The strategy and feasibility of dose optimization in clinical target volume Ⅱb in patients with N 0-N 1 nasopharyngeal carcinoma / 中华放射肿瘤学杂志

ABSTRACT

Objective:To determine the safety of prophylactic irradiation dose CTV 60Gy optimized to CTV 50Gy for II b region in patients with stage N 0-N 1 nasopharyngeal carcinoma (NPC) and the dose advantage and clinical value for parotid gland protection, and to understand the diagnostic value of PET-CT and diffusion-weighted imaging (DWI) for suspicious positive lymph nodes in the neck (5 mm≤maximum short diameter<10 mm). Methods:Clinical data of 157 patients with primary non-metastatic NPC (N 0-N 1) admitted to our hospital from June 2015 to March 2017 were retrospectively analyzed. 104 patients underwent II b clinical target volume optimization guided by multimodal imaging system. Survival analysis was performed by Kaplan - Meier method. Univariate/multivariate regression analysis was performed to analyze the pattern of cervical lymph node recurrence. Paired t-test was used to compare the differences in target volume and parotid gland dose parameters before and after dose optimization. Results:Sixty patients underwent single-neck optimization in stage N 1, 25 patients received double-neck optimization (only those with retropharyngeal lymph node metastasis), and 19 patients underwent double-neck optimization in stage N 0. Three patients had cervical regional recurrence, all in-field. The 5-year overall survival rate was 93.3%. The lymph node recurrence-free survival rate, local recurrence-free survival rate, distant metastasis-free survival rate and disease-free survival rate were 97.1%, 91.3%, 88.5% and 80.8%, respectively. Cervical lymph node recurrence was associated with local recurrence in the nasopharynx, regardless of retropharyngeal lymph node status. Fourteen patients had suspicious positive cervical lymph nodes in II b region, with a mean maximum short diameter of 7.1 (5~9) mm on the largest cross-sectional plane, and 11 of them were positive on PET-CT, with a mean SUV max of 2.96 (2.5~3.3). There was no significant difference in GTV after optimization ( P>0.05). D mean, D max, D 50% and V 26Gy of parotid gland were significantly lower than those of conventional plan (all P<0.01). Conclusions:It is safe to optimize CTV 60Gy to CTV 50Gy in II b region in patients with N 0-N 1 NPC, and the exposure dose to normal tissues around the parotid gland and neck is significantly reduced. For small lymph nodes that do not meet the diagnostic criteria, it needs to be individualized in combination with multimodality imaging systems, such as PET-CT and DWI.