鼻咽癌IMRT中OAR实际受量与计划剂量差异研究

Study on dosimetric difference of organ at risk between actual estimated receiving and pretreatment plan during intensity-modulated radiotherapy for nasopharyngeal carcinoma

目的观察鼻咽癌IMRT中OAR实际受量估算值与计划剂量的差异。方法选取13例拟接受IMRT鼻咽癌患者，在放疗第10、20、30次时重新cT扫描，并勾画脑干、脊髓、左右腮腺和颌下腺，观察其体积在放疗中的变化。将放疗前治疗计划复制到每个新的cT图像上，计算整个放疗中估算增加的剂量（实际受量估算值减去物理计划剂量）。结果放疗第10、20、30次时左、右腮腺及颌下腺体积在放疗过程呈进行性下降（P值均为0．000）。与计划剂量相比，整个放疗过程脑干、脊髓的Dmax 分别平均增加3．76、3．68Gy（P=0．000、0．000），左、右腮腺的D50 分别平均增加5．11、3．54Gy（P=0．001、0．023），左、右颌下腺的D50分别平均增加0．49、0，75Gy（P=0．220、0．230）。结论鼻咽癌放疗过程后腮腺和颌下腺体积明显缩小。脑干、脊髓和腮腺实际受量较计划剂量显著增加，而颌下腺受量变化不明显。

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.