The value of magnetic resonance imaging in treatment planning of nasopharyngeal carcinoma.

Seven patients with AJCC Stage T4 nasopharyngeal carcinoma underwent both computed tomographic (CT) and magnetic resonance (MR) examinations prior to radiation therapy treatment planning. Lateral tumor extension into the infratemporal fossa was visualized by MR as less extensive in three cases than suggested by CT, as was inferior extension into the parapharyngeal soft tissues in three cases. MR clarified uncertainties on CT regarding involvement of the pontine cistern in three patients and of the cavernous sinus in two patients. Posterior extension of tumor was underestimated by CT in four of six cases shown by MR to involve the clivus. MR appeared superior in evaluating the presence of parenchymal brain involvement in three cases. The margins of the final boost treatment fields dictated by MR findings differed measurably from those derived from CT in six of seven cases. These findings lend support for greater utilization of MR in treatment planning of nasopharyngeal carcinoma.