Volume and dosimetric changes and initial clinical experience of a two-step adaptive intensity modulated radiation therapy (IMRT) scheme for head and neck cancer

Abstract

PurposeThe aim of this study was to show the benefit of a two-step intensity modulated radiotherapy (IMRT) method by examining geometric and dosimetric changes. Material and MethodsTwenty patients with pharyngeal cancers treated with two-step IMRT combined with chemotherapy were included. Treatment-planning CT was done twice before IMRT (CT-1) and at the third or fourth week of IMRT for boost IMRT (CT-2). Transferred plans recalculated initial plan on CT-2 were compared with the initial plans on CT-1. Dose parameters were calculated for a total dose of 70Gy for each plan. ResultsThe volumes of primary tumors and parotid glands on CT-2 regressed significantly. Parotid glands shifted medially an average of 4.2mm on CT-2. The mean doses of the parotid glands in the initial and transferred plans were 25.2Gy and 30.5Gy, respectively. D2 (dose to 2% of the volume) doses of the spinal cord were 37.1Gy and 39.2Gy per 70Gy, respectively. Of 15 patients in whom xerostomia scores could be evaluated 1–2years after IMRT, no patient complained of grade 2 or more xerostomia. ConclusionsThis two-step IMRT method as an adaptive RT scheme could adapt to changes in body contour, target volumes and risk organs during IMRT.