Parametric contrast-enhanced ultrasound as an early predictor of radiation-based therapeutic response for lymph node metastases of nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC) is a common type of cancer in South East Asia with peculiar epidemiology, pathology, clinical behavior and response to treatment characteristics. To the best of our knowledge, this is the first study to investigate the use of a contrast-enhanced ultrasound (CEUS) as a predictor for the therapeutic response in lymph node metastases of NPC patients treated with radiation-based therapy. Sixty-seven NPC patients with lymph node metastases underwent the lymph nodes CEUS examination twice; pre- and in-treatment (at the 5th fraction radiotherapy), respectively. The CEUS parameters were acquired through Qontrast_4.0 software and mainly included peak intensity (PI) and time to peak (TTP). The response assessment at the lymph nodes revealed a complete response (CR) in 48 patients and partial response (PR) in 19 patients. There was a significant difference in pre-treatment PI (PIpre) between the patients who showed CR or PR, but the predicted sensitivity and specificity of PIpre was low. The mean in-treatment PI (PIin) value of the lymph nodes that achieved a CR was 34.24±3.78%, which was significantly higher than the PIin value for PR, 25.62±2.30% (P<0.001). Furthermore, the PIratio, a PI-quotient, was calculated by dividing the PIin by the corresponding PIpre. The higher PIratio was also observed in CR lymph nodes (0.81±0.01 vs. 0.66±0.01; P=0.001), and the mean change in PI (PIΔ; PIΔ = PIpre-PIin) was smaller in the patients with CR nodes compared to the patients with PR nodes (7.79±3.28 vs. 13.77±1.90%; P=0.000). No difference was observed in TTPpre or TTPin between the CR or PR lymph nodes patients. A receiver operating characteristic curve was constructed to assess the accuracy of the parameters for the prediction of the therapeutic responses. The sensitivity and specificity of PIin in predicting the therapeutic response was 94.3 and 88.2%, and the corresponding figures of the PIratio were 92.5 and 83.8%, respectively. The CEUS parameters during the early course of radiation-based therapy, PIin and PIratio, are associated with the therapeutic response of NPC lymph node metastases, with a high predicted sensitivity and specificity, thus yielding the conceivable predictors with the potential to individualize treatment.