Prospective Study of PET/MRI Tumor Response During Chemoradiotherapy for Patients with Low and Intermediate Risk p16-positive Oropharynx Cancers

Abstract

<h3>Purpose/Objective(s)</h3> To compare the intratreatment PET/MRI tumor response in patients with low-risk (LR) and intermediate-risk (IR) p16-positive oropharynx cancer during chemoradiotherapy. <h3>Materials/Methods</h3> Patients with non-metastatic, p16-positive oropharynx cancer were treated with definitive chemoradiotherapy. LR disease was defined as cT0-3 and cN0-2b and </= 10 pack-years and IR disease as cT4 or cN2b-3 or > 10 pack-years. Patients underwent a PET/MRI scan pre-treatment and at fraction 10. PET/MRI data used for analysis of the primary tumor and largest node included changes in volume, SUVmax, SUVmedian, SUVpeak, and diffusion. Radiographic differences between LR and IR patients were compared using the standard t-test. Principal component analysis, with K-means and Euclidean distance functions were used for patient clustering. Silhouette width was used to determine the optimal number of clusters similarity of objects within each cluster. Linear regression was performed on all radiographic metrics using patient and disease characteristics. <h3>Results</h3> Twenty-four patients were enrolled with 7 LR and 11 IR patients available for analysis. Cluster analysis defined two cohorts that exhibited a similar intratreatment response. Cohort 1 contained 7 of 7 LR patients and 8 of 11 IR patients. Cohort 2 contained 3 of 11 IR patients. There was a trend for patients in Cohort 2 to be older (mean 68 years ± 5 versus 59 years ± 7; p = 0.057) and have a higher smoking history (mean 30 pack-years ± 40 s.d. versus 12 pack-years ± 17 s.d.; p = 0.2). Cluster 2 exhibited significant differences compared to cluster 1 in the change in primary tumor SUVpeak (0.46 mean ± 0.15 s.d. versus -0.22 mean ± 0.24 s.d.; p < 0.001) and largest lymph node SUVmedian (0.43 mean ± 0. s.d. versus -0.00 mean ± 0.9 s.d.; p = 0.001) after 10 fractions of chemoradiotherapy. <h3>Conclusion</h3> We demonstrate that intermediate-risk p16-positive oropharynx cancers exhibit heterogeneity in their radiographic response to chemoradiotherapy. These data support further study of intratreatment image response as a mechanism for identifying patients with intermediate-risk disease suitable for therapy de-intensification.