THE EMERGING ROLE OF ADVANCED RADIATION THERAPY FOR HEAD AND NECK CANCER

摘要

Canine and feline head and neck tumors present a therapeutic challenge. The PET/CT, IMRT, and SRT were introduced in the previous lecture. This session will include specific application of these technologies to specific tumor types and locations.Tumors of the paranasal sinuses and nasal cavity make up 1% of all canine cancers. Carcinomas, including adeno-, solid- and squamous cell, represent 60% of these tumors. Sarcomas, including fibro-, chondro-, and osteosarcoma make up approximately 30%. Other tumor types, such as lymphoma, mast cell tumor, transmissible venereal tumor, hemangiosarcoma, neuroendocrine tumors and histiocytic sarcomas are seen less commonly. Most nasal tumors are locally invasive and generally have not metastasized at the time of diagnosis. These tumors occur most commonly in middle to older dogs, and dolichocephalic breeds may be over represented. Clinical signs include intermittent and progressive history of unilateral or bilateral mucopurulent discharge or epistaxis. Neurological signs may occur in cases with lysis of the cribiform plate and tumor extension into the cranial vault. Cross-sectional imaging with MR or CT can be pathognomonic for the presence of a tumor, however histological confirmation, generally using endoscopy or transnasal techniques are necessary for tumor histological identification. Most of these tumors are not surgically resectable, and traditional fractionated radiation therapy has long been the primary treatment modality used for these tumors. Reported survival times range from 8-20 months, although tumors causing cribiform lysis with extension into brain are associated with a poor outcome. Over the last 2 decades most radiation therapy centers have treated these tumors with a technique called3 dimensional conformal radiation therapy (3D-CRT). This technique results in a high level of certainly that the tumor receives the prescribed dose. However, there is limited ability to minimize dose to surrounding normal tissues such as the eyes, skin,tongue, and mucous membranes of the oral cavity. Therefore the technique is associated with severe acute radiation effects. Although these effects will resolve with time and supportive care, the patients are often extremely uncomfortable and rigorous pain management is required. So despite the efficacy of the treatment, many owners bypass radiation therapy in favor of more palliative techniques.