Purpose: To study the efficacy of intracavitary brachytherapy (ICT) in early T-stage nasopharyngeal carcinoma (NPC).
Methods and materials: All early T-stage (T1 and T2 nasal cavity tumour) NPC treated with a curative intent up to 1996 were analyzed (n=743), 163 from the Prince of Wales Hospital (PWH) and 25 from Tuen Mun Hospital (TMH) were given ICT after radical external radiotherapy (ERT; group A). They were compared with 555 patients treated with ERT alone (group B). The radiotherapy techniques were identical between the two hospitals. The ERT delivered the tumoricidal dose (uncorrected biological equivalent dose (BED)-10, > or = 75 Gy) to the primary tumour, and this did not differ in technique or dosage between the two groups. The ICT delivered a dose of 18-24 Gy in three fractions over 15 days to a point 1 cm perpendicular to the midpoint of the plane of the sources.
Results: The local failure was significantly less (crude rates, 6.9 vs. 13.0%; 5-year actuarial rates, 5.8 vs. 11.7%) and the disease-specific mortality was significantly lower (crude rates, 13.8 vs. 18.9%; 5-year actuarial rates, 12.2 vs. 15.2%) in group A compared with group B. ICT was the only significant independent prognostic factor predictive of fewer local failures. When ICT was excluded from the Cox regression model, the total physical dose or the total BED-10 uncorrected for tumour repopulation became significant in predicting the ultimate local failure rate. The two groups were comparable in the rate of the chronic radiation complications. A significant dose-tumour-control relationship existed, plotting the local failure as a function of the total physical dose or the total BED.
Conclusions: Supplementing ERT, which delivered the tumoricidal dose (uncorrected BED-10, > or = 75 Gy), with ICT significantly enhanced ultimate local control in early T-stage (T1/T2 nasal infiltration) NPC. A significant dose-tumour-control relationship exists above the conventional tumoricidal dose level.