PET/CT FOLLOWING INTENSITY-MODULATED RADIATION THERAPY FOR PRIMARY LUNG TUMOR IN A DOG

The Importance of the Tumor Microenvironment and Hypoxia in Delivering a Precision Medicine Approach to Veterinary Oncology

Treating individual patients on the basis of specific factors, such as biomarkers, molecular signatures, phenotypes, environment, and lifestyle is what differentiates the precision medicine initiative from standard treatment regimens. Although precision medicine can be applied to almost any branch of medicine, it is perhaps most easily applied to the field of oncology. Cancer is a heterogeneous disease, meaning that even though patients may be histologically diagnosed with the same cancer type, their tumors may have different molecular characteristics, genetic mutations or tumor microenvironments that can influence prognosis or treatment response. In this review, we describe what methods are currently available to clinicians that allow them to monitor key tumor microenvironmental parameters in a way that could be used to achieve precision medicine for cancer patients. We further describe exciting novel research involving the use of implantable medical devices for precision medicine, including those developed for mapping tumor microenvironment parameters (e.g., O2, pH, and cancer biomarkers), delivering local drug treatments, assessing treatment responses, and monitoring for recurrence and metastasis. Although these research studies have predominantly focused on and were tailored to humans, the results and concepts are equally applicable to veterinary patients. While veterinary clinical studies that have adopted a precision medicine approach are still in their infancy, there have been some exciting success stories. These have included the development of a receptor tyrosine kinase inhibitor for canine mast cell tumors and the production of a PCR assay to monitor the chemotherapeutic response of canine high-grade B-cell lymphomas. Although precision medicine is an exciting area of research, it currently has failed to gain significant translation into human and veterinary healthcare practices. In order to begin to address this issue, there is increasing awareness that cross-disciplinary approaches involving human and veterinary clinicians, engineers and chemists may be needed to help advance precision medicine toward its full integration into human and veterinary clinical practices.

A retrospective analysis of radiation oncology related scientific articles in the journal Veterinary Radiology and Ultrasound: Trends over 40 years (1976-2015)

The journal Veterinary Radiology & Ultrasound is a veterinary specialty journal devoted to the fields of veterinary diagnostic imaging and radiation oncology. The purpose of this retrospective, observational study is to evaluate progressive trends in radiation oncology articles published in Veterinary Radiology & Ultrasound during the 40-year period (1976-2015) and describe a shift of trends through several viewpoints. This 40-year period was divided into four subperiods: Period 1 (1976-1985), Period 2 (1986-1995), Period 3 (1996-2005), and Period 4 (2006-2015). These articles were divided into six categories based on the nature of the study: 1) studies related to teletherapy with endpoints being patient outcome, 2) radiation therapy dosimetry/planning, 3) patient setup, 4) reviews, 5) case reports, and 6) others. The number of radiation oncology articles in Veterinary Radiology & Ultrasound has increased over the 40-year period. The number of authors per article has increased between Periods 1 and 3. The number of articles related to linear accelerator has increased between Periods 3 and 4. The median number of treated patients per clinical article related to teletherapy ranged from 15 to 21, which has not changed significantly over the 40-year period. The most commonly used radiation therapy protocols during Periods 2 and 3 were fine-fractionated protocols (defined as 10 or more fractions), whereas coarse-fractionated protocols were more common during Periods 1 and 4. Findings from this study highlight the notable changes of trends in veterinary radiation oncology articles published in Veterinary Radiology & Ultrasound, which clearly reflect changes in the field of veterinary radiation oncology during the past 40 years.

Relative skeletal distribution of proliferating marrow in the adult dog determined using 3'-deoxy-3'-[18 F]fluorothymidine

