Requests. Who requests a DXA scan? DXA. DXA Technology. Adequate Clinical Information

Transcription

1 Requests Define a protocol for validation and prioritisation of densitometry requests. Registered medical practitioners In writing Include adequate clinical information Unsuitable requests should be discussed with referring doctor. Who requests a DXA scan? GPs Orthopaedist Rheumatologists Oncologists Obs/Gyn Geriatricians Radiologists Gastroenterologists Adequate Clinical Information GENETICS/ FAMILY HX OF FRACTURE FEMALE > MALE POST MENOPAUSE LOW BODY MASS INDEX LOSS IN HEIGHT FRAGILITY FRACURES SMOKING/XS ALCOHOL IMMOBILITY MEDICATIONS: CORTICOSTEROIDS INFLAMMATORY BOWEL DISEASE HYPERPARATHYROIDISM ANOREXIA MEN WITH LOW LEVELS OF TESTOSTERONE DXA Gold-standard for BMD measurement Measures central skeletal sites: spine and hip May measure other sites: forearm Extensive epidemiologic data Validated in many clinical trials Widely available Low Radiation Dose Photons DXA Technology Detector (detects 2 tissue types - bone and soft tissue) Patient Very low radiation to patient. Little scatter radiation to radiographer. Collimator (pinhole for pencil beam, slit for fan beam) X-ray Source (produces 2 photon energies with different attenuation profiles) 1

2 Radiation in DEXA Ionizing Imaging Technique Too much is dangerous, must be limited Patients, staff and public are at risk. Adherence to License issued by the R.P.I.I is necessary Adherence to local radiological safety regulations is necessary ALARA (As Low As Reasonably Achievable) Local Rules for Bone Densitometry Local rules should be drawn up by radiation safety committee / licence holder. This will help ensure compliance with the RPII licence conditions. National Osteoporosis Society (NOS) provide guidelines on local rules for DEXA. These local rules should be reviewed regularly and updated. Local Rules for Bone Densitometry (NOS) Operators must never expose themselves in the X-ray X beam During a scan only the patient should be within the controlled area Local Rules for Bone Densitometry (NOS) The operators desk should be placed well outside the controlled area Equipment not in use must be switched off and locked If you become pregnant you must inform your employer / RSO. Hazards of Ionizing radiation Cancer induction by radiation Genetic effects of radiation Risks are greatest for the foetus Need to ensure radiation protection of both staff and patients Radiation Protection of staff Never irradiate yourself in the X-ray X beam Stay outside of the Controlled Area while the patient is being scanned Be aware that scattered radiation from the patient may be significant Position work station at least 2 m from the foot end of the scanning table If the room size is too small to allow adequate distance a lead screen should be employed 2

3 Radiation Protection of staff Wear a film badge on the side that the patient is being scanned Radiation doses received by staff should be within laid down limits An operator must declare their pregnancy to the RPO Radiation Protection of the patient Justify and validate all scan requests Operator must check patient ID and ask about pregnancy Perform scans in a safe manner while ensuring that dose is ALARA. Pregnancy Status The unborn child is at risk of ionizing radiation Radiation Protection in pregnancy is essential Pregnancy Status Protocol for women under 50 years Date of patients last menstrual period is checked Ask the patient if there is chance she might be pregnant Record this information in writing on the request form Explain to the patient that this examination involves a relatively small dose of radiation, and this could be harmful to her foetus if she were pregnant Pregnancy Status Protocol If LMP is not within the first ten days the scan should be postponed until the beginning of the next menstrual cycle However Referring doctor may waive the LMP rule in writing Referring doctor may justify the exposure when the benefits of scan outweigh radiation risks Duties of Staff Small number of highly trained operators Obtain optimum scans Operate to the departmental protocols Consistent patient positioning and scan analysis Perform routine QC Adequate training in ionizing radiation Participate in CPD Retain professional membership of an appropriate organization such as IOS and NOS 3

4 Patient Preparation Identify correct patient Date of birth Sex Race Weight Height Assess pregnancy status Obtain previous scans Remove all metal objects from areas of interest Clear explanation of scanning procedure Patient questionnaire Patient Questionnaire Identify potential risk factors for osteoporosis Details of current medication Detail of skeletal fracture history Identify recent Imaging examinations which may affect the result Identify any hip or spinal orthopaedic surgery/ prostheses Orthopaedic prostheses Contrast Media Identify Artifacts Identify prior to scanning Prevents repeats and unnecessary radiation Artifacts can be a major cause of error if undetected Artifacts External or anatomical Metal objects such as buttons and body jewellary Barium/ Contrast agent Prostheses Hickman Line Aortic Calcification Paget s s disease Patient may not always report previous surgery 4

