Adaptive radiotherapy for virally mediated head and neck cancer

Introduction: Clinical investigation has revealed a subgroup of head and neck cancers that are virally mediated. The relationship between nasopharyngeal cancer and Epstein Barr Virus (EBV) has long been established and more recently, the association between oropharyngeal cancer and Human Papillomavirus (HPV) has been revealed1,2 These cancers often present with nodal involvement and generally respond well to radiation treatment, evidenced by tumour regression1. This results in the need for treatment plan adaptation or re-planning in a subset of patients. Adaptive techniques allow the target region of the radiotherapy treatment plan to be altered in accordance with treatment-induced changes to ensure that under or over dosing does not occur3. It also assists in limiting potential overdosing of surrounding critical normal tissues4. We sought to identify a high-risk group based on nodal size to be evaluated in a future prospective adaptive radiotherapy trial. Method: Between 2005-2010, 121 patients with virally mediated, node positive nasopharyngeal (EBV positive) or oropharyngeal (HPV positive) cancers, receiving curative intent radiotherapy treatment were reviewed. Patients were analysed based on maximum size of the dominant node at diagnosis with a view to grouping them in varying risk categories to determine the need of re-planning. The frequency and timing of the re-planning scans were also evaluated. Results: Sixteen nasopharyngeal and 105 oropharyngeal tumours were reviewed. Twenty-five (21%) patients underwent a re-planning CT at a median of 22 (range, 0-29) fractions with 1 patient requiring re-planning prior to the commencement of treatment. Based on the analysis, patients were subsequently placed into risk categories; ≤35mm (Group 1), 36-45mm (Group 2), ≥46mm (Group 3). Re-planning CT’s were performed in Group 1- 8/68 (11.8%), Group 2- 4/28 (14.3%), Group 3- 13/25 (52%). Conclusion: In this series, patients with virally mediated head and neck cancer and nodal size > 46mm appear to be a high-risk group for the need of re-planning during a course of curative radiotherapy. This finding will now be tested in a prospective adaptive radiotherapy study. ‘Real World’ Implications: This research identifies predictive factors for those patients with virally mediated head and neck cancer that will benefit most from treatment adaptation. This will assist in minimising the side effects experienced by these patients thereby improving their quality of life after treatment.