Radiotherapy
Helical tomotherapy (HT) was delivered once daily, 5 days per week, as
previously described [5]. In brief, the planning dose at D95 (dose
received by 95% of the target volume) was set at 67.5 grays (Gy) for
the planning gross target volume of the primary tumor (pGTVnx) and the
planning gross target volume of the metastatic lymph node (pGTVnd). The
planning target volume (PTV) was set at 60 Gy and the PTV2 was set at 54
Gy in 30-33 fractions. No more than 5% of PTV volume received more than
110% of the prescribed dose. Dose-volume constraints for organs at risk
(OARs) were set as follows: (1) parotid gland V30 <50% or
Dmean ≤28 Gy; (2) brainstem Dmax ≤54 Gy; (3) spinal cord Dmax ≤45 Gy;
(4) optic nerve Dmax ≤54 Gy; (5) temporo-mandibular joint Dmax ≤60 Gy;
and (6) lens Dmax ≤5 Gy. HT plans were developed for a field width of
2.5 cm, a pitch of 0.30–0.38, and a modulation factor equal to
2.0–3.0. During radiation therapy, patients underwent megavoltage
computed tomography (MVCT) imaging at least once each week to verify
patient setup. The imaging frequency was determined by the magnitude of
setup errors from initial daily scans. Carotid radiotherapy dose was the
same among different groups.