High dose hypofractionated frameless volumetric modulated arc radiotherapy is a feasible method for treating canine trigeminal nerve sheath tumors

Radiation Therapy for Brain Tumors in Dogs and Cats

External beam radiation therapy (RT) has become the standard of care for non-resectable or post-operative incompletely excised brain tumors in dogs and cats due to its relatively low side effect profile and increasing availability. This article reviews the indications for, expected outcomes of and possible toxicities associated with RT, follow-up care recommendations after RT, and publications about specific tumor types in dogs and cats with brain tumors.

Update in Veterinary Radiation Oncology: Focus on Stereotactic Radiation Therapy

Stereotactic radiotherapy (SRT) involves the precise delivery of highly conformal, dose-intense radiation to well-demarcated tumors. Special equipment and expertise are needed, and a unique biological mechanism distinguishes SRT from other forms of external beam radiotherapy. Families find the convenient schedules and minimal acute toxicity of SRT appealing. Common indications in veterinary oncology include nasal, brain, and bone tumors. Many other solid tumors can also be treated, including spinal, oral, lung, heart-base, liver, adrenal, and prostatic malignancies. Accessibility of SRT is improving, and new data are constantly emerging to define parameters for appropriate case selection, radiation dose prescription, and long-term follow-up.

Clinical Findings and Outcome in 30 Dogs with Presumptive or Confirmed Nerve Sheath Tumors

Nerve sheath tumors (NSTs) are well-recognized primary nervous system tumors, but there is relatively limited information in dogs including comparison of NSTs in different anatomical locations. This retrospective study describes the clinical features and outcomes in a group of dogs with NSTs affecting the cranial nerves or spinal nerves. Thirty dogs were included, 25 with a presumptive diagnosis and five confirmed by histopathologic analysis. Seven dogs also had cytology of tumor samples, which were supportive of the NST diagnosis in four. Eight dogs had cranial nerve-associated NSTs, with six involving the trigeminal nerve. Twenty-two dogs had spinal nerve-associated NSTs including 13 invading the spinal canal and nine peripheral to the spinal canal, with the majority affecting nerves or nerve roots of the brachial plexus. The prognosis was poor, with dogs being euthanized eventually because of disease progression. Among dogs alive 1 week after diagnosis, the median survival time was 4 months but ranged from 2 weeks to >2 years. While there was a broad overlap between NST locations, survival was generally longer for dogs without spinal canal or intracranial involvement. The results expand available information on NSTs in dogs but should be interpreted with caution given the small number of dogs with a definitive diagnosis. Further investigation is warranted to determine how tumor location, invasiveness, and treatments pursued impact outcome.

Can volumetric modulated arc radiation therapy reduce organ at risk dose in stage 4 sinonasal tumors in dogs treated with boost irradiation?

Intensity modulated radiation therapy (IMRT) introduced marked changes to cancer treatment in animals by reducing dose to organs at risk (OAR). As the next technological step, volumetric modulated arc therapy (VMAT) has advantages (increased degrees-of-freedom, faster delivery) compared to fixed-field IMRT. Our objective was to investigate a possible advantage of VMAT over IMRT in terms of lower OAR doses in advanced-disease sinonasal tumors in dogs treated with simultaneously-integrated boost radiotherapy. A retrospective, analytical, observational study design was applied using 10 pre-existing computed tomography datasets on dogs with stage 4 sinonasal tumors. Each dataset was planned with both, 5-field IMRT and 2 arc VMAT with 10x4.83 Gy to the gross tumor volume and 10x4.2 Gy to the planning target volume. Adequate target dose coverage and normal tissue complication probability of brain ≤5% was required. Dose constraints aspired to were D60 <15 Gy for eyes, D2 <35.4 Gy for corneae, and Dmean <20 Gy for lacrimal glands. OAR dose was statistically significantly higher in IMRT plans than in VMAT plans. Median eye D60% was 18.5 Gy (interquartile range (IQR) 17.5) versus 16.1 Gy (IQR 7.4) (p = 0.007), median lacrimal gland dose 21.8 Gy (IQR 20.5) versus 18.6 Gy (IQR 7.0) (p = 0.013), and median cornea D2% 45.5 Gy (IQR 6.8) versus 39.9 Gy (IQR 10.0) (p<0.005) for IMRT versus VMAT plans, respectively. Constraints were met in 21/40 eyes, 7/40 corneae, and 24/40 lacrimal glands. Median delivery time was significantly longer for IMRT plans than for VMAT plans (p<0.01). Based on these results, VMAT plans were found to be superior in sparing doses to eyes, lacrimal glands, corneae. However, not all ocular OAR constraints could be met while ensuring adequate dose coverage and restricting brain toxicity risk for both planning techniques.

