Children
Children have higher radiation sensitivity than adults and have a longer life expectancy. Therefore, imaging techniques that do not use ionizing radiation should always be considered as an alternative. Increasing numbers of radiological examinations are being performed in infants and children. Millions of children undergo high dose procedures such as computed tomography and interventional procedures. A paediatric radiological procedure should be individually planned and projections should be limited to what is absolutely necessary for a diagnosis.
Radiography and fluoroscopy
- What X ray procedures contribute most to individual patient dose and collective population dose?
- Are there special technical considerations required to reduce patient exposure and maintain good image quality in paediatric radiography?
- How does the radiation dose in screen-film combination imaging compare to digital imaging in paediatric radiography?
- Can low dose fluoroscopic image replace conventional radiographic examinations?
- What are the typical dose levels in paediatric radiology?
- What are the most significant things I can do to reduce patient dose during fluoroscopic examinations?
- Are there situations in which I should consider reducing the number of radiographic projections?
- How should one deal with possible pregnancy in adolescent patients?
Computed tomography
- How do I reduce the dose in paediatric chest CT?
- How do I reduce dose in paediatric abdominal CT?
- What safety measures are recommended for persons supporting the child during CT examination?
1. What X ray procedures contribute most to individual patient dose and collective population dose?
CT and interventional procedures are high dose procedures in radiology and yield higher individual patient doses than other radiological procedures do. The patient dose in CT is an important issue for children as reports suggest that in some centres the exposure factors used for scanning children are the same as for adults. This problem is relatively lesser in interventional procedures as the machine, on the basis of the body thickness falling in the X ray beam, automatically adjusts factors in most modern equipment. CT scanning contributes most to collective dose from radiographic exposures due to the increasing use of this modality. It has been reported that 30% of adults and children have three or more CT scans [METTLER, F.A., et al., CT scanning: Patterns, use and dose, J. Radiol. Prot. 20 4 (2000) 353-359].
2. Are there special technical considerations required to reduce patient exposure and maintain good image quality in paediatric radiography?
The short answer is YES. Specific actions include the following:
- Anti-scatter grids are normally not required in paediatric radiography as the gain in image quality does not justify the increase in patient dose, except in children in their teens and when the body build is such as to increase scatter [BSS II.16(b).iii].
- Good image detail is achieved by maintaining a balance between the use of a small focal spot size and a short exposure time.
- High speed screen-film combinations should be used where possible to enable reduction in radiation exposure and exposure time as the reduced resolution obtained is comparatively insignificant for the majority of clinical indications [BSS II.16(b).ii].
- The use of Automatic Exposure Control (AEC) is generally not appropriate in children as the sensors (size and geometry) are normally designed for adult patients. Instead, exposure charts corresponding to radiographic technique, patient thickness in the X ray beam and presence or absence of anti-scatter grid are much safer and easier to use.
- The radiation beam should be limited using collimation [BSS II.16(b).iv].
- Shielding devices should be appropriately positioned to be efficient for protecting the tissues for which they are placed and to avoid unnecessary repeat examinations [BSS II.16(f)].
- Immobilization, when required, should be provided by specialized devices, if possible.
Further details are available in [EUR 16261].
3. How does the radiation dose in screen-film combination imaging compare to digital imaging in paediatric radiography?
In general, digital detectors offer the possibility of dose reduction in a similar way as is done in adult radiography. It should be emphasized that while with screen-film combinations overexposure may result in a non-diagnostic image, overexposure using digital detectors may not be as readily recognized as it may result in acceptable quality image. Increased dose in digital imaging can also be caused by re-exposure by technologists not being detected (in most systems currently available), ease and convenience with which images can be taken thus leading to covering a larger area of a patient's body or repeating the examination. Whereas it is possible to have dose reduction, many studies indicate that in actual practice, more so where optimization is lacking, there is increase in patient dose. Further details are available elsewhere on this Website and in [ICRP 93].
4. Can low dose fluoroscopic image replace conventional radiographic examinations?
The general answer is NO.
An image recorded on film with a high-speed cassette provides a permanent record that can cover the necessary area, e.g. leg, spine. However, when high image detail is not required, for example in follow-up examinations in patients with scoliosis, leg length discrepancy, a stored pulsed fluoroscopic image using last-image-hold may be satisfactory.
5. What are the typical dose levels in paediatric radiology?
Typical values of Entrance Surface Dose (ESD) per radiograph and Dose Area Product (DAP) for common paediatric fluoroscopy examinations are given in Table 1.
