Unable to process the form. Check for errors and try again. Thank you for updating your details. Log In. Sign Up. Become a Gold Supporter and see no ads. Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. View revision history Report problem with Article. Citation, DOI and article data. Morgan, M. Similar differences were also observed with the body filter, for which data ranged from 1.
Left: Data obtained with head filter and cm-diameter acrylic dosimetry phantom. Right: Data obtained with body filter and cm-diameter acrylic dosimetry phantom. Table 1 lists the locations of radiosensitive organs, which explains the observed peaks. The vendor was GE Medical Systems.
Solid circles solid lines are head scans, and open circles dashed lines are cervical spine scans, with these scans defined in Table 1. Lines are least-square fits to a second-order polynomial. Solid circles solid line are chest scans, open circles dashed lines are abdominal scans, and triangles dotted lines are pelvic scans, with these scans defined in Table 1.
Each line is obtained from a least-square fit. The ImpactDose coefficient for cervical spine examinations All scans were performed at kV in a male patient by using the scans defined in Table 1. The scanner model was Sensation 16 Siemens.
In comparison to conventional radiography, CT is a high-dose imaging modality, although doses are generally well below the threshold dose for the induction of deterministic effects 18 , As a result, the risk from CT radiation is that of carcinogenesis and the induction of genetic effects, which is best quantified by the ED 20 , The recent advent of multidetector CT has resulted in an increasing utilization of this imaging modality, with an estimated 57 million CT examinations performed in the United States in CT imaging is now the dominant contributor to the population dose from medical x-rays, where the latter is the major source of radiation exposure from man-made sources.
A major benefit of generating the ED associated with a CT examination is the ability to directly compare patient doses ie, risks at CT with those at other diagnostic procedures that involve ionizing radiation. The ED of a CT scan can be directly compared with corresponding ED values of radiography and fluoroscopy, as well as nuclear medicine 24 , A chest CT examination, for example, has an ED between 5 and 10 mSv, whereas a standard two-view chest radiographic examination has an ED of approximately 0.
Data for the head and cervical spine examinations were not commensurate with those for chest, abdominal, and pelvic examinations. The former have very low ED values, as well as higher CTDI vol because these are obtained in head phantoms 16 cm in diameter.
Body EDs are generally five times higher than head EDs, but the CTDI vol values in cm-diameter acrylic cylinders are only about half of those obtained in cm-diameter cylinders.
Our study results show that a short 2-cm scan length will result in markedly different values of patient ED, depending on the z-axis position of the x-ray beam. For narrow scans on the order of 2 cm, differences in anatomic location alone can result in differences in ED of up to a factor of These variations in patient ED are directly related to the locations of radiosensitive organs and tissues, which are predominantly located in the body.
In practice, however, few clinical scans have such narrow scan lengths. Similar findings were obtained for scanners that spanned 25 years from one manufacturer. The likely reason for this finding is that differences in scanner design such as geometry, filtration, and beam-shaping filter, which affect the x-ray tube output, will have similar effects on both ED and CTDI vol. The reason for this difference is that the head does not contain any substantially radiosensitive organs, whereas the body region does eg, lung, colon, stomach, red bone marrow.
Increasing the x-ray tube voltage also increases the x-ray beam penetration and increases the relative doses to the organs that make the largest contribution to the patient ED.
Our data show that when body CT scans are performed at values that differ from the standard kV, a correction needs to be made to account for the selected x-ray tube voltage. Variations in the pitch ratio are likely to affect ED and DLP in a similar manner, provided that the CT scan covers a relatively large region. Pitch could be important for short scan lengths, however, because the absorbed dose could depend on the location of the x-ray tube relative to the location of any small radiosensitive organs.
All patient and phantom doses were obtained by using software and were not independently verified with any radiation dose measurements. All three software packages use idealized mathematical anthropomorphic phantoms, which will differ from any real patient Accordingly, the EDs generated in this work relate to a nominal reference patient, with specific sizes and locations of each organ and tissue. Of greater importance is that EDs are only valid for a reference-sized individual who weighs approximately 70 kg.
This article describes a method of providing CT users with a practical and reliable estimate of adult patient EDs by using the DLP displayed on the CT console at the end of any given examination. Knowledge of patient EDs will allow all stakeholders in CT, including patients, to better understand the amount of radiation a patient receives in a given diagnostic test and will be a valuable tool for minimizing patient doses from this imaging modality 4 , ED from CT could be compared with a range of benchmark EDs, including natural background radiation cosmic, terrestrial, and internal of 1 mSv per year and the average radon exposure in the United States of 2 mSv per year Diagnostic tests may also be compared with regulatory dose limits for occupational exposure 50 mSv per year , as well as for members of the public 1 mSv per year.
Converting EDs to radiation risk and detriment estimates would also be possible but must be performed with care 31 — The data permit operators to convert the DLP value generated by most commercial CT scanners into a corresponding ED, assuming a normal-sized adult patient. The data also permit operators to compare patient EDs of CT with those of other x-ray based imaging examinations, as well as with benchmark values, including natural background radiation and regulatory dose limits.
We thank Paul C. Authors stated no financial relationship to disclose. Author contributions: Guarantors of integrity of entire study, W. National Center for Biotechnology Information , U. Ogden , PhD, and Mohammad R. Khorasani , MD. Find articles by Walter Huda. Kent M. Find articles by Kent M. Mohammad R. Find articles by Mohammad R. Author information Copyright and License information Disclaimer. To convert from equivalent dose to effective dose we multiply the dose to each organ by a weighting factor associated with that organ.
These weighting factors are defined by the ICRP and account for the different radiation sensitivities of different tissue types.
The effective dose, again we take the equivalent dose and we weight all the different organs based on the radiation dose each organ received. If we want to do this properly, we have to either measurements in phantoms, which are anthropomorphic ie. Or you have to do Monte Carlo simulations where you simulate the x-rays passing through the anatomy. Or some combination of phantom measurements and computer simulations of the radiation dose.
All this gives you Effective Dose mSv numbers where we can figure out how much of the brain, how much of the gonads, and how much of the other organs are receiving radiation dose in a very specific manner. However, these methods are also a very complex as we need to model each patient. Luckily for us there is a simplified method to arrive at approximate estimates of the Effective Dose mSv.
We first need to define the Dose Length Product as this will be used in the approximate Effective Dose mSv calculations. As discussed above CTDI is a measure of the absorbed radiation dose, the absorbed dose for a given size phantom. Then we need another method to take into account how long the scan was, namely what is the scan length along the SI direction ie.
Since the CTDI is normalized to some given length across this direction we need to multiply by the scan length to calculate the dose length product DLP. We can think about two scans which have the same CTDI but which cover different ranges of the patient anatomy. It is clear that we would like to treat these scans differently when considering the radiation dose to the patient.
This is why we need to use the DLP and we can keep track of the scan range dependence by just multiplying by the scan length, as mentioned above. You can see that this figure looks similar to the one presented above for Radiation Dose in x-ray Radiology.
However, in this figure we present the approximate method. The input for this approximate method is the CTDI measured in a representative phantom, 16cm for adult heads and 32 cm for adult bodies. That conversion factor is dependent on the body part s being scanned, and the patient age.
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