3'-deoxy-3'-[¹⁸ F]fluorothymidine (¹⁸ FLT) is a radiopharmaceutical tracer used with positron emission tomography (PET), often in combination with computed tomography (CT), to image DNA synthesis, and thus, cellular proliferation. Characteristic accumulation of the tracer within haematopoietic bone marrow provides a noninvasive means to assess marrow activity and distribution throughout the living animal. The present study utilizes three-dimensional analysis of ¹⁸ FLT-PET/CT scans to quantify the relative skeletal distribution of active marrow by anatomic site in the dog. Scans were performed on six healthy, adult (3-6 years of age), mixed-breed dogs using a commercially available PET/CT scanner consisting of a 64-slice helical CT scanner combined with an integrated four ring, high-resolution LSO PET scanner. Regions of interest encompassing 11 separate skeletal regions (skull, cervical vertebral column, thoracic vertebral column, lumbar vertebral column, sacrum, ribs, sternum, scapulae, proximal humeri, ossa coxarum, and proximal femora) were manually drawn based on CT images and thresholded by standardized uptake value to delineate bone marrow activity. Activity within each skeletal region was then divided by the total skeletal activity to derive the per cent of overall marrow activity within an individual site. The majority of proliferative marrow was located within the vertebral column. Of the sites traditionally accessed clinically for marrow sampling, the proximal humerus contained the largest percentage, followed by the ossa coxarum, proximal femur, and sternum, respectively. This information may be used to guide selection of traditional marrow sampling sites as well as inform efforts to spare important sites of haematopoiesis in radiation therapy planning.

Use of Molecular Imaging Markers of Glycolysis, Hypoxia and Proliferation ((18)F-FDG, (64)Cu-ATSM and (18)F-FLT) in a Dog with Fibrosarcoma: The Importance of Individualized Treatment Planning and Monitoring

Glycolysis, hypoxia, and proliferation are important factors in the tumor microenvironment contributing to treatment-resistant aggressiveness. Imaging these factors using combined functional positron emission tomography and computed tomography can potentially guide diagnosis and management of cancer patients. A dog with fibrosarcoma was imaged using ¹⁸F-FDG, ⁶⁴Cu-ATSM, and ¹⁸F-FLT before, during, and after 10 fractions of 4.5 Gy radiotherapy. Uptake of all tracers decreased during treatment. Fluctuations in ¹⁸F-FDG and ¹⁸F-FLT PET uptakes and a heterogeneous spatial distribution of the three tracers were seen. Tracer distributions partially overlapped. It appears that each tracer provides distinct information about tumor heterogeneity and treatment response.

Comparative Oncology: Evaluation of 2-Deoxy-2-[18F]fluoro-D-glucose (FDG) Positron Emission Tomography/Computed Tomography (PET/CT) for the Staging of Dogs with Malignant Tumors

Introduction

2-Deoxy-2-[18F]fluoro-D-glucose PET/CT is a well-established imaging method for staging, restaging and therapy-control in human medicine. In veterinary medicine, this imaging method could prove to be an attractive and innovative alternative to conventional imaging in order to improve staging and restaging. The aim of this study was both to evaluate the effectiveness of this image-guided method in canine patients with spontaneously occurring cancer as well as to illustrate the dog as a well-suited animal model for comparative oncology.

Methods

Ten dogs with various malignant tumors were included in the study and underwent a whole body FDG PET/CT. One patient has a second PET-CT 5 months after the first study. Patients were diagnosed with histiocytic sarcoma (n = 1), malignant lymphoma (n = 2), mammary carcinoma (n = 4), sertoli cell tumor (n = 1), gastrointestinal stromal tumor (GIST) (n = 1) and lung tumor (n = 1). PET/CT data were analyzed with the help of a 5-point scale in consideration of the patients’ medical histories.

Results

In seven of the ten dogs, the treatment protocol and prognosis were significantly changed due to the results of FDG PET/CT. In the patients with lymphoma (n = 2) tumor extent could be defined on PET/CT because of increased FDG uptake in multiple lymph nodes. This led to the recommendation for a therapeutic polychemotherapy as a treatment. In one of the dogs with mammary carcinoma (n = 4) and in the patient with the lung tumor (n = 1), surgery was cancelled due to the discovery of multiple metastasis. Consequently no treatment was recommended.

Conclusion

FDG PET/CT offers additional information in canine patients with malignant disease with a potential improvement of staging and restaging. The encouraging data of this clinical study highlights the possibility to further improve innovative diagnostic and staging methods with regard to comparative oncology. In the future, performing PET/CT not only for staging but also in therapy control could offer a significant improvement in the management of dogs with malignant tumors.

