast variable diameter cylinder accuracy tool at uniform depth, C) low contrast cylinder 2mm‐diameter accuracy at variable depth tool and D) low contrast hyperechoic spheres to measure tumor volume accuracy. USimages of the phantom were acquired and tumor volume measurements made with a 35MHz ultrasound Vevo 707 Visualsonics Rodent Imager.Results: The measurements showed that the errors are generally less than ±5%. Large inter‐operator errors approaching 50%, however, were observed due to 1. insufficient training, 2. undeveloped measurement protocols and 3. simple operator errors. Conclusion: The materials and manufacturing procedures for Gammex US phantoms for human studies can be used with smaller imaging objects suitable for mouse models. Preliminary experience shows potential for improved inter‐institutional variability by improving measurement protocols and operator training. These phantoms are expected to improve small animaltumor response measurements, and reduce the cost of cancer drug testing by improving confidence levels of outcomes.

Malignant spinal meningioma in a CD-1 mouse

Spontaneous meningiomas are extremely rare tumors in small laboratory animals, except in some strains of rats and in the B6C3F1 mouse. We report the case of a male CD-1 mouse in poor health condition, with severe apathy and partial paresis of hindlegs. No macroscopic lesion was noticed at necropsy. Microscopic examination revealed the presence of a malignant meningioma (approximately 3 mm in diameter) at the distal lumbar level of the spinal cord, invading the vertebral canal, and bilaterally the ventral and dorsal nerve roots and the dorsal root ganglia. The tumor displayed highly cellular sheets of polygonal cells with a well-delineated, abundant, eosinophilic cytoplasm and scarce fibrovascular stroma; epithelioid and sarcomatous areas were also present. The mitotic activity was moderate. Tumor cells expressed vimentin immunoreactivity and were negative for periodic acid-Schiff (PAS), silver impregnation for reticulin, chromogranin A, glial fibrillary acidic protein (GFAP), cytokeratin (CK) and S-100 protein. The diagnosis of malignant spinal meningioma was based on the morphologic features of the neoplasm, the evidence of local invasion and the immunohistochemical results.

Fluorescence diffuse tomography for detection of red fluorescent protein expressed tumors in small animals

A fluorescence diffuse tomography (FDT) setup for monitoring tumor growth in small animals has been created. In this setup an animal is scanned in the transilluminative configuration by a single source and detector pair. To remove stray light in the detection system, we used a combination of interferometric and absorption filters. To reduce the scanning time, an experimental animal was scanned using the following algorithm: (1) large-step scanning to obtain a general view of the animal (source and detector move synchronously); (2) selection of the fluorescing region; and (3) small-step scanning of the selected region and different relative shifts between the source and detector to obtain sufficient information for 3D reconstruction. We created a reconstruction algorithm based on the Holder norm to estimate the fluorophore distribution. This algorithm converges to the solution with a minimum number of fluorescing zones. The use of tumor cell lines transfected with fluorescent proteins allowed us to conduct intravital monitoring studies. Cell lines of human melanomas Mel-P, Mel-Ibr, Mel-Kor, and human embryonic kidney HEK293 Phoenix were transfected with DsRed-Express and Turbo-RFP genes. The emission of red fluorescent proteins (RFPs) in the long-wave optical range permits detection of deep-seated tumors. In vivo experiments were conducted immediately after subcutaneous injection of fluorescing cells into small animals.

SU‐FF‐T‐20: A Method to Achieve Uniform Dose Distributions in Small Animal Subcutaneous Tumors

Purpose: In the current radiotherapy paradigm, a major treatment planning goal is target dose uniformity. However, a boost dose to as large a fraction as possible of the target volume (partial target boosting) may improve local control without increasing the risk of normal tissue injury. We are investigating the feasibility of using 6 MV photon beam from Varian 2100 Linac to deliver controlled, non‐uniform dose distributions to subcutaneous small animal tumors. The focus here is to achieve dose uniformity as the first step. Methods: A superficial structure was created near the thigh of a healthy mouse to simulate a subcutaneous tumor. It had a maximum dimension of 9mm and density equal to water. The fast Monte Carlo code, Dose Planning Method, (DPM) was coupled to our research treatment planning system, CERR (Computational Environment for Radiotherapy Research), to conduct the planning study. The mouse was placed on the in‐house microRT system. Different boluses and beam arrangements were tested. Results: By computing and evaluating the different plans using 2, 4, and 7mm boluses, it was found that 4mm bolus was enough to provide buildup. Two slightly‐angled (35° and 240°) or parallel‐opposed (60° and 240°) beams can achieve a tumor dose with 3% RMS, the minimum and maximum dose as 0.89Gy and 1.05Gy respectively, for the mean dose 1Gy. This suggested that the uniform dose distributions can be delivered. Conclusions: 6MV photon beam is capable of delivering uniform dose on a superficial tumor of 9mm. Thus it is achievable to deliver a non‐uniform dose on the tumor, provided accurate positioning and beam collimation, to facilitate the investigation of tumor response to heterogeneous dose. The microRT hardware and CERR planning system are a useful platform for this study. Conflict of Interests: This research was partially supported by a grant from Varian Medical Systems, Inc.

COMPARISON OF ISODOSE DISTRIBUTIONS IN CANINE BRAIN IN HETEROGENEITY‐CORRECTED VERSUS UNCORRECTED TREATMENT PLANS USING 6 MV PHOTONS

Magnetic resonance (MR) images may be useful for radiation planning due to greater contrast resolution. One disadvantage of MR images for radiation planning is the inability to incorporate electron density information into the dose calculation algorithm. To assess the magnitude of this problem, we evaluated radiation dose distribution in canine brain by comparing computed tomography (CT)-based radiotherapy plans with and without electron density correction. Computerized radiotherapy plans were generated for 13 dogs with brain tumors using 6 MV photons. A tissue-contouring program was used to outline the gross tumor volume (GTV) and the planning target volume (PTV) for each patient. Two treatment plans were generated for each dog. First, the plan was optimized without heterogeneity correction. Then the heterogeneity correction was implemented without changing any other plan parameters. Isodose distributions and dose volume histograms (DVHs) were used to compare the two plans. The D95 (dose delivered to 95% of the volume) within the PTV was calculated for each treatment plan and differences in the D95s were compared. The mean D95s without and with heterogeneity correction were 49.1 +/- 0.7 and 48.9 +/- 1.0Gy, respectively. The absolute mean percent dose difference without and with heterogeneity correction was 1.0 - 0.9% (-1.3-3.2%) and was not considered to be clinically significant. We found no clinically significant difference between CT-based radiotherapy plans without and with heterogeneity correction for brain tumors in small animals, which supports the use of MR-based treatment planning for radiotherapy of small animal brain tumors.