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 (Dmean) and maximum dose (Dmax) 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. Dmean decreased for the oral cavity (-2.4 Gy, p < 0.001) but increased for the middle PCM (2.5 Gy, p < 0.001). Dmax 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.