Study on dosimetric difference of organ at risk between actual estimated receiving and pretreatment plan during intensity-modulated radiotherapy for nasopharyngeal carcinoma / 中华放射肿瘤学杂志

ABSTRACT

Objective To investigate the dosimetric difference of organ at risk (OAR) for planning and actual estimated during intensity-modulated radiotherapy (IMRT) for patients with nasopharyngeal carcinoma.Methods Thirteen patients were enrolled to accept full course of IMRT.CT scans were acquired in the 10th,20th,and 30th fractions during radiotherapy,respectively.OAR,including brain stem,spinal cord,parotid gland and submandibular gland,were delineated on repeated CT scans.The volume change of OAR were investigated.After that,the plans were copied to the new CT image to calculate the escalated average dose of OAR during radiotherapy (Actual estimated receiving dose minus planning dose).Results The change trend of volume was decreasing gradually for parotid gland and submandibular gland during the 10th,20th,and 30th times radiotherapy (all P =0.000).The maximum dose (Dmax) of brain stem and spinal cord and the 50％ volume receiving dose (D50) of parotid gland increased significantly in the 10th,20th,and 30th times during radiotherapy,respectively.The escalated average dose were 3.76 and 3.68 Gy for Dmax of brain stem and spinal cord (P =0.000,0.000),5.11 and 3.54 Gy for D50 of left and right parotid (P =0.001,0.023),and 0.49 and 0.75 Gy for D50 of left and right submandibular gland (P =0.220,0.230),respectively.Conclusions The volume of parotid gland and submandibular gland significantly decreased after radiotherapy The actual receiving dose of brain stem,spinal cord,and parotid gland increased significantly during radiotherapy.However,there was no significant change for the actual receiving dose of submandibular gland.