To investigate the initial irradiated dose of the recurrent site and local failures patterns after Intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC) patients with retropharyngeal lymph nodes (RLNs) metastasis only, with the aim to demonstrate the adequacy and overall quality of the target volume definitions for further improvement of outcome and therapeutic ratio.
382 newly diagnosed non-metastatic NPC patients were retrospectively enrolled, receiving elective neck irradiation to to levels II, III, VA. For patients with local failure, the location and extent of local failures were transferred to the pretreatment planning CT for dosimetric analysis. The dose of radiation received by GTVr (gross tumor volume of recurrence) was calculated and analyzed with dose-volume histogram (DVH). Failures were classified as: "in field" if 95% of GTVr was within the 95% isodose, "marginal" if 20% to 95% of GTVr was within the 95% isodose, or "outside" if less than 20% of GTVr was inside the 95% isodose.
With a median follow-up time of 61.3 months, 12 patients have developed local recurrence (10 cases available). The 5-year OS, LRFS, RRFS, DMFS and DFS were 87.8%, 95.2%, 99.1%, 93.3% and 82.5%, respectively. Dose conformity with IMRT was excellent and the recurrence was mainly within 3 years after the first treatment. The dosimetric analysis showed that 7 failures were classified as "in-field", 2 failures as "marginal" and only 1 failures as "out-field". Most local relapse site located just the same site of primary tumor and most anatomic sites were at low risk of concurrent bilateral tumor invasion.
IMRT with elective neck irradiation provides excellent local control for NPC patients without cervical lymph node metastasis. In-field failures are the main patterns for local recurrence and the radioresistant subvolumes within the GTV are needed to be identified. We proposed suggestions for reduction of target volume during IMRT treatment for NPC patients.
Clinical trial identification
Legal entity responsible for the study
Fudan University Shanghai Cancer Center.
Has not received any funding.
All authors have declared no conflicts of interest.