EFFECTIVE DOSES ASSOCIATED WITH CT EXAMINATIONS AND RADIATION INDUCED LIFETIME CANCER RISK ESTIMATION
Abstract
Background
Computed Tomography (CT) examinations are increased significantly over the past three decades. However CT contributed substantially higher radiation doses as compared to conventional x-ray procedures. In this study, the radiation doses are estimated for head and chest CT procedures and calculated the cancer risks on the basis of measured doses.
Material and Methods
CT doses are estimated by using scanner derived parameters and thermo luminescent dosimeters (TLD) for head and chest CT procedure. TLD chips were placed on the exposed area of the selected patients and one TLD for each patient placed outside the field to measure the scattered radiation. Age, weight and height of all selected patients were recorded. To evaluate the TLD dose, exposed TLDs were read with TLD reader.
Results
Mean doses of male and female patient for head CT procedure measured with CT generated dose index and TLD were 57.59 ± 2.354 mGy and 47.1 ± 5.35 mGy respectively. Mean doses for chest scan generated with CT dose index was 8.82 ± 2.09 mGy and measured with TLD came out to be 15.73 ± 5.2 mGy. The mean effective doses calculated for CT and TLD were 2.0 ± 0.579 mSv and 0.443 ± 0.043 mSv during head CT procedure and 5.6 ± 0.913 mSv and 1.7 ± 0.754 mSv found for chest CT examination. Based on measured data lifetime excess cancer risks for head and chest CT were calculated.
Conclusion
Radiation doses measured from selected procedures in diagnostic CT examinations were lower than the recommended dose limits and variable within the same examinations. The calculated doses from CT derived parameters and TLD do not exceed the recommended safe limits for head and chest CT procedures.
References
Mettler FA Jr, Thomadsen BR, Bhargavan M et al. Medical radiation exposure in the U.S. in 2006: preliminary results. Health Physics 2008; 95 (5): 502- 507.
Wiest PW, Locken JA, Heintz PH, Mettler FA. CT scanning: a major source of radiation exposure. Semin Ultrasound CT MR. 2002; 23(5):402-410.
Lewis MA, Edyvean S. Patient dose reduction in CT. Br J Radiol. 2005; 78:880–883.
Gonzalez AB, Mahesh M, Kim KP et al. Projected cancer risks from computed tomography scans performed in the United States in 2007. Arch Inter Med. 2009; 169 (22):2071-77.
Shrimpton PC, Hillier MC, Lewis MA, Dunn M. Doses from computed tomography (CT) examinations in the UK-2003 review (NRPB-W67) Chilton: NRPB; 2005.
Olerud HM. Analysis of factors influencing patient doses from CT in Norway. Radiat Prot Dosimetry. 1997; 71:123–133.
BEIR-VII. Biological Effects of Ionizing Radiation. Health risks from exposure to low levels of ionizing radiation. National research Council, National Assembly Press 2005.
Aldrich JE, Bilawich AM, Mayo JR. Radiation doses to patients receiving computed tomography examinations in British Columbia. Can Assoc Radiol J. 2006; 57: 79-85.
ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann. ICRP 2007; 37: 2-4.
Tack Group on Control of Radiation Dose in Computed Tomography. Managing patient dose in Computed Tomography. A report of the ICRP. Ann ICRP. 2000; 30:7-45.
Brenner DJ, Elliston CD. Estimated radiation risks potentially associated with full body CT screening. Radiol. 2004; 232(3): 735-738.
Commission of the European Community. European guidelines on quality criteria for computed tomography. 1999. Report EUR 16262 EN.
UNSCEAR 2000. The United Nations Scientific Committee on the Effects of Atomic Radiation. Report to the General Assembly. New York United Nations 2000.
