Radiotherapy for nasopharyngeal carcinoma: shielding the pituitary may improve therapeutic ratio

Nasopharyngeal carcinoma (NPC) is well known for its invasiveness and erosion of the base of the skull is not uncommon. Before the advent of computed tomography, the evaluation of the base of the skull was by plain radiography. Because of the low sensitivity of these investigations, traditional teaching has included the sphenoid sinus in the volume of irradiation. Increase in longevity of patients allows the manifestation and documentation of the long-term sequelae of irradiating the hypothalamic-pituitary axis and the temporal lobes. This study is an attempt to evaluate whether the hypothalamic-pituitary axis can be shielded from the target volume in a proportion of NPC patients.

One hundred fifty-two NPC patients with no evidence of erosion of the base of the skull and sphenoid, nor extension to the nasal fossa and ethmoid sinuses were randomized to receive standard radiotherapy covering the whole sphenoid sinus or radiotherapy using a modified technique that shields the pituitary and the anterior part of the hypothalamus. This modified technique also shields a large part of the lower temporal lobes that are otherwise covered by standard treatment portals. The characteristics and treatment of the two subgroups of patients were otherwise comparable.

At a median follow-up of 31.5 months, the tumor control between the two subgroups of patients were comparable (p = 0.3928). However, 8 of the 71 patients in the unshielded group had developed symptomatic neuroendocrine complications, while none of the other group did (p = 0.0061). Two patients developed secondary hypothyroidism, one patient developed oligomenorrhoea associated with raised prolactin, and five patients developed temporal lobe necrosis.

The protective effect on neuroendocrine complication of this shield was demonstrated at median follow-up of 31.5 months, and the local control was not jeopardized. Modification of treatment technique as presently described, which is applicable to one-third of NPC patients to improve the therapeutic ratio, is recommended for general use.