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Clinical Oncology for Medical Dosimetrists

Clinical Oncology for Medical Dosimetrists. DOS 431/531 University of Wisconsin – La Crosse. Nasopharynx. Epidemiology. Uncommon in most countries Highest incidence: China, Southeast Asia, and in Eskimos Peaks in 4 th -5 th decade of life 3 major etiologic factors:

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Clinical Oncology for Medical Dosimetrists

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  1. Clinical Oncology for Medical Dosimetrists DOS 431/531 University of Wisconsin – La Crosse

  2. Nasopharynx

  3. Epidemiology • Uncommon in most countries • Highest incidence: China, Southeast Asia, and in Eskimos • Peaks in 4th-5th decade of life • 3 major etiologic factors: • Viral: Ebstein-Barr virus (EBV) • Genetic: human leukocyte antigen (HLA) • Environmental: poor ventilation, occupational exposures to smoke or dusts, and diet

  4. Anatomy • The nasopharynx is a roughly cuboidal, open chamber located below the base of the skull and behind the nasal cavity. • Borders of the nasopharynx: • Ant. border: posterior choanae • Post. border: first 2 cervical vertebrae and the clivus • Sup. border: body of the sphenoid • Inf. border: soft palate

  5. Anatomy Cont. Nasopharynx

  6. Pathology and Lymphatics • Epidermoid or undifferentiated carcinomas make up about 90% of malignant nasopharynx tumors • Lymphoma, plasmacytoma, melanoma, rhabdomysarcoma, chordoma, and tumors of minor salivary gland origin make up the remaining 10% • Commonly involved lymph nodes: • Cervical lymph nodes • Jugulodigastric lymph nodes • Supraclav nodes

  7. Staging and Management • Many staging systems may be used; however, the most common system used is the TNM staging system. See Table in Chao • Radiation therapy is the treatment of choice for nasopharynx tumors • Chemoradiotherapy has shown to increase survival as well • Surgical resection with acceptable margins is not possible

  8. Radiation Therapy Techniques • Opposed lateral fields with a 5 degree posterior angle (to help avoid direct ipsilateral dose to the external and middle ear, as well as the contralateral lens) • Volumes included: nasopharynx, adjacent parapharyngeal tissues, cervical lymphatics (jugular, spinal accessory, and supraclav nodes), post. ethmoid cells, sphenoid sinus, and basosphenoid, base of skull, post. nasal cavity and maxillary antrum, and lateral and post. pharyngeal wall to the lower pole of tonsil, in addition to the retropharyngeal, upper cervical, mastoid, and posterior cervical lymph nodes • Bilateral anterior supraclav field is always included • Midline block is used

  9. Radiation Therapy Techniques Cont. Field Borders • Ant: posterior 2cm of nasal cavity; posterior 1/3 of maxillary sinus; posterior ethmoid sinuses; posterior ¼ of orbit • Post: behind spinous processes • Sup: entire sphenoid sinus; cavernous sinus; base of skull • Inf: thyroid notch or above the larynx

  10. Radiation Therapy Techniques Cont. Field Borders

  11. Radiation Therapy Techniques Cont. Doses • Full field dose: 45Gy • Reduce fields and use 9MeV electrons to take post. neck nodes to 50-60Gy • Nasopharynx: 65-75Gy • Last 20-25Gy may use high-energy photons (18MV) to reduce dose to the mandible and TMJ • Low neck and supraclav fossa: 50Gy

  12. Radiation Therapy Techniques Cont. Brachytherapy • Brachytherapy can be used to treat nasopharyngeal tumors. • These can be interstitial or intracavitary implants. • More recently, HDR afterloading units have been used to treat intracavitary nasopharynx tumors.

  13. Radiation Therapy Techniques Cont. Nasopharynx Brachytherapy HDR technique

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