Developing an Adaptive Radiotherapy Technique for Virally Mediated Head and Neck Cancer

Virally mediated head and neck cancers (VMHNC) often present with nodal involvement and are highly radio responsive, meaning that treatment plan adaptation during radiotherapy (RT) in a subset of patients is required. This study sought to determine potential risk profiles and a corresponding adaptive treatment strategy for these patients.

One hundred twenty-one patients with virally mediated, node positive nasopharyngeal (Epstein-Barr virus positive) or oropharyngeal (human papillomavirus positive) cancers who were receiving curative intent RT were reviewed. The type, frequency, and timing of adaptive interventions, including source-to-skin distance (SSD) corrections, rescanning, and replanning, were evaluated. Patients were reviewed based on the maximum size of the dominant node to assess the need for plan adaptation.

Forty-six patients (38%) required plan adaptation during treatment. The median fraction at which the adaptive intervention occurred was 26 for SSD corrections and 22 for replanning CTs. A trend toward three risk profile groupings was discovered: (1) low risk with minimal need (<10%) for adaptive intervention (dominant pretreatment nodal size of ≤35 mm), (2) intermediate risk with possible need (<20%) for adaptive intervention (dominant pretreatment nodal size of 36-45 mm), and (3) high risk with increased likelihood (>50%) for adaptive intervention (dominant pretreatment nodal size of ≥46 mm).

In this study, patients with VMHNC and a maximum dominant nodal size of >46 mm were identified at a higher risk of requiring replanning during a course of definitive RT. Findings will be tested in a future prospective adaptive RT study.