Patient exposure trends and problems in implementing ALARA Barry Wall Medical Exposure Department Radiation Protection Division Health Protection Agency Chilton, UK

Uses of radiation in medicine Medical radiology X-ray imaging for diagnosis X-ray imaging to guide therapeutic interventions Radionuclide imaging (nuclear medicine) Radiotherapy Together  99% of man-made population dose

Medical X-ray Imaging Radiography Effective dose Cancer risk 10 µSv <1 in a million Radiation doses & risks increasing Fluoroscopy Computed Tomography 20 mSv ~ 1 in 1000

X-ray examinations in 4 dose bands Effective dose Typical % of total % of total range (mSv) x-ray exams no. of exams collective dose <0.02 Radiography of 73 1 chest, limbs, teeth 0.02 - 0.2 Radiography of 5 1 head, neck, joints 0.2 - 2.0 Radiography of spine, 16 20 abdomen, pelvis 2 - 20 CT, angiography, 6 78 contrast studies of GI, biliary & urinary tracts

Course Introduction (RADSAFE) Typical Effective Doses from X-ray Procedures Chest Skull Abdomen Pelvis / hip Lumbar spine IVU (urinary tract) Ba meal (stomach) Ba enema (colon) CT body Angiography Interventional Thoracic spine CT head 5 10 15 20 Effective dose, mSv Typical values of E per procedure for developed countries Mean values range from 0.1 to 20 mSv, but significant variations in practice for given type of exams between different x-ray departments and individual patients Quite low doses for many common exams: fractions of a mSv for chest, head, limbs and joints 1-2 mSv for exams of the abdomen, pelvis, lumbar or thoracic spine Larger doses for urography and barium meal (4 mSv), barium enema (6 mSv) CT - 2 mSv for head, but about 10 for body Complex angiography and intenventional procedures typically between and 10 and 20 mSv Highest dose band

Conventional Radiography Course Introduction (RADSAFE) Conventional Radiography Images of bones obtained on film sandwiched between intensifying screens in cassette below patient couch

Course Introduction (RADSAFE) Conventional Fluoroscopy Ba study of colon Fluoroscopy provides real-time images, move collimated x-ray beam and electronic image intensifier, images on TV monitor Used for example in barium studies of gut, meals and enemas where barium introduced into stomach or colon to enhance contrast Image intensifier

Course Introduction (RADSAFE) Single slice axial CT

Recent developments in medical imaging Digital radiography Storage phosphors or flat-panel detectors  static digital images Amorphous selenium coating over TFT matrix Digital fluoroscopy Image intensifier or flat panel detector  moving digital images and DSA

Recent developments in medical imaging Multi-slice helical CT Up to 64 rows of detectors across beam 0.5 s rotation time  3D images with 0.6 mm isotropic spatial resolution

Image from 64 slice CT scanner

Recent developments in medical imaging Increasing use of fluoroscopy-guided key-hole surgery by non-radiology clinicians (eg. cardiologists) Prolonged fluoroscopy with static x-ray beam can produce tissue reactions

Patient Dose Measurement Methods Radiography Fluoroscopy CT Entrance surface dose (ESD) Direct measurements can only be made in x-ray beam outside the patient Fluoroscopy Dose-area product (DAP) CT CT dose index (CTDI) 38507, 29033, 29037

Calculation of organ doses Simulate x-ray exams on mathematical phantoms and follow tracks of millions of x-ray photons through phantom Calculate energy deposited in each organ & external dosemeter to derive coefficients relating organ doses to the measurable dose quantities (ESD, DAP or CTDI) Conventional X-ray exams CT examinations Family of phantoms Baby 1y 5y 10y 15y Adult

1983 NRPB Patient Dose Survey Abdomen AP Frequency Entrance surface dose per film, mGy 10 15 30 45 60 20 40 Abdomen AP Best hospital Worst hospital 22834

Radiation protection principles for medical exposures Justification Optimisation But no dose limits

Optimisation of medical exposures X-ray equipment and techniques should be selected to ensure that patient exposures are ALARA consistent with obtaining the required diagnostic information How?

DRLs - the first step to ALARA Patient exposures cannot be reduced indefinitely without impact on image quality Radiologists subjectively assess the adequacy of their images every time they report on them but they cannot intuitively assess the patient dose (particularly with modern digital systems) DRLs provide a means for alerting radiologists when their patient doses become unusually high

DRLs - the first step to ALARA Concept of DRLs recognised in: - ICRP Publications 60 (1991) & 73 (1996) - IAEA BSS (1994) - EC Medical Exposure Directive (1997) DRLs usually set at 3rd quartile of dose distributions seen in national patient dose surveys Hospitals with mean doses > DRL should investigate why and take corrective action, if not clinically justified DRLs are ‘investigation levels’ triggering further optimisation where most urgently needed.

DRLs - the first step to ALARA On exceeding DRL, the subsequent investigation will involve detailed analysis of existing routine performance tests on the x-ray equipment (that include simple image quality checks) [e.g. IPEM Report 91] and reference to international guidance on good imaging techniques:- e.g. in European Guidelines on Quality Criteria for adult and paediatric radiography and CT

Trends in UK DRLs for radiographs (1985 - 2000) Course Introduction (RADSAFE) Trends in UK DRLs for radiographs (1985 - 2000) Radiograph Entrance Surface Dose (mGy) . 1985 1995 2000 Skull AP/PA 5 4 3 Skull LAT 3 2 1.5 Chest PA 0.3 0.2 0.2 Chest LAT 1.5 0.7 1 Thoracic spine AP 7 5 3.5 Thoracic spine LAT 20 16 10 Lumbar spine AP 10 7 6 Lumbar spine LAT 30 20 14 Lumbar spine LSJ 40 35 27 Abdomen AP 10 7 6 Pelvis AP 10 5 4 Average 2000/1985 = 0.56

Trends in UK DRLs for exams (1985 - 2000) Course Introduction (RADSAFE) Trends in UK DRLs for exams (1985 - 2000) Examination Dose-area product, Gy cm2 ___________________________________ 1985 1995 2000 IVU (urinary system) 40 25 16 Ba meal (stomach) 25 17 13 Ba enema (colon) 60 35 31 2000 1985 Average = 0.48

Trends in doses for CT (UK 1991 - 2003) 1991 (SSCT) 2003 (MSCT) ------------------------ -------------------------- CT exam DLP E DLP E (mGy cm) (mSv) (mGy cm) (mSv) Head * 1050 2 930 1.5 Chest * 650 8 580 5.8 Abdomen * 780 10 470 5.3 Pelvis 570 10 - - Abdo+pelvis - - 560 7.1 Chest+abdo+pelvis - - 940 9.9 * 2003/1991 = 0.8 - 0.5

Future problems in implementing ALARA Although doses are coming down for ‘old routine’ CT exams scanning speeds have increased and whole trunk scans (with higher doses) are becoming the ‘new routine’. Only radiologists can decide whether these increasing patient doses are ‘reasonable’ in relation to the extra diagnostic information obtained. BUT they need to be reminded regularly to consider if the doses are ALARA - through the use of DRLs. The major problems arise in trying to keep abreast of all these rapid developments in medical imaging and their impact on patient exposures, so that appropriate DRLs can be established to implement ALARA - ASAP