Radiation skin doses to patients undergoing abnomal computed tomographic examinations

Abstract

Radiation is always a medical concern as it may induce cancer and hereditary defects ..The use of CT has increased rapidly in the past decade due to the increased medical diagnostic applications of this imaging modality. This has resulted in an increasing medical radiation burden associated with CT. Doses should therefore be kept as low as reasonably achievable in line with the ALARA principle. Objective: The main objective of the study was to generate baseline data in patients' radiation skin doses during abdominal CT scan examination and to assess the associated risks to certain critical organs. Study Design: The study was comparative and cross sectional. Study Setting: The study was conducted at MITC and involved eighty-one patients who presented for-C'T scan examinations of the abdomen between September 2002 and March 2003. Subject/Patients: Eighty-one patients presented for abdominal CT examinations. Thirty-five patients underwent conventional CT examination at MP Shah while thirty-six patients underwent spiral CT examination at MITC. Ten patients were assessed for radiation skin dose during topogram examination at MP Shah. Method: Radiation doses were measured by use of Thermolumiscent Dosimeters (Lithium Fluoride), which were placed before the CT scan examination on the skin corresponding to the Thyroid gland, Liver, Breasts and Testis. The amount of radiation absorbed by the dosimeters was determined by reading their light output in the Thermoluminiscent Dosimeter Reader at the Department of Diagnostic radiology (U.O.N). The dosimeters were earlier calibrated using cobalt-60 radiation to determine their response to a certain uniform amount of radiation. Results: Dose calculations for each region e.g. liver, breast, thyroid, and testis were done for each patient. Data was entered into a microcomputer using SPSS/PC data entry programme. Geometric means for radiation dose to the various skin sites were calculated. The results showed that mean dose was highest for liver (sequential CT- 88.8mGy, spiral CT-92.8mGy), followed by Breast (sequential- 9.89mGy, Spiral-lOmGy), Thyroid (sequential-2.85mGy, Spiral- 2.52mGy) and was lowest for the Testis (sequential-l.23mGy, Spiral-l.33mGy). Results also showed that there was no significant difference in skin doses delivered during conventional and spiral CT examination. The dose delivered by Topogram examination relative to the multi-slice examination were insignificant to the liver, breast, and thyroid while it was significant to the testis denoting that the topogram contributed to most of the testis skin dose. Conclusion There was no significant difference in skin doses at sequential or spiral CT examinations. The skin doses in this study were generally below radiation dose levels required to induce deterministic effects like causing temporary or permanent sterility of the testis. The choice of whether to use spiral or conventional CT should therefore rely on clinical considerations rather than on dose.