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Intro || Types || Production || Interaction || Attenuation || Biological Effects || Gas Detectors || Scintillation Counters || Protection Principles || Units || Practical || DEXA Theory || Dosimetry || References
This page contains the following sections:
Introduction
Effective dose is the sum of the weighted equivalent doses in all tissues and organs of the body:
where:
WT: weighting factor for the tissue or organ, T
HT: equivalent dose in tissue or organ, T
expressed as:
where:
WR: weighting factor for radiation, R
DTR: absorbed dose averaged over tissue, T due to radiation, R
Therefore, equivalent dose is the absorbed dose averaged over a tissue or organ and weighted for the radiation quality.
WR for X-rays = 1
Therefore, for X-rays, the absorbed dose is numerically equal to the equivalent dose.
Some WT values:
|
Tissue/Organ |
Weighting Factor, WT |
|
Gonads Bone Marrow Lung Breast Liver Thyroid Skin Bone Surface |
0.2 0.12 0.12 0.05 0.05 0.05 0.01 0.01 |
Patient Doses in Bone Mineral Densitometry
[Huda W and Morin RL, 1996, British Journal of Radiology, 69, 422-425]
|
BMD Technique |
Radiation Dose (µSv) |
Comments |
|
DEXA SEQCT DEQCT Radiograph |
~2.5* ~300 ~1,000 ~100 |
single PA scan scout + 3 CT slices scout + 3 CT slices single collimated view |
* range: 0.5-4.5 µSv
Representative Radiation Doses in Diagnostic Radiology
|
Examination |
Range (µSv) |
|
Chest Skull Pelvis Abdomen Lumbar Spine Ba Meal IVU Head CT scan Body CT scan Nuclear Medicine |
10-50 100-200 700-1,400 600-1,700 1,300-2,700 1,900-4,800 2,500-5,100 2.000-4,000 5.000-15,000 2,000-10,000 |
Doses Expressed as an Equivalent Time of Natural Background (2 mSv/y)
|
Examination |
Equivalent Time |
|
PA Chest Pelvis Mammography Lumbar Spine Ba Meal CT Head scan Bone scan (99mTc) |
3 days 10 weeks 10 weeks 23 weeks 1.3 years 1.4 years 2.2 years |
Comparison of Two Generations of DEXA Scanner
[Njeh CF, Apple K, Temperton DH and Boivin CM, 1996. Radiological assessment of a new bone densitometer - the Lunar EXPERT. British Journal of Radiology, 69, 335-340]
|
Model |
Scan Width (mm) |
Spine Effective Dose (µSv) |
Femur Effective Dose (µSv) |
|
Lunar DPX-L Lunar EXPERT |
- 180 150 120 |
0.21 74.7 44.7 30.9 |
0.15 44.9 34.1 32.0 |
Scatter Dose Rates
|
Model |
Scan Width (mm) |
Distance (m) |
Scatter Dose (µSv/h) |
|
Lunar DPX-L
Lunar EXPERT |
-
180 180 180 150 120 |
0.5 1 0.5 1 2 1 1 |
<2 <1 240 64 18 46 42 |
Conclusion:
Operator 1 m from beam - no protective screen and no additional protective devices for the public in adjoining areas is necessary
Operator should be >3.5 m from beam or behind a protective screen, dependent on workload
Intro || Types || Production || Interaction || Attenuation || Biological Effects || Gas Detectors || Scintillation Counters || Protection Principles || Units || Practical || DEXA Theory || Dosimetry || References
Last Updated: 24 Jan 98
