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  • Successful palliative radiation therapy for locally advanced and metastatic nasal carcinoma in a cat

    Dr. Cassandra Wilcox, DVM, DACVR (RO)

    BACKGROUND: A 14-year-old male castrated Domestic Shorthair cat was presented to the emergency service at a large referral center for evaluation of nasal discharge and swelling over the nose. On presentation mucoid nasal discharge with epistaxis was present bilaterally, along with a severe facial deformity. Skull radiographs showed significant bone destruction along the bridge of the nose. A fine needle aspirate was performed over the bridge of the nose and cytology confirmed a diagnosis of carcinoma with neutrophilic inflammation. A nasal culture was negative. Consultation with medical oncology was pursued and staging diagnostics (thoracic radiographs, CBC, Chemistry, UA) showed no evidence of pulmonary metastatic disease and mild pre-renal azotemia.

     

    Figure 1. Axial CT image at the level of the canine teeth. Marked left sided maxillary bone lysis is present, along with a contrast enhancing mass filling the left and right nasal cavity and extending out of the defect into the surrounding tissues.

    A CT was performed of the head and neck which revealed a large contrast enhancing soft tissue mass almost completely filling the left and right rostral nasal cavity. Marked maxilloturbinate destruction as well as mild right sided maxillary bone lysis and marked left sided maxillary bone lysis was present with the contrast enhancing mass extending outward through the large region of lysis in the left maxilla causing marked bulging to the contour of the muzzle (Figure 1). The mass extended caudally to cause moderate ethmoturbinate destruction and minimal lysis of the rostral extent of the cribriform plate. The mandibular and medial retropharyngeal lymph nodes were moderately enlarged and heterogeneously contrast enhancing. A fine needle aspirate of both mandibular lymph nodes was performed, and cytology confirmed metastasis to the left mandibular lymph node.

    Given the presence of metastasis and severity of the local disease, palliative radiation therapy was elected by the owner. Palliative, or hypofractionated radiation therapy is a short course of radiation therapy offered to patients for a variety of reasons, including but not limited to: advanced disease, poor prognosis, significant comorbidities that preclude daily anesthesia, owner goals, etc. The aims of palliative radiation are to reduce discomfort related to a tumor and/or to reduce the size of a tumor for a short period of time to improve quality of life. Palliative radiation therapy is delivered with a traditional linear accelerator. The proximity of the tumor to many critical structures makes treatment without significant morbidity challenging in the treatment of nasal tumors. Intensity modulated radiation therapy (IMRT) is utilized in this setting to improve radiation dose to the tumor while sparing normal critical structures. IMRT is a new technology in radiation oncology that delivers radiation more precisely to the tumor while relatively sparing the surrounding normal tissues, essentially “painting” doses of radiation to a target (the tumor). IMRT has wide application in most aspects of radiation oncology because of its ability to create multiple targets and avoid critical structures. By delivering radiation with greater precision, IMRT has been shown to minimize acute treatment-related side effects, which further improves patient comfort during and after treatment.  IMRT utilizes multileaf collimators, which are made up of individual “leaves” of a high atomic numbered material, usually tungsten that can move independently in and out of the path of radiation in order to block portions of the beam and thus custom-shape the patient’s radiation field.

     

    TREATMENT: Radiation treatment planning was performed based on the CT images for this patient. The nasal tumor and enlarged lymph nodes were identified as the target (PTV), and organs at risk (OAR) were also identified, including the left and right eye, brain, left and right inner ear, and spinal cord. Dose constraints to the OARs were set based upon known tolerance levels of these organs and a minimum dose to the target was set such that 90% of the target received 100% of the prescribed radiation dose (Figure 2).

    Figure 2. Axial (A) and sagittal (B) images of a 7-field IMRT plan. The dose color wash in blue/green shows the intended target (PTV) receiving 90% and above of the prescribed radiation dose. The specified organs at risk (OARS), including the eyes, brain, and spinal cord are spared from high doses of radiation by utilization of an IMRT technique.

    The radiation treatments were delivered in 4 fractions, or treatments, given weekly over 4 weeks. The total radiation dose delivered was 32 Gy. For each treatment, the patient was anesthetized with a combination of Methadone and Propofol and placed in sternal recumbency in a vacuum-deformable mattress. Orthogonal kilovoltage radiographs (or port films) were performed at each treatment and the treatment couch was then moved based on these images to place the patient in the correct position for treatment. Each anesthesia and treatment were completed without complication. At each subsequent treatment after the first, the facial deformity was visibly improved. By the end of the course of radiation therapy, the patient was markedly improved with airflow through both nostrils. A small amount of hair loss was noted on the bridge of the nose at the end of treatment, but no other radiation side effects were noted.

     

    RELEVANCE:  Lymphoma is the most commonly diagnosed nasal tumor in cats, followed second by those of epithelial origin (carcinomas). Generally, these tumors are locally invasive with a low metastatic rate at the time of diagnosis, making radiation therapy the treatment of choice for nasal tumors.1 Only 2 reports exist documenting the use of radiation for non-lymphoproliferative nasal tumors in cats. In one report, cats received a definitive course of radiation therapy (total dose of 48 Gy), and the reported median survival time (MST) was 12 months.2 In another smaller report, cats were treated with a palliative course of radiation therapy with a reported MST of almost 13 months.3 The presence of metastasis at presentation in this case would be anticipated to negatively impact survival but is ultimately unknown. This case shows the utility of both IMRT for nasal tumors in decreasing acute side effect morbidity and for effective palliation of clinical signs secondary to a large and invasive nasal tumor. Various treatment options are available for the management of nasal tumors, thus a board-certified radiation oncologist should be consulted about the most appropriate treatment type for each patient.

     

    REFERENCES:

    1. Page, R. L., Vail, D. M., & Withrow, S. J. (2013). Withrow and MacEwens Small Animal Clinical Oncology. W.B. Saunders. Pgs 446-447.
    2. Theon AP, Peaston AE, Madewell BR, et al: Irradiation of nonlymphoproliferative neoplasms of the nasal cavity and paranasal sinuses in 16 cats, J Am Vet Med Assoc 204:78-83, 1994. http://europepmc.org/abstract/med/8125825
    3.  Mellanby RJ, Herrtage ME, Dobson JM: Long-term outcome of eight cats with non-lymphoproliferative nasal tumours treated by megavoltage radiotherapy, J Feline Med Surg 4:77-81, 2002. http://journals.sagepub.com/doi/abs/10.1053/jfms.2001.0159

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