Abstract 853: Investigation of the cumulative number of chromosome aberrations induced by three consecutive CT scans
Authors: Abe Yu , Noji Hideyoshi , Sugai Misaki , Kurosu Yumiko , Ohba Takashi , Yanagi Aki , Yanai Yukari , Tsuyama Naohiro , Ishikawa Tetsuo , Miura Tomisato , Kamiya Kenji , Yoshida Mitsuaki A. , Sakai Akira 
Published: August 2018

Abstract
Purpose The relationship between radiation exposure by CT and the risk of leukemia and brain tumor has been reported in children, in which the risk of leukemia was tripled at a radiation dose of 60 mGy to bone marrow (Pearce MS, Lancet 2012). Therefore, there is a possibility that CT scans induce chromosome aberrations (CAs) causing malignant tumors. When chromosomes are cleaved by radiation, dicentric chromosomes (Dics) and chromosome translocations (Trs) are formed in the same ratio. We have reported that breakage of chromosomes was induced after a single CT scan in adults by Dic assay (DCA) (Scientific Rep 2015). On the other hand, the number of Trs formed also increased after a single CT scan, but, no significant change of the numbers was observed before and after the CT scan (J Rad Res 2016). We then investigated whether cumulative CAs would be observed when an annual CT scan was performed for 3 years.
Methods Peripheral blood samples were collected from 5 patients (4 males and 1 female; age range 51-73 years; mean age, 64 years) 3 times before and after a CT scan at annual examinations. They included 4 patients with malignant lymphoma who had not been treated for more than 3 years after the end of treatment and 1 patient followed due to an abnormal lung shadow without treatment. We performed analysis of Dic and Tr formation by centromere-FISH and painting-FISH using isolated lymphocytes, respectively, and counted the number of CAs equivalent to 2,000 metaphases per sample. The effective radiation dose of a CT scan was calculated by computational dosimetry system (WAZA-ARI).
Results Regardless of CT scans, the number of Trs formed was higher than that of Dics in all patients. The dose of radiation exposure in one CT scan was 22.0 to 73.5 mSv (mean, 42.3 mSv). Both DCA and Tr analyses showed an increase in Dic and Tr formation after all CT scans, except that their number decreased in one patient after the second CT scan. However, the increase in these CAs decreased after about one year, and no cumulative increase in the number of Dics and Trs formed due to three consecutive CT scans was observed.
Conclusion A single CT scan tended to produce both Dic and Tr formation, but there was no cumulative increase in CAs after three consecutive CT scans. The reason that the number of Trs formed was basically higher than that of Dics is considered to be related to such factors as age, smoking status, and past medical radiation exposure especially in adults because Tr is a stable chromosome.
Citation Format: Yu Abe, Hideyoshi Noji, Misaki Sugai, Yumiko Kurosu, Takashi Ohba, Aki Yanagi, Yukari Yanai, Naohiro Tsuyama, Tetsuo Ishikawa, Tomisato Miura, Kenji Kamiya, Mitsuaki A. Yoshida, Akira Sakai. Investigation of the cumulative number of chromosome aberrations induced by three consecutive CT scans [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 853.