RESUMO
BACKGROUND AND PURPOSE: The impact of weight loss and anatomical change during head and neck (H&N) radiotherapy on spinal cord dosimetry is poorly understood, limiting evidence-based adaptive management strategies. MATERIALS AND METHODS: 133 H&N patients treated with daily mega-voltage CT image-guidance (MVCT-IG) on TomoTherapy, were selected. Elastix software was used to deform planning scan SC contours to MVCT-IG scans, and accumulate dose. Planned (DP) and delivered (DA) spinal cord D2% (SCD2%) were compared. Univariate relationships between neck irradiation strategy (unilateral vs bilateral), T-stage, N-stage, weight loss, and changes in lateral separation (LND) and CT slice surface area (SSA) at C1 and the superior thyroid notch (TN), and ΔSCD2% [(DA - DP) D2%] were examined. RESULTS: The mean value for (DA - DP) D2% was -0.07â¯Gy (95%CI -0.28 to 0.14, range -5.7â¯Gy to 3.8â¯Gy), and the mean absolute difference between DP and DA (independent of difference direction) was 0.9â¯Gy (95%CI 0.76-1.04â¯Gy). Neck treatment strategy (pâ¯=â¯0.39) and T-stage (pâ¯=â¯0.56) did not affect ΔSCD2%. Borderline significance (pâ¯=â¯0.09) was seen for higher N-stage (N2-3) and higher ΔSCD2%. Mean reductions in anatomical metrics were substantial: weight loss 6.8â¯kg; C1LND 12.9â¯mm; C1SSA 12.1â¯cm2; TNLND 5.3â¯mm; TNSSA 11.2â¯cm2, but no relationship between weight loss or anatomical change and ΔSCD2% was observed (all r2â¯<â¯0.1). CONCLUSIONS: Differences between delivered and planned spinal cord D2% are small in patients treated with daily IG. Even patients experiencing substantial weight loss or anatomical change during treatment do not require adaptive replanning for spinal cord safety.