[Impact of changing gross tumor volume delineation of intensity-modulated radiotherapy on the dose distribution and clinical treatment outcome after induction chemotherapy for the primary locoregionally advanced nasopharyngeal carcinoma].

Background and objective: The gross tumor volume (GTV) obviously reduces after induction chemotherapy (IC) for primary locoregionally advanced nasopharyngeal carcinoma (NPC). This study was to investigate the impact of changing gross tumor volume delineation on the dose distribution and clinical treatment outcome after IC.

Methods: From January 2008 to April 2009, 24 patients with Stage III-IVb primary locoregionally advanced NPC were treated with TPF regimen IC followed by intensity-modulated radiotherapy (IMRT) with concurrent chemotherapy . The primary GTVs were delineated into two parts: the post-IC primary GTV (GTVpost-IC-NP), and the region of pre-IC primary GTV minus GTVpost-IC-NP (GTVpre-post-IC-NP). The dose distributions of two plans with GTVpost-IC-NP or pre-IC primary GTV were assessed by analyzing ten cases. The clinical treatment outcome and toxicity of all patients were observed.

Results: The post-IC GTV was significantly smaller than the pre-IC GTV (primary GTV 25.5 cm3 vs. 51.1 cm(3),P=0.001; lymph nodes GTV 9.1 cm(3) vs. 31.4 cm(3), P=0.035; primary + lymph nodes GTV 33.2 cm(3) vs. 82.6 cm(3),P=0.004), the overall GTV with an average shrinkage of 61%. The high dose region was also smaller after IC (volumes covered by 64.4 Gy were 422.9 cm3 vs. 457.9 cm3, P=0.003; 274.2 cm(3) vs.334.5 cm(3) by 68 Gy, P=0.041). The complete response rate was 38% after IC, and 100% three month after radiotherapy. The toxicity of following IMRT with concurrent chemotherapy was similar to that of IMRT with concurrent chemotherapy alone. With median follow-up of 9 months, the locoregionally control rate was 100% and only one patient presented metastasis 15 months after treatment.

Conclusions: TPF regimen IC could significantly reduce tumor volume. The following IMRT with GTVpost-IC-NP plan reduced the high dose region, which didn't add toxicity while had excellent short-term treatment outcome.