GB/T 16137-2021Methods for estimation of examinee's organ doses in X-ray diagnosis (English PDF)

4.1 General X-ray photography

4.1.1 Organ dose calculation formula The organ dose is calculated according to formula (1). DT=CT·Ka,e (1) Where. DT

--- the absorbed dose of tissues or organs, in milligrays (mGy); CT

---organ dose conversion coefficient, the unit is milligray per gray (mGy/Gy); Ka,e-the kerma kinetic energy of the air incident on the body surface, in gray (Gy).

4.1.2 Obtaining the kerma kinetic energy of the air on the surface of the incident body

4.1.2.1 The actual measurement results of the kerma (Ka,

e) of the incident surface air should be used first.

4.1.2.2 If there is no actual measurement result of the air kerma of the body surface, the PKA value of the area product of the air kerma can be used to estimate according to formula (2) Calculate Ka,e. Ka,e= PKA W·L · SID FSD ·BSF (2) Where. Ka,e

--- the kerma kinetic energy of the incident surface air, in gray (Gy); PKA

---The product of air kerma kinetic energy area, in gray square centimeters (Gy cm2); W

--- the width of the irradiation field, in centimeters (cm); L

--- the length of the irradiation field, in centimeters (cm); SID

--- the distance from the focus to the receiver, in centimeters (cm); FSD

---focus distance, in centimeters (cm); BSF

---Backscattering factor (see Appendix A).

4.1.3 Organ dose conversion factor

4.1.3.1 Adult organ dose conversion factor. Tables C.1 to C.15 in Appendix C show six common body positions for adult X-ray photography. Test the dose conversion factor of each tissue or organ.

4.1.3.2 Children's organ dose conversion factor. Table C.16~Table C.30 in Appendix C show two common positions for X-ray photography of 5-year-old and The dose conversion coefficient of each tissue or organ in a 10-year-old child.

4.1.3.3 When estimating the organ dose of a particular subject, if the size and quality of the subject are similar to those listed in Appendix C, Similarly, the corresponding organ dose conversion coefficients in Table C.1~Table C.30 can be used directly. The dose of irradiation field changes to the exposed organs in the irradiation field The impact is negligible, but it has a greater impact on the exposed organs in the field. For the same posture photography, the actual FSD used is the same as in Appendix C The difference in FSD listed has relatively little effect on the dose of organs in the irradiation field.

4.2 X-ray fluoroscopy

4.2.1 The calculation of the subject's organ dose caused by X-ray fluoroscopy can refer to formula (1).

4.2.2 The method of obtaining the kerma kinetic energy of the incident surface air by X-ray fluoroscopy can refer to 4.1.2.

4.2.3 The organ dose conversion coefficients of adult men and women undergoing X-ray fluoroscopy in different positions are as follows:

a) For the organ dose conversion coefficients of adult men and women undergoing esophageal fluoroscopy, see Table D.1 to Table D.6 in Appendix D;

b) Refer to Table D.7 and Table D.8 of Appendix D for the organ dose conversion coefficients of adult men and women undergoing gastric fluoroscopy;

c) For the typical values of the organ dose conversion coefficients for adult men and women receiving cardiovascular angiography, see Appendix D, Table D.9.

4.3 Mammography

4.3.1 Organ dose calculation formula The average breast dose is calculated according to formula (4). DG=CG·Ka,i (4) Where. DG

--- average breast dose, in milligrays (mGy); CG

---The average dose conversion coefficient of different targets/filters and different proportions of glands, in milligray per milligray (mGy/mGy); Ka,i-the kerma kinetic energy of incident air, in milligray (mGy).

4.3.2 Obtaining the kerma kinetic energy of incident air

4.3.2.1 The actual measurement results of the kerma (Ka,

i) of incident air without the subject or phantom should be used first.

