Radiation protection of medical staff performing DXA

» What is the typical staff dose from a DXA examination?

The dose to staff in DXA facilities is generally small. However, new developments in DXA imaging technology (fan beam, cone beam, C-arm configurations) can result in larger scattered exposure levels. In some examinations the operator may be present in the scanning room; thus the scattered radiation from the total annual patient workload must be considered when assessing occupational dose levels. The reported scatter dose rates at 1m from the central axis of the patient table range from few tenths of a µSv/h to 5 µSv/h, depending of the scanner model. From these values, recent calculations and measurements indicate that the annual dose for an average workload (20 patients/day) at 1m from the scanner will be between 0.1 and 1.5 mSv depending the model of the scanner. These figures assume that staff do not comfort or hold children during examinations, and that this is done by parents or other comforters/carers.

In practical terms, the operators’ desk should be positioned at least 1m away from a pencil beam, and at least 2m from a fan-beam system. Some older models, that are not now common, require a distance of 3.5 m. In the case of fan-beam and cone-beam configurations or if the distances above can not be accommodated, the use of protective screens may be considered. With these precautions it is probable that the operator dose will be in the lower range of acceptable occupational exposures.

» My office is located next door to the DXA scanning room, should I be concerned?

In a properly designed DXA facility with an adequate room size, the radiation levels in adjoining rooms will be at a level acceptable for members of the public. Typically no additional shielding is required in the walls. The exposure to the person next door depends on the workload, the type of DXA scanner, the distance from the table axis to the walls and their composition. In some cases, additional radiation shielding may be required if the distance from the table axis to adjacent wall is less than 1 m. If the walls of the scanner room are of solid construction (i.e. solid concrete or brick, not cavity blocks or partition walls) or the desk in the office next in next room is more than 2 m away from the DXA system, then it is likely that the dose is within acceptable levels. However, estimates of dose, based on measurements, should be made at the time of installation and commissioning. Where possible the advice of a Radiation Protection Expert should be obtained.

» Does the design of DXA equipment affect staff doses?


It has been shown that the scattered radiation from modern fan-beam and cone-beam systems is greater than that from older pencil-beam DXA systems. Scatter is reported in terms of predicted annual dose at 1 m from the table (for assumed workload). Newer C-arm design DXA scanners permit lateral X-ray exposures and this may also result in increased scattered radiation. Although the scattered radiation from all DXA systems is relatively small, it should not be disregarded. Fan-beam and cone-beam systems may require shielding if the operator has to be seated close to the table or if the walls are close to the table. 

» Is personal monitoring required while working in the DXA room?

This depends on the national regulations. In some countries it is required that all occupationally exposed workers, who normally work in a controlled area, should wear a dose-monitoring badge or other device for the purposes of monitoring their individual exposure. In some cases it may be more suitable to monitor the workplace. The occupational radiation exposure for the operator depends upon the type of scanner technology, the workload and the relative position of the workstation with respect to the patient table. For further information, see the IAEA International Basic Safety Standards recommendations on individual monitoring. 

» Should one undergo special training for operating a DXA scanner?

This depends on the national regulations. Although a DXA scan is a relatively low-dose diagnostic procedure, formal staff training in radiation protection may be required and is the subject of regulation in some countries. In addition one should obtain specific training (from the supplier or manufacturer) on the operation of particular DXA system in use. 

» Should the operator wear a lead apron while performing a DXA scan?


It is not necessary for the operator to be close to the DXA scanner during the examination. Studies have shown that controlled area  can usually be limited to within 1m from the table for pencil beam and 2m for fan beams. If these distances are  not practical - mobile screens or structural shielding may be required. Radiation protection can be achieved by having adequate distance between the operator and the patient or using a fixed / mobile lead-acrylic screens, or a combination of both. Regardless of shielding requirements, staff should adhere to good radiation protection practice by minimizing the time spent close to the DXA scanner and patient during exposures. If there is doubt, the advice of a radiation protection expert should be sought.

» Can pregnant staff continue to work in the DXA scanning room?

Female workers should inform their employer if they become pregnant. A pregnant staff member can continue working in a DXA scanning room as long as the foetal dose is kept below 1mGy for the term of the pregnancy. 

Read more:

  • LARKIN, A., SHEAHAN, N., GRAY, L., O’CONNOR, U., DOWLING, A., VANO, E., TORBICA, P., SALAT, D., SCHREINER, A., NEOFOTISTOU, V., MALONE, J.F., Commissioning and Quality Assurance of Dual Energy X-ray Absorptiometry (DEXA) systems, Rad. Prot. Dosim. 2008 (in press). 
  • NJEH, C.F., FUERST, T., HANS, D., BLEKE, G.M., GENANT, H.K., Radiation exposure in bone mineral assessment, Appl. Radiat. Isot. 50 (1999) 215-236. 
  • PATEL, R., BLAKE, G.M., BATCHELOR, S., FOGELMAN, I., Occupational dose to the radiographer in dual X-ray absorptiometry: A comparison of pencil-beam and fan-beam systems, Br. J. Radiol. 69 (1996) 539-543. 
  • SHEAHAN, N.F., DOWLING, A., O'REILLY, G., MALONE, J.F., Commissioning and quality assurance protocol for dual energy X-ray absorptiometry systems, Rad. Prot. Dosim. 117 (2005) 288-290. 
  • STEEL, S.A., BAKER, A.J., SAUNDERSON, J.R., An assessment of the radiation dose to patients and staff from a Lunar Expert-XL fan beam densitometer, Physiol. Meas. 19 (1998) 17–26.