Abstract Purpose In head and neck (H&N) radiotherapy, an essential requirement is the reproducibility of the relative position of head and neck during the whole treatment. Moreover, adaptive radiotherapy for… Click to show full abstract
Abstract Purpose In head and neck (H&N) radiotherapy, an essential requirement is the reproducibility of the relative position of head and neck during the whole treatment. Moreover, adaptive radiotherapy for H&N cancer would benefit from indicators capable of easily identifying morphological alterations. Aim of this study was to test whether the immobilization device guarantees a reproducible head and neck position and to identify, on set-up verification images, some indicators capable of describing morphological alterations. Methods and materials A retrospective analysis on 15 patients immobilized using s-shaped head-neck-shoulders masks and treated with TomoTherapy (50–70 Gy/25-33fr) was conducted. For each treatment session two MVCT-CT registrations were performed alternatively optimizing matching on the head or the neck. For each patient mean differences between the two registrations parameters ( Δ x, Δ y, Δ z, Δ pitch, Δ roll, Δ yaw) over all treatment sessions were evaluated. Morphological alterations were studied (once a week for the whole treatment duration) by measuring on MVCT images the skin-to-skin distance at 3 different antero-posterior levels: at the center of parotid glands (line1) and 2 cm (line 2) and 4 cm (line 3) anteriorly. Mean percentage variations respect to the first week were evaluated for all patients. A Student’s t-test was carried out (p Results Mean differences between head and neck registration parameters are reported in Table 1 . Except for two patients, mean differences were smaller than 1.7 mm and 1.2°. Mean percentage variations of lines’ length are reported in Fig. 1. For all, a decreasing trend was observed. Variations are statistically significant starting from the 4 th week for lines 1 and 2, and only from the 6 th week for line 3. Conclusion The immobilization device enables adequate H&N set-up during the whole treatment for almost all patients. Lines 1 and 2 drawn on MVCT images seem to be suitable for describing morphological alterations that might deserve re-planning.
               
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