Impact of magnetic resonance imaging versus CT on nasopharyngeal carcinoma: primary tumor target delineation for radiotherapy.

Background: Our aim was to assess the capacity of CT versus MRI for delineating to the primary tumor extent of nasopharyngeal carcinoma (NPC) in treated patients.

Methods: From December 1997 to April 2000, 258 patients with NPC were enrolled. We focused on the primary tumor extension and the discrepancy between CT and MRI. The delineation of tumor invasion was crucial for determination of the gross tumor volume (GTV) before radiation therapy.

Results: A total of 104 patients (40.3%) had intracranial infiltration detected by MRI, whereas CT showed negative findings (p = 6.879 x 10(-11)). Once the pterygopalatine fossa was involved, the chance of intracranial invasion was increased (96.1%). The detectable percentage of pterygopalatine fossa involvement accompanying intracranial invasion was higher with MRI than with CT (96.1% vs 56.9%).

Conclusions: More detailed information about T and N classification of NPC was provided by MRI than by CT, which led to better target delineation for radiotherapy.