From Volume 44, Issue 2, February 2017 | Pages 146-150
Hand-held dental X-ray equipment is increasingly being purchased for use in general dental practice. The aim of this paper is to update the practitioner with recently published recommendations on the requirements for hand-held devices. The article discusses the concerns often raised with the use of hand-held equipment including safety issues for the operator and the patient.
Hand-held X-ray devices are becoming increasingly used in general dental practice. In the UK, one manufacturer has reported that they sold 385 units, with the majority being to dentists, with a smaller number being used for veterinary, forensic and industrial applications.1 The same manufacturer states that the total number of worldwide sales is approaching 20 000 units.1
Hand-held devices either resemble a gun and are held in one hand, or resemble a camera and are generally held with both hands. An example of each type is shown in Figures 1 and 2. The construction of the X-ray tube is similar to traditional intra-oral equipment. The most striking difference in the tubehead is a shield that is attached to the open-ended spacer cone. This is in place to protect the operator from backscatter.
Hand-held devices have the following potential advantages over traditional wall-mounted dental X-ray sets in the dental surgery:
Public Health England recently advised that any hand-held equipment used for clinical use should fulfil certain requirements,2 including the following:
However, there are four major concerns regarding the use of hand-held X-ray devices:
There have been a number of publications relating to operator safety.3,4,5,6,7 These papers conclude that the operator dose using these systems is similar to the doses an operator would receive if using traditional X-ray equipment. One paper showed that the measured doses received by operators was actually lower than that received using a wall-mounted system.4 However, another paper measured the backscatter received by the operator and concluded that, in order to keep the received whole body dose below the 20 mSv per annum limit set by the International Commission on Radiological Protection, the number of exposures an operator could undertake would be 210, which is around 4 exposures per week.8 In addition, the maximum number of exposures that can be taken to keep the dose to the lens of the eye below the new recommended dose limit set by the International Commission on Radiological Protection (ICRP) is 180 exposures per annum.8 It should be pointed out, however, that this particular unit did not have the recommended backscatter shield.
The annual dose limit for an unclassified worker is 6 mSv per annum. The HPE guidelines suggest setting an annual dose constraint of 0.25 mSv for hand-held devices. The HPE tested five devices and only three of the models tested complied with this dose constraint.2
It seems that, overall, the doses to the operator can be kept below the dose limits set by the ICRP as long as the technique used by the operator is good. The operator should always have the backscatter shield on the unit and it should be placed to within 1 cm of the end of the spacer cone. The X-ray unit should be kept horizontal to ensure that the whole body of the operator is protected by the shield during the exposure. This may require the technique to be modified slightly, particularly in the positioning of the patient's head. Examples of this are shown in Figures 3 and 4. Most radiographic views taken in general dental practice can be acquired with hand-held units. However, views such as the lower 90 degree occlusal view cannot be carried out because the shield interferes with the positioning of the spacer cone underneath the patient's chin.
If a hand-held unit is chosen that meets the requirements of both the 2001 guidance notes for dental practitioners and the HPE guidelines on the safe use of hand-held X-ray equipment, and it is used correctly, then there is no need for the operator to wear Personal Protective Equipment (PPE), such as a lead apron or thyroid shield.
When buying new X-ray equipment, a prior risk assessment should be carried out and a full discussion should be carried out with the Radiation Protection Adviser as to the suitability of the equipment. When purchasing equipment, it should be sourced from a reputable dealer. Unfortunately, it is possible to buy cheap imported hand-held equipment over the internet. One particular piece of equipment was tested by the Health Protection Agency and it was found that, if it was used with a high workload, potential doses could be up to 40 Sv (equivalent dose) to the hands and 30 mSv (effective dose) to the body.9 These are clearly above the dose limits set by the ICRP. One unit had been purchased by a UK dentist. The HPA subsequently issued a medical device alert on this piece of equipment.9
Ideally, when using a hand-held unit in a surgery, the whole surgery should be designated a controlled area. Only the patient and the operator should be inside the controlled area when the exposure button is pressed. Access to the room should be restricted by either locking access doors or asking another member of staff to guard the entrance to the room.
In order to restrict the dose to the patient, equipment should be chosen that complies with the 2001 guidance notes for dental practitioners wherever possible.10 Equipment that operates at a high keV (between 60–70 KeV) and has a constant potential output should be selected. There should be no less than 1.5 mm aluminium filtration for X-ray sets operating up to 70 KeV. In addition, a long focus to skin distance (fsd) is advised.
This produces a near parallel beam that reduces the volume of the patient irradiated, reducing effective dose, and it also improves image geometry. A unit with an fsd of at least 200 mm should be chosen. As already discussed, rectangular collimation should be used in combination with image receptor holders and beam aiming devices. Rectangular collimators should be designed so that the beam size does not exceed 40 mm x 50 mm and preferably should not exceed 35 mm x 45 mm.
Hand-held units are battery operated and the units can make at least 100 exposures before the need for recharging. However, when low on charge the output can fall by as much as 10%.11 It is therefore suggested that units are kept fully charged to ensure optimal output.
A fast image receptor should be used – either a digital receptor or F-speed film. This ensures that the exposure times and subsequent radiation dose is kept as low as possible.
To ensure consistent acceptable image quality, image receptor holders and beam aiming devices should always be used. As previously stated, the holder may need to be modified to ensure that the end of the spacer cone can be placed next to the skin surface and to ensure correct centring and angulation of the spacer cone. This ensures that the beam is perpendicular to both the tooth and image receptor.
As the unit is hand-held, there is a potential for movement of the unit during the exposure (particularly as the exposures can be longer than with wall-mounted units). Therefore, exposures of longer than one second should not be selected. However, the image quality of radiographs seems similar to that of conventional X-ray equipment,5 but the data to support this finding was not presented in the paper. One study tested three different devices used with four different image receptors. All the images were of acceptable quality but there were significant differences in image quality between the combinations of the X-ray devices and the sensor types studied.
As the units are portable, there is potential for the units to be stolen and used without authorization outside the surgery. For this reason, the unit should be stored in a locked cupboard. If the unit is stolen, then the use of a PIN to activate an exposure would ensure that the unit cannot be used.
In a position statement prepared by the European Academy of DentoMaxillofacial Radiology it is stated that these devices should only be used in specific situations where the use of wall-mounted installations are either not possible or impractical.12 The indications for use are:
Although the indications in general dental practice are limited, there has been an increase in the number of units purchased. Therefore, if a dentist is considering buying one of these units, he/she is directed to the recent Health Protection England document which provides invaluable advice.2