5 Optimum Scanning Measure patients weight and height accurately Identify artefacts Record scan parameters Use standard protocols for consistency and comparability Use correct patient positioning and scan analysis Ensure dose is ALARA Patient Positioning Protocols Skeletal Sites to Measure Measure BMD at both the PA spine and hip in all patients Scan Acquisition Scan analysis Forearm Forearm BMD should be measured under the following circumstances: Hip and/or spine cannot be measured or interpreted Very obese patients (over the weight limit for DXA table) Good Positioning- Spine PA Straight spine in the center of the scanning field Equal amounts of tissue on either side of spine Knees flexed over 90 support pad Center 1.5cms below the anterior margins of the iliac crests in the midline ASIS equidistant from the tabletop 5

6 DXA LUMBAR SPINE Good positioning- proximal femur ASIS equidistant from the tabletop Whole leg rotated by 25 Leg abducted by 15 to separate ischium from lesser trochanter Center 5cm below the greater trochanter and in the midline of the femur Arms positioned away from areas of interest Positioning devices DXA HIPS Vertebral Fracture Assessment Densitometric spine imaging performed for the purpose of detecting vertebral fractures Indications for VFA When BMD measurement is low, performance of VFA should be considered. Clinical situations that may be associated with vertebral fractures include: Documented height loss of greater than 2 cm History of fracture after age 50 Commitment to long-term glucocorticoid therapy History and/or findings suggestive of vertebral fracture Good Positioning- LVA Use of lateral support to position spinous processes of vertebrae parallel to the table Patient lies on left side with spine resting against the support Knees bent, arms positioned above the head Position lower back over curved support Place pad between the knees 6

7 LVA LVA Advantages Assessment of vertebral fracture status Low dose (1/100 of radiographs) Visualisation of the whole spine in one view Short scan time Use of Further Imaging Overweight patients poor image resolution Mild fractures are suspected Limited visualisation of upper thoracic spine Large discrepancy in BMD between vertebrae AP Spine Analysis Individual vertebrae falsely elevated by artifact should be removed Include at least two vertebrae Label the vertebrae correctly Correctly position Intervertebral ROI boxes In elderly patients the spine scan may be of little value if there is extensive degenerative disease Bone edge markers and intervertebral markers may need adjusting Spine Analysis Extensive Degenerative Disease Remove Falsely elevated vertebrae 7

8 Hip Analysis Hip Analysis Use femoral neck or total proximal femur, whichever is lowest BMD may be measured bilaterally or at either hip Check that the leg has been rotated and abducted correctly Check correct position of ROI boxes Check that bone edge markers are correctly positioned SEVERE OSTEOARTHRITIS OF RIGHT HIP Interpretation Good Practice Use of relevant reference ranges Use of WHO guidelines Recommendations made on the lower of the measurements at spine and hip Independent risk factors for fracture Guidelines on management and follow-up Baseline DXA Report sent to Doctor includes: BMD in g/cm 2 for each site The skeletal sites The T-score T and/or Z-score Z where appropriate WHO criteria for diagnosis in postmenopausal females and in men age 50 and over Explanation of results Risk factors including previous fragility fractures Fracture risk Unexpected results, for example a very high score for one vertebra which is out of context Indications for another imaging modality Management and Follow up T-score/ Z-scoreZ Risk factors including previous nontraumatic fractures Fracture risk Evaluation for secondary causes of low BMD Necessary Treatment Recommendations for the timing and necessity of your next BMD study 8

9 Follow-up BMD Measurement Should only be done when the expected change in BMD equals or exceeds the least significant change (LSC) LSC is the magnitude of change which must be measured to be sure that the change is real, not simply a result of measurement error Follow-up Scans Points to remember Have previous scans available for review Consistent patient positioning Consistent scan analysis Use of same software and scan compare facility Consistent approach between different operators Regular scanning of phantoms Daily block phantom System calibration QC phantom Ensures that the DXA equipment is operating as precisely and accurately as possible QA in DXA QA in DXA Follow manufacturer s s recommended IQC protocol using the phantoms provided Standard protocols for positioning phantom, acquisition and scan analysis Inspect results and report faults Scanner Maintenance and Repair -use of preventative maintenance program Summary Compliance with referral guidelines Benefits of exam must outweigh radiation risks Careful consideration of appropriate technique Operators should ensure that no person is exposed to radiation more than is reasonably necessary Consideration of frequency of follow up scanning Radiation protection in pregnancy is essential Use common sense: time, distance, shielding Useful Information Royal college of Physicians, UK Osteoporosis International Journal 9

10 10