Oral contrast agents lead to underestimation of dose calculation in volumetric-modulated arc therapy planning for pelvic irradiation  

作　　者：Hao Jing Yuan Tian Yu Tang Shu-Lian Wang Jing Jin Yong-Wen Song Yue-Ping Liu Hui Fang Bo Chen Shu-Nan Qi Yuan Tang Ning-Ning Lu Yong Yang Ning Li Ye-Xiong Li 

机构地区：[1]Department of Radiation Oncology,National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College,Beijing 100021,China

出　　处：《Chinese Medical Journal》2020年第17期2061-2070,共10页中华医学杂志（英文版）

基　　金：This work was supported by the grants from the National Key Projects of Research and Development of China(No.2016YFC0904600);the Beijing Municipal Science&Technology Commission of China(No.Z171100001017116)。

摘　　要：Background:The effects of oral contrast agents(OCAs)on dosimetry have not been studied in detail.Therefore,this study aimed to examine the influence of OCAs on dose calculation in volumetric-modulated arc therapy plans for rectal cancer.Methods:From 2008 to 2016,computed tomography(CT)images were obtained from 33 rectal cancer patients administered OCA with or without intravenous contrast agent(ICA)and 14 patients who received no contrast agent.CT numbers of organs at risk were recorded and converted to electronic densities.Volumetric-modulated arc therapy plans were designed before and after the original densities were replaced with non-enhanced densities.Doses to the planned target volume(PTV)and organs at risk were compared between the plans.Results:OCA significantly increased the mean and maximum densities of the bowels,while the effects of ICA on these parameters depended on the blood supply of the organs.With OCA,the actual doses for PTV were significantly higher than planned and doses to the bowel increased significantly although moderately.However,the increase in the volume receiving a high-range doses was substantial the absolute change of intestine volume receiving≥52 Gy:1.46[0.05-3.99,cubic centimeter range:-6.74 to 128.12],the absolute change of colon volume receiving≥50 Gy:0.34[0.01-1.53 cc,range:-0.08 to 3.80 cc].Dose changes due to ICA were insignificant.Pearson correlation showed that dose changes were significantly correlated with a high intestinal volume within or near the PTV(ρ>0.5,P<0.05)and with the density of enhanced intestine(ρ>0.3,P<0.05).Conclusions:Contrast agents applied in simulation cause underestimation of doses in actual treatment.The overdose due to ICA was slight,while that due to OCA was moderate.The bowel volume receiving≥50Gy was dramatically increased when OCA within the bowel was absent.Physicians should be aware of these issues if the original plan is barely within clinical tolerance or if a considerable volume of enhanced intestine is within or near the PTV.

关 键 词：Oral contrast agents Simulation DOSIMETRY Organ at risk Volumetric-modulated arc therapy 

分 类 号：R730.55[医药卫生—肿瘤]