4.3.2.2 If the measured data of the kerma (Ka,

e) of the air on the surface of the incident body measured in the presence of the subject or the phantom is used, it can be The backscatter factor BSFG of mammography is used to estimate Ka,i according to formula (5). Ka,i= Ka,e BSFG (5) Where. Ka,i

--- kerma kinetic energy of incident air, in milligrays (mGy); Ka,e

--- kerma kinetic energy of incident surface air, in milligrays (mGy); BSFG

---The backscatter factor for mammography (see Table E.7 in Appendix E).

4.3.3 Breast dose conversion factor Refer to Table E.1~Table E.6 of Appendix E for the average breast dose conversion coefficients of different target/filtered and different proportions of glands.

4.4 Computer Tomography (CT)

4.4.1 Organ dose calculation formula The organ dose is calculated according to formula (6). DT=CCT·nCVOL·PIt (6) Where. DT

--- the absorbed dose of tissues or organs, in milligrays (mGy); CCT

---CT-induced organ dose conversion coefficient of the subject, the unit is milligray per milligray (mGy/mGy); nCVOL

---Volume CT air kernal energy index in milliampere second, in milligray per milliampere second [mGy/(mA·s)]; PIt

---The milliampere second value of the CT tube rotating one circle, the unit is milliampere second (mA·s).

4.4.2 Obtaining volumetric CT air kerma kinetic energy index

4.4.2.1 It is preferred to read directly from the radiation dose structured report (RDSR) of the CT system.

4.4.2.2 If it cannot be read, the weighted CT dose index CTDIW (equivalent to CT Air kerma kinetic energy index CW), and then use formula (7) to calculate CVOL. CVOL= CW·N·T Deltad (7) Where. CVOL

---Volume CT air kernal kinetic energy index, the unit is milligray (mGy); CW

---CT air kerma kinetic energy index, the unit is milligray (mGy); N

---The number of slices generated in one scan; T

---CT scan thickness, in millimeters (mm); Deltad

---The distance that the CT tube rotates once the diagnostic bed moves, in millimeters (mm).

4.4.3 Organ dose conversion factor

4.4.3.1 Refer to Appendix F Table F.1 for the conversion factor of adult reference human organ dose.

4.4.3.2 For the organ dose conversion coefficients of children of different ages, see Table F.2~Table F.4 in Appendix F.

4.4.3.3 When estimating the organ dose of a specific subject, the manufacturer and model of the CT device used are the same as those listed in Appendix F. When the models are the same, the corresponding organ dose conversion coefficients in Table F.1 to Table F.4 can be used directly. When the manufacturer or model is different, the The organ dose conversion factor will have a greater degree of uncertainty.

5.1 Parameter selection

5.1.1 Ray source item. X-ray energy spectrum can use EGSnrc, FLUKA, GEANT, MCNPX, MCNPX. Software such as 1) is obtained by Monte Carlo (MC) simulation calculation, and can also be obtained with the help of X-ray energy spectroscopy that has been publicly released by relevant research institutions at home and abroad. Into software (such as XCOMP5R). The key factors affecting the energy spectrum mainly include the tube voltage and the overall filter setting. 1) The above commercial software is an example of software that can be used to simulate and calculate the X-ray energy spectrum. This information is given for the convenience of users of this document, and Does not indicate an endorsement of these software. If other equivalent software has the same effect, you can use these equivalent software.

5.1.2 Human body model. commonly used voxel (Voxel) model, because of its more detailed description of organs. Non-uniformity based on surface definition can also be used The rational B-spline curve (NURBS) model, which can customize the size and composition of each organ according to the individual, such as adjustable height And body weight, can construct different breast size, shape, ratio of breast to adipose tissue, etc.

5.1.3 Irradiation situation. mainly refers to the relative geometric position of the ray source and the human body model and the geometric size of the irradiation field.

