The oropharynx has a rich lymphatic plexus draining for the most part to the upper anterior cervical or subdigastric lymph nodes.
3 Pathology The vast majority of oropharyngeal cancers are well to poorly differentiated squamous cell carcinomas. Cancers of other types, as lymphomas and melanomas, are not suitable for interstitial irradiation. Lymphatic metastasis, whose frequency correlates with the size and degree of infiltration of the primary tumour, is noted at presentation in up to 80% of patients and is often bilateral. Work Up All patients undergoing irradiation for oropharyngeal cancer require a detailed examination of the head and neck region as well as a thorough general physical examination and the assessment of the clinical stage according to the UICC-TNM classification. In addition, routine blood examination is made and a chest radiograph and an electrocardiogram taken. An examination under general anaesthesia, preferably in combination with a panendoscopy of the higher respiratory and digestive tract, in order to rule out synchronous second primary tumours, is made. This includes bronchial and oesophageal examination with brushing cytological tests, a vital staining with toluidine blue and biopsies of any lesion. If brachytherapy is considered as a boost modality after initial external beam irradiation, it is useful to tattoo the limits of the gross disease during this endoscopy. MRI is the best imaging procedure for determination of tumour volume and extension. CT scan and cervical ultrasonography are both useful for diagnosis of metastatic cervical nodes. Indications, Contra-indications Iridium LDR, HDR or PDR interstitial implantation may be indicated in the treatment of squamous cell carcinoma of the base of tongue, the soft palate, the tonsillar fossa, and the vallecula. Tumours must be less than 50 mm in diameter. Implantation is contraindicated if the primary tumour extends to the retromolar trigone, the nasopharynx, the larynx, the hypopharynx, or if the lesion is fixed to the underlying structures or invades bone. Implantation is usually not performed when the primary tumour is associated with bulky cervical lymph nodes. Because of the high incidence of cervical lymph node metastases, which are present in more than one half of patients, brachytherapy is usually delivered as a boost after 45 - 50 Gy external beam radiation therapy to both primary tumour and cervical neck node areas. Brachytherapy alone may be used only for purely exophytic tumours, 10 mm or less in diameter, and in recurring cancers or new tumour arising in previously irradiated territory. Target Volume The clinical target volume for well-delineated squamous cell carcinoma is the palpable and visible tumour (including extensions visible on CT or MRI) before any treatment, with a safety margin of at 4 5 6
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