PET and SPECT imaging in veterinary medicine

Veterinarians have gained increasing access to positron emission tomography (PET and PET/CT) imaging facilities, allowing them to use this powerful molecular imaging technique for clinical and research applications. SPECT is currently being used more in Europe than in the United States and has been shown to be useful in veterinary oncology and in the evaluation of orthopedic diseases. SPECT brain perfusion and receptor imaging is used to investigate behavioral disorders in animals that have interesting similarities to human psychiatric disorders. This article provides an overview of the potential applications of PET and SPECT. The use of commercially available and investigational PET radiopharmaceuticals in the management of veterinary disease has been discussed. To date, most of the work in this field has utilized the commercially available PET tracer, (18)F-fluorodeoxyglucose for oncologic imaging. Normal biodistribution studies in several companion animal species (cats, dogs, and birds) have been published to assist in lesion detection and interpretation for veterinary radiologists and clinicians. Studies evaluating other (18)F-labeled tracers for research applications are underway at several institutions and companion animal models of human diseases are being increasingly recognized for their value in biomarker and therapy development. Although PET and SPECT technologies are in their infancy for clinical veterinary medicine, increasing access to and interest in these applications and other molecular imaging techniques has led to a greater knowledge and collective body of expertise for veterinarians worldwide. Initiation and fostering of physician-veterinarian collaborations are key components to the forward movement of this field.

A proposed simple model for estimating occupational radiation dose to staff from veterinary 18F-FDG pet procedures

Several studies have been conducted concerning the radiation dose to hospital personnel from positron emission tomography (PET) radiopharmaceuticals, but to date only one parallel study has been conducted for veterinary staff. Veterinary patients present challenges not encountered with human patients, as they require anesthesia and therefore more intensive monitoring than human patients. This paper presents a simple model for estimating the effective radiation dose to veterinary staff using occupational dose data from PET studies at Colorado State University's (CSU) James L. Voss Veterinary Teaching Hospital. The model consists of three point sources within a soft tissue cylinder, and sample calculations are provided for estimating dose to nuclear medicine technologists and an anesthesia technologist based on four different sized dogs. The estimated doses are within the range of actual occupational doses published previously. There are different protocols for the sequence of events in veterinary PET, specifically the order of anesthesia induction and radiopharmaceutical injection. When F-FDG injection is performed prior to anesthesia induction, the estimated dose is between 1.5 and 3.6 times higher than the doses received if injection is done after anesthesia induction, although expected doses for both protocols are below occupational dose limits based on a case load of 100 veterinary patients per year. The model is based on the techniques used at CSU, but it can be modified for different hospitals as well as differently sized animals.

FDG-PET in healthy and epileptic Lagotto Romagnolo dogs and changes in brain glucose uptake with age

Regional cerebral metabolism and blood flow can be measured noninvasively with positron emission tomography (PET). 2-[(18) F]fluoro-2-deoxy-D-glucose (FDG) widely serves as a PET tracer in human patients with epilepsy to identify the seizure focus. The goal of this prospective study was to determine whether juvenile or adult dogs with focal-onset epilepsy exhibit abnormal cerebral glucose uptake interictally and whether glucose uptake changes with age. We used FDG-PET to examine six Lagotto Romagnolo dogs with juvenile epilepsy, two dogs with adult-onset epilepsy, and five control dogs of the same breed at different ages. Three researchers unaware of dog clinical status visually analyzed co-registered PET and magnetic resonance imaging (MRI) images. Results of the visual PET analyses were compared with electroencephalography (EEG) results. In semiquantitative analysis, relative standard uptake values (SUV) of regions of interest (ROI) drawn to different brain regions were compared between epileptic and control dogs. Visual analysis revealed areas of hypometabolism interictally in five out of six dogs with juvenile epilepsy in the occipital, temporal, and parietal cortex. Changes in EEG occurred in three of these dogs in the same areas where PET showed cortical hypometabolism. Visual analysis showed no abnormalities in cerebral glucose uptake in dogs with adult-onset epilepsy. Semiquantitative analysis detected no differences between epileptic and control dogs. This result emphasizes the importance of visual analysis in FDG-PET studies of epileptic dogs. A change in glucose uptake was also detected with age. Glucose uptake values increased between dog ages of 8 and 28 weeks and then remained constant.

