19 Cumulative Radiation Effective Dose

The CT scanners on the market offer a multitude of procedure protocols that enable many clinical questions to be answered quickly. CT scanners can be used to image all parts of the body, some common uses in our hospital include; acute inflammatory bowel diseases; acute appendicitis, trauma including head, spine and skeletal trauma, renal diseases including congenital, inflammatory and neoplastic, temporal bone diseases, neck swelling, diagnosing and staging cancer (using PETCT when appropriate) and planning radiotherapy treatment (using PETCT when appropriate). Whatever the reason for a procedure a radiation dose is associated with the exam and this can range from a relatively small to a relatively large amount depending on the clinical requirements of the diagnostic test. Since x-rays have the potential to damage cells in the body and there is no “safe” dose of radiation, the body’s exposure to radiation should be kept to a minimum, a challenging task for CT imaging. The radiation effective dose is a calculated quantity that is intended to give an estimate of the relative biological detriment resulting from a radiation exposure and is measured in units called Sieverts (Sv). As the x-ray tube rotates around the patient it takes hundreds of x-ray pictures of a thin section of the body. In one rotation the “thin section” is determined by the number of detector rows and their collimation. Many rotations around the patient result in large body volumes being imaged. The images obtained from each section can be reconstructed to any slice width down to the width of the collimation of a single detector. Technological advances in CT scanners have seen increases in the number of slices and detector rows leading to wider coverage of the patient anatomy per rotation of the x-ray tube around the patient. Helical scanners have led to even greater coverage of the patient anatomy in faster examinations. However, CT procedures are inherently high radiation effective dose procedures, although the actual scanning takes from a few seconds to a few minutes, depending on the examination and type of scanner, it’s easy to lose track of the actual radiation exposure to the patient. The images obtained from CT provide much more diagnostic information than conventional radiographs or fluoroscopy but the radiation effective doses are much higher than for other x-ray exams.