Local failure patterns for patients with nasopharyngeal carcinoma after intensity-modulated radiotherapy

Abstract

Background: To investigate the clinical feature and the local failure patterns after intensity-modulated radiotherapy for nasopharyngeal carcinoma.

Methods: Between March 2007 and July 2009, 710 patients with nasopharyngeal carcinoma were treated with intensity-modulated radiotherapy. The magnetic resonance imagings obtained at recurrence were registered with the original planning computed tomography for dosimetry analysis.

Results: With a median follow-up of 38 months, 34 patients have developed local recurrence (32 cases valid). The incidence of invasion to nasopharynx, parapharyngeal space and the retropharyngeal space by the primary tumors was 100%, 75.0% and 62.5%, respectively, but 78.1%, 34.4% and 21.9% at recurrence, respectively. The rate of invasion to ethmoid sinus was 3.1% by the primary tumors but 28.1% at recurrence (p=0.005). The topographic analysis of the local failure patterns showed "central" in 16 patients; "marginal" in 9; and "outside" in 7. The median volumes of primary gross tumor were 45.84 cm(3) in the central failure group, 29.44 cm(3) in the marginal failure group, and 21.52 cm(3) in the outside failure group, respectively (p=0.012), and the median volumes of primary clinical target1 were 87.28 cm(3), 61.90 cm(3) and 58.74 cm(3) in the three groups, respectively (p=0.033).

Conclusions: In patients with nasopharyngeal carcinoma treated with intensity-modulated radiotherapy, the recurrent tumors had their unique characteristic and regularity of invasion to adjacent structures. "Central" failure was the major local failure pattern. The volumes of primary gross tumor and clinical target1 were significantly correlated with recurrent patterns. Employ more aggressive approaches to tumor cells which will be insensitive to radiotherapy may be an effective way to reduce the central failure.

Figure 1

Delineation of target volumes. (a) The gross recurrent tumor volume (GTVr) was identified on MRI images. (b) The GTVr was transferred to the original planning CT. Red line is gross tumor volume (GTV); yellow line, CTV1; blue line, CTV2. (c) Cyan line, TG; orange line, TC1; green line, TC2; purple line, TE; TG+TC1+TC2+TE=GTVr.

Figure 2

Dose delivered to the recurrent site in primary treatment.

Figure 3

One patient with marginal failure. Part of primary tumor was just inside CTV2 (blue line), but outside GTV or CTV1. The white arrow indicates the recurrent tumor.