2271 - Role of Diffusion Weighted Imaging in Prediction of Patterns of Failure for Recurrent Head and Neck Cancer

D. H. El-Habashy¹, J. Khriguian², S. Attia¹, Y. Khamis³, M. R. Abdelaal¹, M. Naser¹, C. D. Fuller¹, and A. S. Mohamed¹; ¹Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ²The university of Texas MD Anderson Cancer Center, Houston, TX, ³MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s): The identification of the biologically radioresistant subvolumes within the primary tumor volumes is an essential step towards biologically guided radiation therapy (RT) dose painting application. Therefore, the aim of our study is to assess the radioresistant subvolumes using quantitative MRI-guided characterization of the patterns of failure in head and neck cancer patients Materials/

Methods: Forty patients with head and neck cancer who have developed local and/ or regional recurrence were included. The recurrence diagnostic CT (rCT) was co-registered with the planning CT (pCT) using a validated deformable image registration software (Velocity AI). Subsequently, pCTs were co-registered with baseline DWI. The manually segmented recurrent gross disease (rGTV) was then propagated to the co-registered pCTs and baseline DWI. For the pCTs, the mapped rGTVs were assessed dosimetrically concerning the planned dose and spatially in relation to planning target volumes. Failures were classified based on combined spatial/dosimetric criteria into categories A (central high-dose), B (peripheral high-dose), C (central intermediate/low-dose), D (peripheral intermediate/low-dose), and E (extraneous-dose). The center of mass of the rGTV_DWI was generated as a surrogate of tumor recurrence origin and aparant diffusion coefficient (ADC) values were extracted for both the centroid and the whole rGTV volumes and compared to the baseline GTV.
Results: The mean age of the patients included in the study was 60.3 years, with the oropharynx being the most common site for the primary tumor. Approximately one-third of the patients (n=14, 35%) were diagnosed with stage IVa disease at the time of initial diagnosis. Type A failure was the most prevalent (n=30, 71.4%). The mean ADC values for baseline GTV, rGTV, and centroid volume were 1.27, 1.35, and 1.23, respectively. For type A failure, the mean ADC values for baseline GTV, rGTV, and centroid volume were 1.30, 1.40, and 1.24, respectively. For type B failure, the mean ADC values for baseline GTV, rGTV, and centroid volume were 0.94, 1.40, and 1.40, respectively. For type C failure, the mean ADC values for baseline GTV, rGTV, and centroid volume were 1.00, 0.85, and 0.82, respectively. For type D failure, the mean ADC values for baseline GTV, rGTV, and centroid volume were 1.30, 1.60, and 1.70, respectively. For type E failure, the mean ADC values for baseline GTV, rGTV, and centroid volume were 1.36, 1.26, and 1.12, respectively.
Conclusion: The most frequent type of failure observed was central local failure. There were no significant differences detected between baseline ADC values and the baseline GTV, rGTV, or centroid volume. Similarly, no significant correlations were found between baseline ADC values and the different types of failures. Further studies with larger cohorts and multi-institutional data are needed for validation of ADC as a model for prediction of type of failure after definitive RT in head and neck cancer patients