Phase II Study Investigates the Potential of ADC as a Predictive MRI Biomarker for Radiation Treatment Efficacy for Nasopharyngeal Concurrent Chemo/RT

Presenting author:
Mei Feng, MD, PhD

By Brian Winey, PhD, Massachusetts General Hospital,
Harvard Medical School

Biomarkers for radiation therapy (RT) are critical for the evaluation of outcomes, complications, response and efficacy. Multiple studies have demonstrated that MRI can detect biological changes in the tumor or surrounding tissues during and following radiation therapy. The Apparent Diffusion Coefficient (ADC) is one MRI based biomarker potentially useful for the evaluation of treatment efficacy in head and neck patients. Prior studies have demonstrated the feasibility and challenges of using ADC as a biomarker for head and neck radiation therapy assessment, including a single pre-RT time point.

Simultaneous with studies demonstrating the potential utility of MRI biomarkers, MR-guided RT is becoming more available as an integrated imaging and treatment modality, giving rise to the opportunity of MRI biomarker assessment immediately prior to or during treatment delivery. While MR- guided RT can provide unparalleled visualization of many soft tissue treatment targets, the potential of using the MR-linac for assessment of biomarkers is an additional potential benefit of MR-guided RT.

The abstract Early Efficacy Prediction of Nasopharyngeal Carcinoma Based on 3-D-ADC Acquired During Radiotherapy: A Phase II Prospective Study by Mei Feng, MD, PhD, et al. is a prospective study investigating the potential of ADC as a predictive MRI biomarker for radiation treatment efficacy for nasopharyngeal concurrent chemo/RT (CCRT). While the current study did not use an integrated MR-linac system, the study does analyze the potential of ADC MRI biomarker during radiation therapy.

The current study of 50 squamous NPC patients treated with CCRT (total dose of 66-70 Gy in 33 fractions) utilized an offline 3.0 T MRI acquisition of diffusion weighted (DWI) at four time points: pre-RT, 5th fraction, 15th fraction and post-RT. The mean ADC values of the gross tumor volume and lymph node contours were calculated at each time point, and the tumor response was evaluated with the RECIST 1.1 criteria. Similar to another report published at the end of 2020, Dr. Feng et al. demonstrate that the mean ADC values significantly increase during treatment at both time points, the 5th and 15th fractions, compared to the pre-RT ADC values. Additionally, the current abstract added the tumor response assessment with the RECIST 1.1 criteria and determined that the change in ADC value between the pre-RT and 5th fraction was most significantly correlated with the tumor response, assessed to be 58% CR and 42% PR. Importantly, the study demonstrated that the volume and absolute values of the ADC were not correlated with the tumor response.

Given the increased number of MR-linac treatment systems and the increased opportunities for treatment assessment using MRI biomarkers, Dr Feng et al. demonstrate that the early change in the mean ADC values might serve as an early treatment assessment tool and predictor for treatment efficacy for head and neck patients. Given the utility of early ADC changes prior to a measurable (RECIST 1.1 criteria) tumor response, the biomarker could be used as a threshold or trigger for treatment adaptation. More work is needed to determine how the current treatment paradigms can be adjusted based upon biomarker information. In addition to a parallel study they published looking at parotid toxicity, Dr. Feng et al. also plan to extend the current study to evaluate more long-term patient outcomes and consider if the immediate tumor response is predictive of long-term patient outcomes and survival rates.

Abstract 39 - Early Efficacy Prediction of Nasopharyngeal Carcinoma Based on 3-D-ADC Acquired During Radiotherapy: A Phase II Prospective Study was presented on October 25, 2021, during the SS 06 session – Best of Physics.

Published October 26, 2021

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