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Background: Previous researches have demonstrated that adaptive replanning during intensity-modulated radiation therapy (IMRT) could enhance the prognosis of patients with nasopharyngeal carcinoma (NPC). However, the delineation of replanning target volumes remains unclear. This study aimed to evaluate the feasibility of reducing target volumes through adaptive replanning during IMRT by analyzing long-term survival outcomes and failure patterns of locoregional recurrence in NPC. Methods: This study enrolled consecutive NPC patients who received IMRT at our hospital between August 2011 and April 2018. Patients with initially diagnosed, histologically verified, non-metastatic nasopharyngeal cancer were eligible for participation in this study. The location and extent of locoregional recurrences were transferred to pretreatment planning computed tomography for dosimetry analysis. Results: Among 274 patients, 100 (36.5%) received IMRT without replanning and 174 (63.5%) received IMRT with replanning. Five-year rates of locoregional recurrence-free survival (LRFS) were 90.1% (95%CI, 84.8% to 95.4%) and 80.8% (95%CI, 72.0% to 89.6%) for patients with and without replanning, P = 0.045. There were 17 locoregional recurrences in 15 patients among patients with replanning, of which 1 (5.9%) was out-field and 16 (94.1%) were in-field. Among patients without replanning, 19 patients developed locoregional recurrences, of which 1 (5.3%) was out-field, 2 (10.5%) were marginal, and 16 (84.2%) were in-field. Conclusions: In-field failure inside the high dose area was the most common locoregional recurrent pattern for non-metastatic NPC. Adapting the target volumes and modifying the radiation dose prescribed to the area of tumor reduction during IMRT was feasible and would not cause additional recurrence in the shrunken area. [ABSTRACT FROM AUTHOR]

Background: Replanning in intensity-modulated radiotherapy (IMRT) has been reported to improve quality of life and loco-regional control in patients with nasopharyngeal cancer (NPC). Determination of the criteria for replanning is, however, urgently needed. We conducted a prospective study to determine when and for what type of patients is replanning preferred through weekly repeat computed tomography (CT) imaging during the course of IMRT.Methods: We recruited 20 patients who were diagnosed as having loco-regionally advanced, non-metastatic stage III or IVa NPC and treated with concurrent platinum-based chemoradiotherapy (CRT) using IMRT. Patients received CT simulation (sim-CT) and plain magnetic resonance imaging (MRI) plus diffusion-weighted imaging (DWI) weekly for five consecutive weeks. The gross tumor volume (GTV) and clinical target volume (CTV) were delineated and recorded weekly based on the CT-CT fusion. The relationship between GTV/CTV reduction and clinical characteristics of the patients were assessed using Pearson correlation test.Results: GTV and CTV decreased during the treatment by 36.03 mL (range, 10.91-98.82 mL) and 76.79 mL (range, 33.94-125.14 mL), respectively, after 25 fractions of treatment. The percentage reductions from their initial volume were 38.4% (range, 25.3-50.7%) and 11.8% (range, 6.7-18.3%), respectively. The greatest reductions in GTV and CTV were observed at the fourth week (i.e., upon completion of 20 fractions), compared to pre-treatment sim-CT. Weight loss and CTV reduction were significantly correlated with pre-treatment body mass index (BMI ) (r =0.58, P =0.012, and r =0.48, P =0.046, respectively). However, no significant correlation was observed between CTV reduction and initial tumor volume. In addition, GTV reduction was not significantly correlated with pre-treatment tumor volume (P =0.65), but negatively correlated with pre-treatment tumor apparent diffusion coefficient (ADC) values (r = -0.46, P =0.042).Conclusions: Our results indicate that the most appropriate replanning time is after 20 fractions of treatment, and pre-treatment BMI and ADC are potential predictive factors for the determination of replanning during IMRT. [ABSTRACT FROM AUTHOR]