Table 1. Typical dose levels in paediatric radiology [NRPB-W14]
| Examination | Entrance surface dose (µGy) | ||||
|---|---|---|---|---|---|
| Age | |||||
| 0 | 1 | 5 | 10 | 15 | |
| Abdomen AP | 110 | 340 | 590 | 860 | 2010 |
| Chest PA/AP | 60 | 80 | 110 | 70 | 110 |
| Pelvis AP | 170 | 350 | 510 | 650 | 1300 |
| Skull AP | / | 600 | 1250 | / | / |
| Skull LAT | / | 340 | 580 | / | / |
| Dose area product (mGy.cm2) | |||||
| MCU | 430 | 810 | 940 | 1640 | 3410 |
| Barium meal | 760 | 1610 | 1620 | 3190 | 5670 |
| Barium swallow | 560 | 1150 | 1010 | 2400 | 3170 |
6. What are the most significant things I can do to reduce patient dose during fluoroscopic examinations?
Many actions are similar to those recommended in adult procedures:
- The patient should be positioned as close as possible to the image intensifier.
- The X ray tube should be as far away as possible from the patient table in order to avoid excessive skin dose.
- The lowest frame rate acceptable and last-image-hold facility should be used. Further details are available.
- Some centres prefer to set a 'floor' (a kVp) below which the system will not go, such as 70 kVp for paediatric patients and 80 kVp for adults.
- Additional copper filtration also reduces patient dose.
7. Are there situations in which I should consider reducing the number of radiographic projections?
The short answer is YES.
When performing radiographs of long bones in children the opposite limb should be imaged if needed by the radiologist and only limited views used. In chest radiographic examination a lateral projection may not be required routinely. When a follow-up examination is justified the number of projections should be restricted to evaluate previous findings [BSS II.16(b).i]. Lumbar spine for follow-up and sometimes for regular examination is an example with too many projections like AP, lateral, obliques, and L5-S1 spot film.
8. How should one deal with possible pregnancy in adolescent patients?
The necessary information on possible pregnancy should be obtained from the patient herself. Further details are available. In female children who are menstruating and are referred for high dose procedures such as CT abdomen or interventional examination, the possibility of pregnancy should be considered.
9. How do I reduce the dose in paediatric chest CT?
The recommended actions are:
- Image quality in CT is generally more than what is required for confident diagnosis. Awareness on this can help in significant reduction in patient dose.
- Radiologists and physicians should be aware that images with low noise, even if they do not look very crisp, may provide the diagnostic information.
- mAs reduction at defined kVp has been used with success by many centres and is the most efficient method of dose management in children as also in adults. There is lack of consensus on kVp reduction in CT examination.
- Many authors suggest using 100–200 mAs settings for high resolution chest CT in children. However, reliable diagnostic studies can be obtained using much lower mAs. In cooperative children who are able to breath-hold as low as 34 mAs can be used and in non-cooperative children 50 mAs [LUCAYA, J., et al., Low-dose high resolution CT of the chest in children and young adults: Dose, cooperation, artifact incidence and image quality, Am. J. Roentgenol. 175 4 (2000) 985-992].
- Whenever radiosensitive tissues such as breast and thyroid fall within the exposed area, they should be shielded. Breast-anlage (primordium or the first rudiment of the breast, the underdeveloped tissue) protection using for example 2 mm thick bismuth coated latex shielding reduces the dose to the breast-anlage by approximately 40%.
- Recent technology developments include automatic tube current modulation where the tube current is adjusted according to thickness and density of tissues to maintain a constant level of image noise.
10. How do I reduce dose in paediatric abdominal CT?
Strategies should include obtaining only necessary CT examinations. MRI and US should take priority. If possible, the examination should be tailored to answer the specific question asked by the referring clinician, for example pelvic scanning is not always necessary when an abdominal scan is requested and it maybe possible to curtail follow-up CT exams to a specific organ. In addition, imaging parameters such as kVp and mAs need to be adjusted for patient size. Size-based tables for abdominal multidetector CT and body CT angiography in children are available [FRUSH, D.P., Review of radiation issues for computed tomography, Seminars in Ultrasound, CT and MRI, 25 1 (2004) 17-24]. In one study, children were classified by colours based on weight and this was shown to significantly reduce scanning errors in settings for paediatric multi-detector CT [FRUSH, D.P., et al., Improved paediatric multi-detector CT using a size-based color-coded format, Am. J. Roentgenol. 178 3 (2002) 721-726].
Recent technology developments include automatic tube current modulation where the tube current is adjusted according to thickness and density of tissues to maintain a constant level of image noise.
Finally, the use of multiphase scanning should be curtailed as much as possible.
11. What safety measures are recommended for persons supporting the child during CT examination?
As a general principle, the BSS require that parents or family members rather than staff in the radiology facility, should support the child during any radiological examination. And, when parents or family members support the child during the examination, they should be provided with appropriate shielding [BSSII.27].
References
- EUROPEAN COMMISSION, European Guidelines on Quality Criteria for Diagnostic Radiographic Images in Paediatrics, EUR-16261, Luxembourg (1996).
- INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Managing Patient Dose in Digital Radiology, ICRP Publication 93, Pergamon Press, Oxford and New York (2004).
- NATIONAL RADIOLOGICAL PROTECTION BOARD, Doses to Patient from Medical X Ray Examinations in the UK: 2000 review, NRPB-W14, Chilton (2002).
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