Reduction of Target Volume and the Corresponding Dose for the Tumor Regression Field after Induction Chemotherapy in Locoregionally Advanced Nasopharyngeal Carcinoma.

Purpose: This study aims to investigate the feasibility of contouring target volume according to residual tumor and decreasing the dose to the tumor regression field after induction chemotherapy (IC) in locoregionally advanced nasopharyngeal carcinoma (NPC).

Materials and Methods: From August 2009 to August 2013, patients with stage III-IVB NPC were treated with IC and concurrent chemoradiotherapy. GTVnx-residual and GTVnd-residual were contoured according to post-IC residual primary tumor and any N+ disease, respectively. The tumor regression field was included in CTVnx1 /CTVnd1 and prescribed a dose of 60 Gy. Outcomes and toxicities of all patients were evaluated.

Results: A total of 57 patients were enrolled. At a median follow-up of 68 months, 3 cases displayed locoregional recurrence and 1 case showed both distant metastasis and locoregional recurrence. All locoregional recurrences were in the GTVnx-residual/GTVnd-residual and in-field. The five-year overall, locoregional relapse-free, distant metastasis-free, and progression-free survival rates were 82.2%, 85.8%, 87.7% and 80.3%, respectively.

Conclusion: After IC, contouring of GTVnx-residual/GTVnd-residual as residual tumor volume and distribution 60 Gy of radiation dose to the tumor regression field may be feasible and need further investigation.