873P - Early efficacy prediction of nasopharyngeal carcinoma based on 3D-ADC acquired during radiotherapy: A phase II prospective study

Background

Concurrent chemoradiotherapy (CCRT) is the main treatment model for locally advanced nasopharyngeal carcinoma. Previous study found the apparent diffusion coefficient (ADC) value of primary tumor partly correlated to prognosis for NPC patients. We aimed to observe the dynamic changes of ADC of gross target volume (GTV) and metastatic lymph nodes (LN) for NPC patients during radiotherapy (RT), and explored the potential correlations between ADC changes and treatment response.

Methods

50 squamous NPC (II-IVa) patients treated with definitive RT were enrolled in this study. The patients received DWI scan at pre-RT, the 5^th and 15^th fractions and immediately post-RT on a 3.0T MRI system. The ADC values of GTV and LN were acquired using MIM software. RECIST1.1 criteria were used to evaluate the tumor response. Multivariate analyses were calculated using the logistic regression model. Receiver-operating characteristic (ROC) curve was used to determine the cut-off value of ADC.

Results

After the completion of CCRT, the ORR for all the patients was 100% (CR 58%, PR 42%). The mean ADC value of GTV and LN gradually increased from pre-RT to post RT. These changes generally occurred in two stages. For the first stage (from pre-RT to the 5^th fraction), the mean ADC value of GTV and LN increased significantly by 20.78% and 22.96% respectively, while the volumes of GTV and LN had minimal changes (GTV:18.42cm³ vs 16.72cm³, LN: 4.67cm³ vs 4.12cm³). As for the second stage (from the 5^th fraction to post-RT), the mean ADC value of GTV and LN continued to increase by 45.58% and 41.2% respectively, while the volumes decreased by 86.07% (GTV) and 61.6% (LN). Multivariate analysis showed the mean ADC changes of GTV from pre-RT to the 5^th fraction (ΔADC5) was the only independent prognostic factor for treatment response of NPC. ROC showed that the cut-off value for ΔADC5 was 158.82mm²/s (sensitivity: 87%; specificity: 65%).

Conclusions

Mean ADC values of GTV and LN increased dramatically during RT for NPC patients. The mean ADC began to increase at the 5^th fraction, while the change of volume was minimal. Early ADC changes at the 5^th fraction might be a new and sensitive biomarker to predict the prognosis for NPC patients independently of volume change.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.