Early efficacy prediction of nasopharyngeal carcinoma based on 3D-ADC value acquired during radiotherapy: A phase II prospective study.

Abstract

e18018 Background: Concurrent chemoradiotherapy (CCRT) is the main treatment for locally advanced nasopharyngeal carcinoma (LANPC). The prognosis of the patients with the same stage receiving the same treatment varies greatly. We aimed to investigate the dynamic changes of apparent diffusion coefficient (ADC) map from diffusion weighted MRI (DWI) of primary tumor (PT) and metastatic lymph nodes (LN) for NPC patients during RT process, and analyzed the potential correlations with volume reduction and objective response rate (ORR). Methods: A total of 50 NPC patients treated with CCRT were enrolled in this prospective study. All patients received a planned total dose of 66 to 70Gy in 33 fractions at 5 fractions per week using Image-guided intensity modulated radiotherapy (IGRT). The CCRT protocol was cisplatin (80-100mg/m2) every 3 weeks for 3 cycles. All patients received DWI scan at pre-RT, the 5th and 15th fractions and immediately post-RT on a 3.0T MRI system (b=0, 500, 800s/mm2) system. The ADC values of PT and LN were acquired on ADC map. RECIST1.1criteria was used to evaluate the ORR for both PT and LN. Clinical predictors of complete response (CR) were evaluated using log-rank test. Multivariate analyses were calculated using the logistic regression model. Receiver-operating characteristic (ROC) curve was used to determine the cut-off value of ADC value. P <0.05. Results: After the completion of C CRT, the ORR of the PT was 100% (CR 75%, PR 25%), and that of the LN also reached 100% (CR 52%, PR 48%). Mean ADC increases and volume reductions in PT and LN were observed during RT. In the first stage (from pre-RT to the 5th fraction), the mean ADC increased significantly by 20.78% (PT), 22.96% (LN), while the volumes of PT and LN had minimal changes (PT:18.42cm3vs 16.72cm3, LN: 4.67cm3 vs 4.12cm3). In the second stage (from the 5th fraction to post-RT), the mean ADC increased by 45.58% (PT), 41.2% (LN), the volumes decreased by 86.07% (PT), 61.6% (LN). The increased mean ADC at the first stage had a positive correlation with the volume reduction after RT (r PT=0.32; r LN=0.40). Univariate analysis showed significant differences in the age, the changes of 3D-ADC at the 5th RT and the volume of PT and LN before RT (VPT, VLN) between CR group and PR group(p<0.05), The binary logistic regression analysis demonstrated the ADC changes and the VPT, VLN were predictor of PT and LN efficacy evaluation. ROC analysis suggested the ADC changes had the better performance for PT and LN efficacy evaluation. The cut-off the ADC value changes of PT and LN was 193.52mm2/s (AUC = 0.750, p = 0.008) , 173.80mm2/s (AUC = 0.822, p < 0.001) respectively. Conclusions: 3D-ADC values of PT and LN increased dramatically during RT for NPC patients. The 3D-ADC value of PT and LN was an independent prognostic factor for NPC patients. Early ADC changes at the 5th fraction might be a new and sensitive biomarker to predict the efficacy for NPC patients.