Background: Long term exposure to environmental radioactivity and the associated external exposure due to gamma emitting radionuclides have serious health effects particularly on cancer risk. Of course, the soil radioactivity depends on the underlying rocks and consequently, the soil type and the geographic conditions. Objectives: Evaluation of excess life time cancer risk due to natural radioactivity of the soil of surface layer of the Nichahoma lignite belt and the soil of villages surrounding the lignite belt. 226 232 40 Methods: In this particular study, stirring radionuclides of the Ra , Th , and K present in the soil samples of the lignite belt and soil of the villages surrounding the lignite belt were measured by using a low-background Pb-shielded gamma spectroscopic counting assembly utilizing NaI(Tl) detector for the measurement and to evaluation the radiation hazard indices and excess life time cancer risk. -3 -3 -3 -3 Results: The excess life time cancer ranged from 0.65×10 to 0.71× 10 (average ~0.68×10 ) for the soil of the lignite belt and from 1.15×10 to -3 -3 1.34×10 (average ~1.25×10 ) for the soil of the villages surrounding the belt. The correlation analyses, performed between the radium equivalent activity and excess life time cancer risk for the two types of the sample, showed very strong and linear dependence of excess life time cancer risk on radium equivalent activity and measured dose rate for the soil of the lignite belt compared to the soil of the villages surrounding the lignite belt. Conclusion: Compared to world average, the average value of computed excess life time cancer risk for both the categories of investigated samples in the study was found to be higher than 0.29. JMS 2018: 21 (2):101-108 Keyword: Excess life time cancer risk, measured dose rate, radium equivalent activity, correlation analysis, lignite belt.

The study aimed to compute the effective dose (E) and size-specific dose estimate (SSDE) of routine adult patients undergoing thorax and abdominal computed tomography (CT) imaging and to present their multivariate analysis. All adult thorax and abdominal CT examinations conducted from March 2022 to June 2022 were prospectively included in this study. The Water Equivalent Diameter (Dw ) and SSDE of all the examinations were computed from CT dose index volume (CTDIvol ) and Dose length product (DLP) displayed on the dose report in the CT console. The multivariate statistical analysis was performed to investigate the correlation of SSDE and E on CTDIvol , Dw area of the region of interest (ROI) (AreaROI ), body mass index (BMI), conversion factor (fsize) and hounsfield (HUmean ) number in the ROI at 95% level of significance (P < 0.05). The linear regression analysis was performed to investigate the dependence of SSDE and E on other parameters for both abdominal and thorax patients. A total number of 135 (Abdomen = 61 and Thorax = 74) measurements were performed. The mean value of effective dose for abdomen and thorax patients was found to be 7.17 ± 3.94 and 4.89 ± 2.16 mSv, respectively. The SSDE was observed to be 13.24 ± 3.61 and 13.04 ± 3.61 mGy for thorax and abdomen respectively. The multivariate analysis suggests that SSDE for abdominal CT is found significantly dependent on CTDIvol , Dw and fsize with P < 0.05 and E is found to be significantly dependent on DLP, AreaROI , Dw and fsize at 95% level of confidence for abdominal CT imaging. SSDE for thorax CT was found significantly dependent on BMI, CTDIvol , HUmean , Dw and fsize at 95% level of confidence. Furthermore, E was observed dependent on DLP at P < 0.05. The linear regression analysis also shows that E is strongly correlated with DLP (r = 1.0) for both thorax and abdominal CT, further the SSDE was observed strongly correlated with CTDIvol with r = 0.79 and r = 0.86 for abdomen and thorax CT respectively. A strong correlation was observed between BMI and for Dw abdominal CT imaging (r = 0.68). The mean value of SSDE for thorax is slightly greater than abdomen. The average value of effective dose for abdomen and thorax measurements was found to be 7.17 ± 3.94 and 4.89 ± 2.16 mSv and , correspondingly. SSDE for both abdomen and thorax CT is significantly dependent on CTDIvol , Dw and fsize at 95% level of confidence. The strong correlation was also observed E on DLP and SSDE on CTDIvol for both Abdomen and Thorax CT. The strong dependence of Dw on BMI (r = 0.68) is due to the excessive fat concentration around the stomach and abdomen.