Feasibility and potential benefits of daily online adaptive radiotherapy for head and neck cancer without margin reduction using an RTT-only workflow

Introduction Online adaptive radiotherapy (oART) may improve head and neck cancer (HNC) treatment, where anatomical changes during radiotherapy (RT) are common. However, oART is resource-intensive and clinical data are limited. We conducted a prospective feasibility trial implementating an RT technologist (RTT)-led workflow to evaluate dosimetric outcomes, workflow strategies, and intrafractional motion in daily oART. Material and methods Ten patients receiving curatively intended oART (33–34 fractions) using standard PTV margins were included (NCT: 07506902). For each fraction, a scheduled plan (original plan recalculated on daily anatomy) and an adapted plan (reoptimized to daily anatomy) were generated, and the preferred plan was delivered. Target coverage (PTV1 V95%), mean dose (D mean ) and maximum dose (D max ) to selected organs at risk (OAR), treatment time, and baseline target volume were extracted for all fractions. The effect of oART (scheduled- versus delivered plan) was analyzed using linear mixed-effects models. Intrafractional motion was assessed weekly. Results A total of 322 adaptive session were completed. The median treatment time was 29.9 min. The adapted plan was selected in 78% of fractions. oART improved target coverage in 76% of fractions. D mean decreased for the oral cavity (−2.4 Gy, p < 0.001) but increased for the middle PCM (2.5 Gy, p < 0.001). D max increased for the brainstem (2.9 Gy, p < 0.001) and spinal cord (2.2 Gy, p < 0.001). Intrafractional motion was within PTV margins, with few patient-specific exceedances. Conclusion Daily oART for HNC is feasible with improvements in target coverage but modest and inconsistent OAR sparing.