ABSTRACT
Objective To analyze the anatomic changes and dosimetric variations of patients with head-and-neck cancer during intensity-modulated radiotherapy and to assess the necessity of re-planning the treatment course.Methods Twenty-one nasopharyngeal carcinoma patients were selected to receive the second CT scan in the course of intensity-modulated radiotherapy,targets and organs at risk were re-contoured on the new CT images with the help of deformable registration software.Actual dose distribution delivered by the original treatment plan was calculated on the second CT image,and then the volume and doses of targets and organs at risk were compared between the planning CT and second CT.Results The volume of patient's head-and-neck outlines and GTVnd decreased significantly,the volume of cord and brainstem didn't change much,while the volume of left and right parotids decreased significantly by (24.23 ± 12.15)％ and (25.82± 10.46)％,respectively.The parameters D95％ and Dmean of PGTVnx kept stable,but the parameters D1cc of spinal cord PRV and brainstem PRV increased by (8.12± 10.32)％ and (14.60±18.85)％ respectively.The mean dose of the left and right parotids increased significantly by (27.43±17.67)％ and (26.76±12.46)％,respectively.Conclusion The anatomical changes of patients undergoing intensity-modulated radiotherapy will cause significant dosimetric variations of the cord,brainstem and parotids,so it's meaningful and necessary to re-design the treatment plan in the course of radiotherapy.Repeat CT imaging and replanning during the course of IMRT is essential to ensure adequate doses to target volumes and safe doses to normal tissue.