鼻咽癌调强适形放疗中正常器官体积剂量变化的研究

Changes of volume dose of normal organs in IMRT for nasopharyngeal carcinoma

目的运用重复CT扫描和重新设计计划,观察鼻咽癌患者在调强放疗过程中正常器官体积及剂量的变化。方法选择接受全程调强放疗的首治鼻咽癌患者20例,鼻咽、颈部和锁骨上区均采用IMRT技术,按IMRT步骤设计计划1得到DVH1。患者在放疗20次时,按原固定体位和参考坐标重新CT扫描,拷贝计划1至重新勾画的靶区产生计划1-2和DVH1-2,对第2次CT扫描重新进行设计得到计划2并得到DVH2。应用DVH图对放疗前和放疗20次时正常器官的体积剂量进行比较分析。结果与计划1相比较,计划1-2左右腮腺体积明显小于DVH1(P<0.05),左右腮腺的最大剂量、平均剂量、D50和V35,脊髓的最大剂量、平均剂量和Dlcc均明显增加(P<0.05),脑干最大剂量增加(P=0.011),腮腺的剂量增加与放疗所致的体质量下降、轮廓减少和腮腺体积缩小程度密切相关,脊髓的最大剂量增加与左右轮廓减少程度有一定的相关性(r=0.469,P=0.037)。结论鼻咽癌IMRT过程中正常器官体积剂量会发生一些变化,特别是腮腺变化比较明显,建议放疗中后期有必要重新勾画靶区,重新计划,以减小正常器官的受照射量和放疗反应。

Objective To investigate the changes of the volume dose of normal organs in intensity modulated radiotherapy for nasopharyngeal carcinoma through repeated CT imaging and replanning.Methods This study enrolled twenty patients with nasopharyngeal carcinoma who were treated by intensity modulated radiotherapy（IMRT） as the first-line treatment,nasopharynx,cervical part and supraclavicular region were all treated by IMRT;we designed the first IMRT plan（plan1）and formed DVH1.CT-simulated image was rebuilt at the same body position at the twentieth time during radiotherapy,and plan1 was copied to the second CT-simulated image and generated plan1-2 and DVH1-2.we redesigned the second CT-simulated image and formed plan2,The data obtained from CT-simulated image and DVH were analyzed terms of in the vanations of normal organ volume dose between before and the twentieth treatment.Results The volume of plan1-2 about the left and right parotids were much decreased compared with plan1（P0.05）.The maximum dose,mean dose,D50 and V35 of parotid glands,the maximum dose,mean dose and Dlcc of spinal cord obviously increased（P0.05）.There was statistical difference in the maximum dose of brain stem（P=0.011）;the parotid′s augmented dose correlated with the shrunken degree of weight,left and right contour and parotids;and the maximum dose of spinal cord correlated with left and right contour（r=0.469,P=0.037）;and other normal organs have no difference.Conclusion There were some changes of the normal organs volume dose in IMRT for nasopharyngeal carcinoma,especially for parotid glands.It was requisite to rebuild CT-simulated image and renew plan during midanaphase treatment to reduce radiated dosage and avoid radiotherapy reaction.