5.2 Calculation method Define the radiation source items and the subject's human body model (age, body type, etc.) of the various X-ray diagnosis in 5.1, according to the specific exposure situation Carry out MC simulation calculation, respectively count the energy deposited in the organ or tissue of interest divided by the mass of the organ or tissue, and calculate The average organ dose can also be calculated directly (DT, MC). By increasing the number of particles (photons) calculated by simulation, Reduce the error of MC simulation calculation. The results of the MC simulation output are normalized to each emitted source particle (photon), and the same situation should be used. The ratio of the actual measured value (VM) and the simulated calculated value (VMC) of a specific physical quantity is converted, and the calculation is shown in formula (8). DT=DT,MC· VM VMC (8) Where. DT

--- the estimated value of the absorbed dose of the organ or tissue; DT, MC-MC simulation calculation value of absorbed dose of organ or tissue; VM

--- the measured value of a specific physical quantity; VMC

--- The simulated calculated value of a specific physical quantity.

5.3 Conversion factor When the MC simulation calculation is carried out according to the methods described in

5.1 and 5.2, the corresponding incident air comma can be obtained at the same time in a simulation Energy and organ dose, the ratio of the two is the organ dose conversion coefficient. However, the conversion factor is only for a specific irradiation situation, if the irradiation situation (Including the equipment source item, the age and size of the subject) changes, the MC method can be used to recalculate the organ dose under different exposure situations Conversion factor.

6.1 The effective dose of ordinary X-ray radiography subjects

6.1.1 Effective dose calculation formula The effective dose is calculated according to formula (9). E=CE·Ka,e (9) Where. E

--- effective dose, the unit is millisievert (mSv); CE

--- effective dose conversion factor, in millisievert per gray (mSv/Gy); Ka,e-the kerma kinetic energy of the air incident on the body surface, in gray (Gy).

6.1.2 Effective dose conversion factor

6.1.2.1 Refer to Table G.1 in Appendix G for the effective dose conversion coefficients of the six common posture photographic adult reference persons.

6.1.2.2 The effective dose conversion coefficients of two common posture photography for 5-year-old and 10-year-old children are shown in Table G.2 in Appendix G.

6.1.2.3 When estimating the effective dose of a particular subject, if the size and quality of the subject are the same as the adult male, female or adult One of the children's mannequins is similar in size and quality, so you can directly use Table G.1 or Table G.2 in Appendix G. Effective agent The estimation of the amount has a certain influence. When using the effective dose conversion coefficient table, try to take a dose that is close to or larger than the subject's imaging field. Conversion factor.

6.1.2.4 The estimation of the effective dose of ordinary X-ray photography subjects can be used for image quality comparison or optimization, and should not be used directly for radiation hazards risk assessment.

6.2 Effective dose of computed tomography subjects

6.2.1 Effective dose calculation formula The effective dose is calculated according to formula (10). E=CE,CT·PKL,CT (10) Where. E

--- effective dose, the unit is millisievert (mSv); CE, CT

---The effective dose conversion coefficient of the subject caused by CT scan, the unit is millisievert per milligy centimeter [mSv/(mGy·cm)]; PKL, CT

---CT scan of the air kerma length product, the unit is milligray centimeters (mGy·cm).

6.2.2 Obtaining the product PKL and CT of the length product of air kerma kinetic energy

6.2.2.1 It is preferred to read directly from the radiation dose structured report (RDSR) of the CT system.

6.2.2.2 If it cannot be read, use the method of

4.4.2.2 to obtain CVOL first, and then multiply it by the scan length to calculate PKL and CT.

6.2.3 Effective dose conversion factor

6.2.3.1 The conversion coefficients of effective doses for subjects of different ages caused by CT scans of six common positions are shown in Table H.1 in Appendix H. Conversion The coefficient varies depending on the manufacturer and model of the CT device, as well as the different scanning methods and conditions used by different medical institutions. Certain uncertainty.

6.2.3.2 The estimation of the effective dose of the subject of the CT scan can be used for image quality comparison or optimization, and should not be used directly for the risk of radiation hazards Evaluation.