Whole-body biodistribution of 3'-deoxy-3'-[(18) f]fluorothymidine ((18) FLT) in healthy adult cats

Positron emission tomography/computed tomography (PET/CT) utilizing 3'-deoxy-3'-[(18) F]fluorothymidine ((18) FLT), a proliferation tracer, has been found to be a useful tool for characterizing neoplastic diseases and bone marrow function in humans. As PET and PET/CT imaging become increasingly available in veterinary medicine, knowledge of radiopharmaceutical biodistribution in veterinary species is needed for lesion interpretation in the clinical setting. The purpose of this study was to describe the normal biodistribution of (18) FLT in adult domestic cats. Imaging of six healthy young adult castrated male cats was performed using a commercially available PET/CT scanner consisting of a 64-slice helical CT scanner with an integrated whole-body, high-resolution lutetium oxy-orthosilicate (LSO) PET scanner. Cats were sedated and injected intravenously with 108.60 ± 2.09 (mean ± SD) MBq of (18) FLT (greater than 99% radiochemical purity by high-performance liquid chromatography). Imaging was performed in sternal recumbency under general anesthesia. Static images utilizing multiple bed positions were acquired 80.83 ± 7.52 (mean ± SD) minutes post-injection. Regions of interest were manually drawn over major parenchymal organs and selected areas of bone marrow and increased tracer uptake. Standardized uptake values were calculated. Notable areas of uptake included hematopoietic bone marrow, intestinal tract, and the urinary and hepatobiliary systems. No appreciable uptake was observed within brain, lung, myocardium, spleen, or skeletal muscle. Findings from this study can be used as baseline data for future studies of diseases in cats.

PET/CT today and tomorrow in veterinary cancer diagnosis and monitoring: fundamentals, early results and future perspectives

Functional imaging using positron emission tomography (PET) plays an important role in the diagnosis, staging, image-guided treatment planning and monitoring of malignant diseases. PET imaging complements conventional anatomical imaging such as computed tomography (CT) and magnetic resonance imaging (MRI). The strength of CT scanning lies in its high spatial resolution, allowing for anatomical characterization of disease. PET imaging, however, moves beyond anatomy and characterizes tissue based on functions such as metabolic rate. Combined PET/CT scanners were introduced commercially in 2001 and a number of technological advancements have since occurred. Radiolabelled tracers such as (18)F-fluorodeoxyglucose (FDG) and (18)F-fluorothymidine (FLT) allow visualization of various metabolic processes within cancer cells. Many studies in human oncology evaluating the utility of PET/CT have demonstrated clinical benefits. Few veterinary studies have been performed, but initial studies show promise for improved detection of malignancy, more thorough staging of canine cancer and determination of early response and disease recrudescence.

¹⁸F-FDG and ¹¹C-MET positron emission tomography findings of cutaneous mast cell tumor in a dog

A 12-year-old intact male Maltese dog presented with an inguinal mass. Histopathology revealed a grade III mast cell tumor. Computed tomography demonstrated pulmonary and inguinal nodules and masses. Chemotherapy was performed using a vinblastine/prednisone protocol, and the inguinal mass disappeared 5 weeks later. Use of 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) and (L)-[methyl- ¹¹C]methionine (¹¹C-MET)-positron emission tomography (PET) demonstrated hypermetabolic areas in the lungs and inguinal region one week after initial chemotherapy. The standardized uptake values of ¹⁸F-FDG were not different between lung and inguinal lesions; however, the inguinal lesion had a higher ¹¹C-MET standardized uptake value than the lung lesions. The hypermetabolic area was still visible on the second ¹⁸F-FDG-PET scan despite the disappearance of the mass. This is the first report of ¹¹C-MET-PET findings associated with a cutaneous mast cell tumor in a dog.

Comparative aspects of the proliferation marker thymidine kinase 1 in human and canine tumour diseases

As cell proliferation is one of the hallmarks of cancer, various types of proliferation markers are used as important tools in diagnosis, prognosis, treatment decision-making and follow-up in clinical oncology. The S phase-specific protein thymidine kinase 1 (TK1) can be used in immunohistochemistry for RNA/protein expression in tissue specimens and for activity or protein/peptide levels in serum from patients. TK1 has been used mainly in haematologic malignancies in humans, but also found beneficial in canine malignancies. As the protein sequence homology is high between humans and dogs, findings in canine models will have a high comparative value in further human research as well. In the present review, we will focus on the recent results concerning TK1's S phase-correlated expression, increased serum levels of TK1 in patients with malignancies and the relevance for veterinary and comparative oncology. Finally, the benefit of recently developed specific anti-TK1 antibodies suitable for immunologic assay is discussed.

