Geometric changes to the central nervous system organs at risk during chemoradiotherapy for locally advanced nasopharyngeal carcinoma

BackgroundConsiderable geometric changes to the organs at risk (OARs) have been reported during treatment with chemotherapy and intensity modulated radiotherapy (chemo-IMRT) for locally advanced nasopharyngeal carcinoma (LA-NPC). This study aimed to quantify geometric changes to the central nervous system-related OARs (CNS-OARs), during chemo-IMRT for LA-NPC. MethodsThis prospective study included 20 patients with LA-NPC, treated with chemo-IMRT. Patients underwent a planning computed tomography (CT-plan) scan with intravenous contrast, followed by six weekly scans without contrast (CT-rep). For CNS-OARs, including the spinal cord, brainstem, optic chiasm and nerves, the globes of the eye, lens, and inner ears, their volume loss, the center of mass (COM) displacement, and spatial deformation was compared among weeks, respectively. The correlation between organ volume reduction and patients weight loss was estimated. ResultsThe volume of the brainstem, spinal cord, and the globe of left-and right-side eye averagely decreased by 2.6{+/-}2.3% (95% CI: 2.1%, 3.1%), 6.5{+/-}4.8% (5.6%,7.4%), 9.4{+/-}6.9% (8.1%, 10.6%) and 9.6{+/-}7.8% (8.2, 11.1%) respectively. The volume reduction of the spinal cord and that of the brainstem were significantly correlated with patients weight loss. For all OARs, the COM displacement was within 3 mm, except for the lower level of the spinal cord. The DSC value of the spinal cord, brainstem, and the globes of the eye was of >0.85 throughout treatment. ConclusionsThe volume and shape changes to the CNS-OARs during chemo-IMRT for NPC were quantifiable, which could be useful to refine radiation treatment protocols.