Computed tomography findings of bony regeneration after radiotherapy for nasopharyngeal carcinoma with skull base destruction: implications for local control

PURPOSE: To evaluate the response of bony destruction (BD) of the skull base following radiotherapy in nasopharyngeal carcinoma (NPC) and investigate the implications of bony regeneration (BR) on local control and its related factors. METHODS AND MATERIALS: Ninety patients with NPC with skull base destruction clearly demonstrated on computed tomography (CT) were reviewed. These patients have completed the prescribed treatment and received regular CT follow-up. A total of 338 sets of CT images of the head and neck were reviewed. The tumor response and the appearance of BR in the previous destructive part of the skull base were recorded and analyzed. The tumor response was divided into complete, partial, or no response. BR was defined as recalcification or sclerotic change with partial or complete healing in the previous osteolytic bony defect. Local failure was confirmed either by pathological or merely by imaging studies showing progression of tumor in consecutive radiological pictures. RESULTS: The distribution of specific sites of bony destruction (BD) in these patients included the sphenoid bone (68%), paracavernous sinus area (48%), petrous apex (47%), clivus (44%), pterygoid plates (20%), and others (7%). The CT showed 57 patients (63%) had BR. All were observed within 1 year after treatment. Sixty-two patients (69%) had complete tumor response after treatment. Analyzed by logistic regression method, tumor response after treatment was found to have a statistically significant correlation with BR (p = 0.0004). Most BR (55/57) was demonstrated in patients with complete tumor response. The 3-year actuarial local control rate was 54 % in these patients. The local control was quite different in the comparison of patients with BR versus those with persistent BD (77% vs. 21%, p < 0.0001). Multivariate analysis showed that patients with complete tumor response or with BR on imaging had statistically better local control than those without either of the two findings (p < 0.05). CONCLUSION: Appearance of BR at previous destructive skull base following radiotherapy for NPC patients could be clearly demonstrated on CT. Bony regeneration significantly correlated with treatment response and local control. Although the underlying significance of BR was unknown, to predict the outcome after treatment, the appearance of BR shown on CT may imply the complete eradication of tumor in this area.