Unexpected but transient tumour enlargement preceded complete regression and long-term control after irradiation of squamous cell carcinoma in a red-eared slider (Trachemys scripta elegans)

A red-eared slider with a chronic non-healing ulcerative shell lesion was diagnosed with cutaneous squamous cell carcinoma (SCC). The animal underwent surgical debulking, and adjuvant hypofractionated radiation therapy. The lesion initially responded, with near complete tumour regression, but then began growing again just a few months after finishing radiotherapy. Then, after several months with no additional tumour-directed therapy, the lesion again regressed. Five years post-irradiation and with no further treatment, the turtle now remains tumour-free. This unusual pattern of disease regression followed by transient growth and then long-term local tumour control suggests either spontaneous remission, or a pseudoprogression-like phenomenon. Careful clinical follow-up and reporting of future cases will aid in determining whether this pseudoprogression-like event was random, versus being a common component of the chelonian response to irradiation of cutaneous SCC.

Clinical findings and outcome of dogs with unilateral masticatory muscle atrophy

BACKGROUND

Little is known about the spectrum of underlying disorders in dogs with unilateral masticatory muscle (MM) atrophy.

OBJECTIVES

To evaluate the clinical presentation, magnetic resonance imaging (MRI) findings, and outcome of dogs with unilateral MM atrophy.

ANIMALS

Sixty-three client-owned dogs.

METHODS

The medical database was retrospectively reviewed for dogs that underwent MRI for evaluation of unilateral MM atrophy. Imaging studies were reviewed and follow-up information was obtained from telephone interviews.

RESULTS

Presumptive trigeminal nerve sheath tumor (pTNST) was diagnosed in 30 dogs (47.6%); survival time varied from 1 day to 21 months (median, 5 months). Other extra-axial mass lesions were observed in 13 dogs (20.6%); survival time varied from 6 days to 25 months (median, 2.5 months). In 18 dogs (28.6%), no abnormalities were observed on MRI; neurological signs only progressed in 1 dog. Diagnosis had a significant influence on the type of neurological abnormalities, with additional neurological deficits observed in most dogs with pTNST and in all dogs with other extra-axial mass lesions. Diagnosis had a significant effect on euthanasia at the time of diagnosis and likelihood of neurological deterioration. Dogs with mass lesions were more likely to be euthanized or experience neurological deterioration, whereas these outcomes occurred less often in dogs in which no causative lesion could be identified.

CONCLUSIONS AND CLINICAL IMPORTANCE

Trigeminal nerve sheath tumors should not be considered the only cause of unilateral MM atrophy. Our results illustrate the importance of performing a neurological examination and MRI when evaluating dogs with unilateral MM atrophy.

Analysis of radiosensitivity of cancer stem-like cells derived from canine cancer cell lines

Cancer stem-like cells (CSCs) are self-renewing cells comprising a small subpopulation in tumours, and generate differentiated progeny through asymmetric division. It has been shown that CSCs are resistant to ionizing radiation, and this feature could be one of the mechanisms of tumour recurrence after radiation therapy. Much attention has been focused on to target CSCs; however, difficult of isolating CSCs and lack of knowledge on their radiosensitivity have limited this kind of research in veterinary medicine. In the present study, sphere-forming cells (SC), cultured using sphere formation method, were isolated from four type of canine tumour cell lines and evaluated if they have CSCs-like properties by expression of CSCs markers (real-time polymerase chain reaction) and capacity of tumorigenesis (xenograft transplantation in nude mice), and were assessed radiosensitivity (clonogenic survival assay) and DNA repair kinetics (immunofluorescence staining for p53-binding protein 1) after X-ray irradiation in comparison with the corresponding normal adherent culture cells (AC). All SCs were isolated using sphere formation and showed high gene expression of CD133 and tumorigenic ability as compared with AC. All SCs were significantly resistant against X-ray irradiation as compared with AC. In addition, the amount of DNA double-strand breaks after X-ray irradiation were significantly lower in SC compared with the corresponding AC. These results indicate that SC isolated through sphere formation possess CSCs-like characteristics and CSCs are important factor that affect radiosensitivity in canine tumours. In addition, radioresistance of CSCs may depend on reaction of DNA double-strand break after X-ray exposure.