Induction chemotherapy reduces target volume drift in patients with locoregionally advanced nasopharyngeal carcinoma undergoing adaptive intensity-modulated radiotherapy: a retrospective cohort study

Background: Adaptive radiotherapy (ART) provides real-time correction of the target and dose of radiation based on repeat computed tomography (CT) imaging and replanning during intensity-modulated radiation therapy (IMRT) and is important for locoregionally advanced nasopharyngeal carcinoma (NPC). However, repeat CT imaging and replanning are time-consuming and hinder the broader application of ART. The optimum dose and frequency of replanning time have been published in previous reports. The purpose of this study was to determine whether induction chemotherapy (IC) reduces target volume drift during IMRT, potentially reducing the replanning workload. Methods: From January 2012 to December 2017, 40 patients with locoregionally advanced, nonmetastatic stage III-IVa NPC treated in the Department of Radiation Oncology in the First Affiliated Hospital, College of Medicine, Zhejiang University, were enrolled into this study. Of the 40 patients, 20 received 2-3 cycles of IC before concurrent chemoradiotherapy (IC + CCRT), and the other 20 patients were treated with CCRT plus adjuvant chemotherapy (CCRT + AC). During CCRT, all patients underwent weekly simulated CT for 6 weeks. The gross tumor volume (GTV), clinical target volume (CTV), and body weight were measured weekly and compared between the 2 groups. Results: Compared with the baseline, the mean weight loss after 25 fractions was 7.0 kg (13.6%; range, 3.9-25.5%) in the CCRT + AC group and 5.7 kg (8.3%; range, 3.6-20%) in the IC + CCRT group. The mean GTV and CTV decreased by 16.55 mL (15.7%; range, 6.1-33.7%) and 61.25 mL (9.33%; range, 4.4-17.0%), respectively, in the IC + CCRT group, and by 39.86 mL (38.79%; range, 25.3-50.7%) and 87.72 mL (12.7%; range, 6.7-22.9%), respectively, in the CCRT + AC group. The degree of weekly reduction in the GTV of the IC + CCRT group was not significantly higher than that of the CCRT + AC group, with the following P values of each percentage reduction in comparison with the previous week over 5 weeks, respectively: P<0.001, P=0.015, P=0.01, P=0.01, and P<0.001. The weekly CTV reduction only significantly correlated with weight loss (P=0.005) in the IC + CCRT group. Conclusions: IC significantly decreased the degree of weight loss, GTV shrinkage, and CTV reduction during CCRT, consequently decreasing the anatomical and target dose drift during the adaptive replanning of IMRT. This may lead to a reduction in the recurrence of locoregionally advanced NPC, especially among patients with large metastatic cervical lymph nodes, potentially improving survival. This result provides favorable evidence that IC improves locoregional recurrence-free survival (LRFS) and overall survival (OS) in patients with locoregionally advanced NPC.