[Prophylactic irradiation at the level Ib for nasopharyngeal carcinoma: should that be a routine?]

To assess the necessity of routine prophylactic irradiation at the level Ib for nasopharyngeal carcinoma (NPC).

Newly diagnosed NPC patients between January, 2001 and June, 2005 were enrolled in this study. The nodal distribution in each region was calculated from the data of transversal contrast enhance CT or magnetic resonance scan of the head and neck.

Cervical node involvement was found in 75.1% of the 338 patients enrolled. The rates of involvement at levels Ib, IIa, IIb, III, IV, Va, Vb and in the supra-clavicular region were 0.9%, 49.1%, 60.7%, 26.0%, 5.9%, 9.5%, 3.8% and 0.9%, respectively. Skip metastasis occurred only in 2.4% of the cases. The high risk region (defined by a probable risk>5%) of nodal metastases was (1) the ipsilateral levels III, IV, Va, and Vb in case of level II involvement, (2) the ipsilateral levels II, IV, Va, and Vb in case of level III involvement, (3) the ipsilateral levels II, III, Va, Vb and the supra-clavicular region in case of level IV involvement, (4) the ipsilateral levels II, III, IV, Vb and the supra-clavicular region in case of level Va involvement, (5) the ipsilateral levels II, III, IV, Vb, and the supra-clavicular region in case of level Vb involvement, (6) the contralateral levels II, III, and Va in case of unilateral cervical node involvement.

Nodal involvement in NPC patients rarely occurs at the level Ib, which is not a high risk region whatever the regions may be to have lymph node metastasis and therefore does not need routine prophylactic irradiation.