Familial Nasopharyngeal Carcinoma 6

260 W. I. Weiradiation dose is highest at the source and declinesgradually, proportional with increasing distance fromthe tumor. This thus allows the delivery of a high therapeuticradiation dose to the residual or recurrentNPC while the surrounding tissues receive a muchsmaller dose. The radiation source in brachytherapyalso delivers radiation at a continuous rate and this isbiologically more effective than the fractionatedexternal radiation doses. Intracavitary brachytherapyhas been used for the treatment of NPCs either as aboost with the primary treatment or as therapeutictreatment for residual or recurrent disease (Wanget al. 1975). The radiation source was placed either ina tube or a mould and then inserted into the nasopharynxto be placed close to tumor. Good result wasachieved with this form of intracavitary brachytherapy(Law et al. 2002). The limitation of this form ofintracavitary brachytherapy is the irregular contourof the primary tumor located within the nasopharynxthat by itself does not have a uniform outline. It is difficultto apply the radiation source accurately into thevicinity of the whole tumor to obtain a tumoricidaldose. To circumvent this problem, radioactive interstitialimplants inserted directly into the tumor havebeen used to treat small localized residual or recurrenttumor in the nasopharynx (Harrison andWeissber 1987).One of the frequently used brachytherapy sourceis the radioactive gold grains ( 198 Au). These goldgrains can be implanted directly into the tumor eithertransnasally with endoscopic guidance or using thesplit-palate approach (Wei et al. 1990b). The splitpalateapproach provides a direct view of the tumorfor the surgeon and the oncologist (Fig. 20.12). Thisenables the implantation of the appropriate numberof gold grains permanently into the tumor with precision(Fig. 20.13). This enables the exact dosimetryof radiation to be achieved in and around the tumorfor the salvage purpose. For tumors localized in thenasopharynx, without bone invasion, this methodhas provided effective and high rate of salvage withminimal morbidity. The surgical procedure is simpleFig. 20.12. The soft palate was split in the midline and togetherwith the mucoperiosteum over the hard palate were retractedlaterally. The black tip of a flexible endoscope ( arrow) was insertedthrough the nose to provide better illumination. Theedge of a shallow tumor could be seen ( arrow heads)Fig. 20.13. Skull X-ray showing the inserted gold grains (arrows)