Effects of anesthetic protocol on normal canine brain uptake of 18F-FDG assessed by PET/CT

The purpose of this study was to assess the effects of four anesthetic protocols on normal canine brain uptake of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) using positron emission tomography/computed tomography (PET/CT). Five clinically normal beagle dogs were anesthetized with (1) propofol/isoflurane, (2) medetomidine/pentobarbital, (3) xylazine/ketamine, and (4) medetomidine/tiletamine-zolazepam in a randomized cross-over design. The standard uptake value (SUV) of FDG was obtained in the frontal, parietal, temporal and occipital lobes, cerebellum, brainstem and whole brain, and compared within and between anesthetic protocols using the Friedman test with significance set at P < 0.05. Significant differences in SUVs were observed in various part of the brain associated with each anesthetic protocol. The SUV for the frontal and occipital lobes was significantly higher than in the brainstem in all dogs. Dogs receiving medetomidine/tiletamine-zolazepam also had significantly higher whole brain SUVs than the propofol/isoflurane group. We concluded that each anesthetic protocol exerted a different regional brain glucose uptake pattern. As a result, when comparing brain glucose uptake using PET/CT, one should consider the effects of anesthetic protocols on different regions of the glucose uptake in the dog's brain.

Impact of primary tumour stage on survival in dogs with solitary lung tumours

OBJECTIVES

The objective of this study was to determine simple prognostic criteria for differentiation of canine solitary lung tumour cases into those that will and will not benefit from thoracic surgery.

METHODS

This was a retrospective study using the records of cases presented to Davies Veterinary Specialists, Hitchin, UK, from December 1998 to December 2005. Survival analyses were performed using the Kaplan-Meier and logrank methods. Potentially significant variables were evaluated by multivariate Cox analysis.

RESULTS

Forty-two patients met the inclusion criteria. Primary tumour stage T1, absence of neoplastic lymph nodes and metastases, and papillary tumour type were statistically significant favourable prognostic indicators on univariate analysis. Multivariate analysis attributed significance to primary tumour stage T1 and papillary type only. Median survival times were 555 days for T1N0M0 tumours of papillary type and 72 days for the remainder.

CLINICAL SIGNIFICANCE

Survival time following surgery in dogs with primary lung tumours was poor except in clinical stage T1N0M0 cases. These data support use of clinical techniques to dichotomise cases as T1N0M0 or other, improving decision making in thoracic surgery. These data validate initiation of prospective studies examining the role of chemotherapy in the management of advanced cases.

Advanced imaging for veterinary cancer patients

This article presents an update on the recent advances made in veterinary advanced imaging specifically with regard to cross-sectional modalities (CT and MRI) and nuclear medicine (positron emission tomography [PET] and PET/CT). A brief summary of technical improvements and a review of recent literature are included to provide an overview of the progress made in this important element of the practicing veterinary oncologist's repertoire. An in-depth summary of PET is also included to introduce the technical aspects and potential clinical and research applications of this novel imaging modality in veterinary medicine.

Use of [123I]-2-iodo-L-phenylalanine as a tumor imaging agent in two dogs with synovial cell sarcoma

[123I]-iodo-L-phenylalanine was successfully evaluated for gamma camera imaging in vivo in tumor-bearing athymic mice and in humans with brain tumors. Here, we report the use of this tracer in two dogs with synovial cell sarcoma of the tarsus. [123I]-iodo-L-phenylalanine was quantitatively prepared as a kit formulation using the Cu(1+) +-assisted nucleophilic exchange. Rapid [123I]-2-iodo-L-phenylalanine tumor accumulation was observed with good tumor to background contrast and rapid clearance in these two dogs. This radiopharmaceutical is a promising alternative tumor tracer to overcome the known limitations of 18F-fluorodeoxyglucose and, when labelled with radioiodine-131, has the potential to be used for therapeutic purposes.