Optimal use of radiation therapy for the treatment of animal tumors necessitates accurate clinical evaluation, diagnostic imaging, and pathology. This requires a coordinated effort between the clinical and radiation oncologist, radiologist, and pathologist. The histological appearance of the tumor, tumor grade, and tumor stage are important diagnostic criteria that need to be established. Diagnostic imaging, including radiographic, computerized to-mographic, magnetic resonance imaging, and ultrasoundstudies are helpful in establishing an accurate tumor location and diagnosis. Biopsy and histological examination of tumor tissue are necessary for final diagnosis of tumor type. Determination of tumor type is critical because different tumor types varyin regard to radiosensitivity, local behavior, and propensity for regional and systemic metastasis. The histological grade of many tumors is an important indicator of the potential for local invasion or systemic me-tastases, and may influence treatmentresponse. Tumor staging as determined by clinical evaluation, imaging studies, and histological evaluation is necessary to establish the extent of the tumor, both locally, regionally, and systemically. The clinical oncologist should have an understandingof the procedures involved in tumor diagnosis, tumor grading, and tumor staging. This provides a better understanding of the neoplastic condition and recognition of the limitations of diagnostic procedures. Tumor type, grade, and stage all impact radiation treatment planning and the need for adjuvant regional or systemic therapy.
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