Head and neck adaptive radiotherapy: Predicting the time to replan

Aim: Head and neck (H&N) cancer patients can undergo anatomical change throughout radiotherapy treatment. Adaptive radiotherapy (ART) is effective in addressing the impact of this change on the planned dose distribution. The aim of this study was to identify pretreatment factors that influence the need for and timing of replanning for patients receiving chemoradiotherapy for node-positive nasopharyngeal (NPC) and oropharyngeal carcinoma (OPC). Methods: Of 110 patients enrolled in a prospective H&N ART study, 21 (19%) underwent a second planning scan (re-CT) and were included in this review. Univariate and multivariate analysis was used to compare those patients who were replanned with those that were not. Factors influencing the timing of replanning were assessed including patient and tumor characteristics and structure volume details. Results: Of the five replanned patients, three were diagnosed with NPC (P = 0.06) and had significantly larger initial nodal volumes (median volume 140.3 cc vs. 39.1 cc, P = 0.019). Overall the median time of re-CT was significantly different between replanned and non-replanned patients, with replanned patients having an earlier re-CT: median fraction 18 versus fraction 23 (P = 0.01). Specifically, NPC patients who were replanned had a re-CT performed earlier than OPC patients (median fraction 11 vs. 20). Conclusion: For H&N patients with large nodes receiving definitive chemoradiotherapy, replanning may be considered at the commencement of week 3 for NPC patients and in week 4 of treatment for OPC patients. This information may facilitate a forward planning approach to H&N ART that enables allocation of departmental resources prior to treatment commencement.