RESUMO
Objective To estimate the lifetime attributable risk (LAR) of lung cancer,stomach cancer,liver cancer,thyroid cancer,breast cancer and leukemia for 1-,5-and 10-year old children undergoing chest CT scan.Methods Chest CT images of children was retrieved from the picture archiving and communication system (PACS) and the average CT number and area of the region of interest (ROI) were read on the CT work station.Water equivalent diameter were calculated according to the method recommended by the American Association of Physicists in Medicine (AAPM).Furthermore,the size-specific dose estimation (SSDE) was made based on the water equivalent diameter and the volume computed tomography dose index(CTDIvol).Based on the method recommended by Caro Franck,the SSDE then was converted into average organ doses to lung,stomach,liver,thyroid,breast and blood for children at different ages and of different sex undergoing chest CT scan.On the basis of average organ dose,the cancer risk prediction model from the National Academy of Science's Biological Effects of Ionizing Radiation-Ⅶ (BEIR-Ⅶ) was used to predict the LAR for different cancers mentioned above.For lung cancer,gastric cancer,liver cancer and leukemia,the calculating sequence was from average organ dose to excess relative risk (ERR) to LAR,whereas for the thyroid cancer and breast cancer,the sequence was from ERR to average organ dose to LAR.Results The average organ dose to lung,stomach,liver,thyroid,breast and blood for children at different age and of different sex undergoing chest CT scan was obtained.The age had a statistically significant impact on the SSDE (t =24.28,P ＜ 0.05),but sex has not (P ＞ 0.05).LAR for lung cancer,gastric cancer,liver cancer,thyroid cancer,breast cancer and leukemia for 1-,5-and 10-year old children undergoing chest CT scan was obtained,among whom the LAR for thyroid cancer and breast cancer was relatively high.The LAR for women breast cancer was 10.9 per 100 000 persons for 1 year old children,30.8 per 100 000 persons for 5 years old and 34.5 per 100 000 persons for 10 years old.Conclusions With introduction of new technologies,the radiation dose due to chest CT scan is on the decline.But the induced radiation dose is still significant compared with general diagnostic radiography.The risk of cancer still deserves more attention and should be taken into consideration in the justification of diagnostic radiology.
RESUMO
OBJECTIVE: To quantify the cumulative effective dose (cED) of radiation due to repeated CT and PET/CT examinations after curative resection of gastric cancer and to assess the lifetime attributable risk (LAR) estimates based on Biological Effects of Ionizing Radiation VII models. SUBJECTS AND METHODS: Patients who underwent a curative resection for gastric cancer between January 2006 and December 2006 and were followed-up until May 2010 were included in this study. The cED was calculated by using the dose-length product values and conversion factors for quantitative risk assessment of radiation exposure. cED and LAR were compared between early and advanced gastric cancer patients and among American Joint Committee on Cancer TNM stage groups (stage I, II, and III). The nonparametric Mann-Whitney U and Kruskal-Wallis tests, followed by a post-hoc analysis with Bonferroni adjustment, were employed as part of the statistical analysis. RESULTS: The overall median cED was 57.8 mSv (interquartile range [IQR], 43.9-74.7). The cED was significantly higher in the advanced (median, 67.0; IQR, 49.1-102.3) than in the early gastric cancer group (median, 52.3; IQR, 41.5-67.9) (p < 0.001), and increased as the TNM stage increased. For radiation exposure, 62% of all patients received an estimated cED of over 50 mSv, while 11% of patients received over 100 mSv. The median LAR of cancer incidence was 0.28% (IQR, 0.20-0.40) and there were significant differences between the early gastric cancer and advanced gastric cancer group (p < 0.001) as well as among the three TNM stage groups (p = 0.015). The LAR of cancer incidence exceeded 1% in 2.4% of the patients. CONCLUSION: The cED increases proportionally along with tumor stage and, even in early gastric cancer or stage I patients, cED is much higher than that found among the general population. Considering the very good prognosis of early gastric cancer after curative surgery, the cED should be considered when designing a postoperative follow-up CT protocol.