Early Response Assessment on Mid-Treatment CT Predicts Loco-Regional Recurrence in Oropharyngeal Cancer Patients Treated with Definitive Radiation Therapy

Publication date: Available online 6 April 2018
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Rafi Kabarriti, N. Patrik Brodin, George Lundgren, Nitin Ohri, Wolfgang A. Tomé, Shalom Kalnicki, Madhur K. Garg
Purpose/Objective(s)To evaluate if response assessment based on mid-treatment computed tomography (CT) scans during definitive radiation therapy (RT) for oropharyngeal head and neck cancer (HNC) can predict for loco-regional recurrence (LRR).Materials/MethodsHNC patients treated at our institution with RT undergo CT rescans at 15^th fraction and are replanned in case of inadequate dose to gross disease or increased dose to organs-at-risk. A retrospective cohort analysis was performed on 96 consecutive patients with oropharyngeal cancer treated in 2007-2015 with mid-treatment rescans. The volume of primary disease and involved lymph nodes were delineated on pre- and mid-treatment CT. Univariable and multivariable Cox proportional hazards regression analysis were used to evaluate the efficacy of mid-treatment reduction in tumor volume as a predictor of LRR. Risk-stratification was performed by dichotomizing patients into high- and low-risk groups based on mid-treatment response as well as p-16 status and smoking history.ResultsWith a median follow-up of 34 months, 14 patients experienced LRR. The median reduction in total tumor volume was 18.7% (IQR: 8.4%-30.9%). Reduction in total tumor volume > median is an independent predictor of LRR (HR: 0.22; 95%CI: 0.05–0.89; p=0.020), and the reduction in primary tumor volume is an even stronger predictor (HR: 0.11; 95%CI: 0.02–0.57; p=0.002). Stratifying patients into a high-risk group with reduction in total tumor volume at mid-treatment ≤ median, p-16 negative status, and smoking status >10 pack years, and a low-risk group without these factors, there was a clear separation in Kaplan-Meier curves with actuarial 3-year loco-regional control, progression-free survival and overall survival rates for the high-risk patients of 45.7%, 38.2%, 71.8% compared to 90.7%, 70.6%, 89.8% for low-risk patients, respectively (p≤0.021 for all).ConclusionOur study shows that early response assessment based on mid-treatment CT is an independent predictor of LRR and can be used to effectively distinguish high-risk and low-risk patients, allowing for risk-adaptive treatment stratification at the midway point.

Teaser

In a cohort study of 96 oropharyngeal cancer patients undergoing definitive radiation therapy, we identified early response assessment based on mid-treatment CT at the 15^th RT fraction as an independent predictor of locoregional recurrence. Combining this with p-16 and smoking status, we were able to effectively distinguish high-risk and low-risk patients, potentially allowing for more precise risk-adaptive treatment stratification.


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