Advances in Radiation Therapy for Nasal Tumors

Chapter 74

Advances in Radiation Therapy for Nasal Tumors

Nasosinal tumors always have presented a therapeutic challenge. Surgery alone rarely is an option due to local macroscopic and microscopic extension to critical normal tissue structures, and combining surgery with radiation therapy has not uniformly improved treatment outcome. Chemotherapy, including the use of nonsteroidal antiinflammatory drugs, has been reported as a palliative option. Radiation therapy long has been considered the standard of care despite the significant acute effects associated with treatment. Disappointingly, the collective median survival times for patients treated with radiation therapy have not improved since early data were reported in the 1980s.

The introduction of two new radiation-associated technologies now available in veterinary medicine already has decreased acute radiation effects in these patients, and ongoing work is evaluating the impact on long-term tumor control. These technologies are (1) intensity-modulated radiation therapy (IMRT), which, by using inverse treatment-planning algorithms, allows for more precise application of radiation dose to the tumor and preferentially spares adjacent normal tissue structures in the region; and (2) stereotactic radiation therapy (SRT), which delivers curative-intent radiation therapy according to protocols that require only one to five fractions. This chapter focuses on treatment advances associated with these technologies.

Pathologic Features and Clinical Presentation

Nasosinal tumors represent 1% of all canine neoplasia. Carcinomas, including adenocarcinomas, solid tumors, and squamous cell carcinomas, represent 60% of these tumors; sarcomas, including fibrosarcomas, chondrosarcomas, and osteosarcomas, make up approximately 30% of all nasal tumors. Lymphoma, mast cell tumors, transmissible venereal tumors, hemangiosarcomas, neuroendocrine tumors, and histocytic sarcomas are seen less frequently. Most nasal tumors are locally invasive and generally have not metastasized at the time of diagnosis. These tumors occur most commonly in middle-aged to older dogs, and dolichocephalic breeds may be overrepresented. Clinical signs include intermittent and progressive history of unilateral or bilateral mucopurulent discharge or epistaxis. Stertorous breathing, sneezing, reverse sneezing, and dyspnea can be observed. Facial deformity caused by bone erosion and tumor extension outside of the bone as well as exophthalmos also can be seen. Neurologic signs may occur in cases with lysis of the cribriform plate and tumor extension into the cranial vault. Initial signs may respond to antibiotics or steroids, which can prolong the time until an accurate diagnosis is established.

Diagnostic Approach

Differential diagnoses include fungal or bacterial infection, lymphocytic-plasmacytic rhinitis, bleeding disorders, and foreign bodies. Nasal radiographs may define changes in the nasal cavities and sinuses, but cross-sectional imaging (computed tomography [CT] or magnetic resonance imaging [MRI]) is preferred. Histologic confirmation is required for definitive diagnosis, although classic changes observed on CT or MRI scans combined with history and clinical signs are highly suggestive. The patient should be evaluated for potential coagulopathies before biopsy because postprocedure bleeding can be significant. The CT or MRI should be performed before biopsy to identify the optimal site from which to procure a specimen and to prevent postbiopsy bleeding from complicating the interpretation of the imaging study. A number of biopsy techniques have been described in the literature. Transnostril techniques are advantageous because they do not create a biopsy track that will have to be addressed if the patient is to be treated with surgery or radiation therapy. When this technique is used, one should make sure that the biopsy instrument is marked so that it penetrates no further than the medial canthus, which minimizes the risk to the cribriform plate and brain. Rhinoscopic techniques are minimally traumatic; however, even experienced operators can be frustrated by the inability to obtain a sample of sufficient quality and quantity for diagnosis. Nasal hydropulsion was reported recently as a minimally invasive technique that yielded samples from which a definitive diagnosis could be made in 90.2% of attempts (Ashbaugh et al, 2011). Although these tumors are unlikely to have metastatic spread, thoracic radiographs should be included in staging if radiation therapy is being considered as a treatment option.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Advances in Radiation Therapy for Nasal Tumors
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