Radiation dose from CT scanning: can it be reduced?

Vol. 5 No. 1February 2011Radiation dose from CT scanning19These data show a wide range of CT dosesbetween hospitals in Thailand for each type of CTscan. The effective dose of CT brain ranges from2.5-5 mSv, CT chest from 5.1-10.1 mSv, CT upperabdomen from 15.2-19.4 mSv, and CT wholeabdomen from 14.7-26.1 mSv.With multiple scans to the same area (pre contrastand post contrast scans) in one examination, the patientdose increased to double when the same scanningparameters and same scan length were used. Singleseries of non-contrast CT brain may be adequate forpatients with specific clinical indications. This wasapplied in more than half of CT brains in Hospitals Aand B. As non-enhanced CT chest usually givesinadequate information, Hospitals A and E prefer postenhanced CT chest, and Hospital C performed a limitedlength of pre contrast scan to reduce the unnecessaryradiation.The high total dose is more obvious with CTabdomen, where the scanning area is long (25 cm forupper abdomen and 45 cm for the whole abdomen).There is a high conversion coefficient (many organswith high tissue weighting factors in the abdomen)and multiple phases of scanning (depending on clinicalquery). The high dose setting is seen in high CTDI ofCT abdomen in Hospital D. Multiphase scan explainshigh dose for CT abdomen in Hospital A.Comparing dose parameters in Thailand to DRLsfrom the UK and European Commission, we foundthat mean CTDI values in Thailand were not abovetheir level. However, mean DLP value of some typesof CT scanning in many hospitals was above thelevels. This is likely from greater extension of the scanlength. Orbits and maxillary sinuses are mostlyincluded in brain-scanned areas including the sensitiveeye lenses.Patient’s information is a necessary part inplanning a proper CT scan, particular the numbers ofscanning phases. Discussion between physician andradiologist beforehand may obviate unnecessaryscanning phases or may move the patient to anothermore appropriate imaging modality. With inadequatecommunication between attending doctor andradiologist, there is a tendency to over scan, becausethe radiologist does not want to miss an importantfinding or to reschedule the patient for additionalscanning.CT dose data in this article were limited to fiveuniversity hospitals but showed substantial variationin doses across institutions. The authors suspect thatresults would be even more variable if hospitals ofMinistry of Public Health and private hospitals wereincluded in this survey. This implies need foroptimization to ensure that patients are given only thedose required for obtaining image of diagnostic qualityand no more.CT parameter settings in Thailand are usuallyperformed by specialists trained from CT vendors withthe acceptance of image quality by radiologists as aforemost consideration. General radiologists may havelimited knowledge regarding radiation dosecalculation. A national survey of the condition of theCT scanners and patient dose data by the authorizedagency (Department of Medical Sciences, Ministryof Public Health) is needed. Medical physicists indiagnostic radiology are not readily available, even insome university hospitals. Radiology professionalorganizations, such as the Royal College ofRadiologists, Society of Medical Physicists, and Societyof Radiological Technologists, should take part incontinuing educational courses and help to standardizeCT dose throughout the country as well as assurequality of the machines. Above all, the inappropriateutilization of CT for diagnosis that can be arrived byother methods must be discouraged.ConclusionCT scanning provides a great benefit in medicinebut it also becomes the major source of X-ray exposure.Radiation doses from a CT scan are much higher thanmost conventional radiographic procedures. This raiseconcerns about the carcinogenic potentials. Therefore,we encourage every CT unit to adhere to theInternational Guidelines of CT dose parameterreferences. It is comforting to learn that the radiationdoses of CT scan procedures from some universityhospitals in Thailand are within acceptable standardranges. We encourage the development of amechanism in every CT unit to ensure that thejustification for utilization of CT scans is required andmonitored.The authors have no conflict of interest to report.