GB 16351-1996 Radiological protection standard for medical gamma-ray teletherapy equipment
Some standard content:
National Standard of the People's Republic of China
Radiological health protection standard on Gamma-beam teletherapy equipment in medicine1 Subject content and scope of application
GB 163511996
This standard specifies the basic requirements for radiological health of medical ray teletherapy (abbreviated as treatment) equipment. This standard applies to the production and use of treatment equipment. 2 Reference standards
GB4792 Basic standards for radiological health protection
3 Terms, symbols, codes
3.1 Rated installed capacity permissible maximum source strength The maximum strength (source strength or activity) of the radioactive source allowed to be loaded in the treatment equipment. 3.2 Useful beam useful beam
Ray from the radioactive source for treatment purposes. 3.3 Leakage radiation All radiation from the radiation source or the treatment equipment head (hereinafter referred to as the head) in addition to useful radiation. 3.4 Nominal value source output in accordance with standard The output or source intensity value of the source given by the competent authority when the radiation source leaves the factory, and its total uncertainty is not more than 2%. 3.5 Nominal value source output during the radiation protection measurement The output or source intensity value of the radiation source attenuated to the monitoring time. It is calculated by the time decay theory using the nominal value of the source. 3.6 Asymmetry unsymmetry
The difference in the same physical quantity between corresponding points on the plane relative to a specified center. If there is no difference between the corresponding points, this situation is called symmetry.
3.7 Uncertainty
The degree to which the value given by the measurement deviates from the agreed true value. It reflects the combined influence of systematic error and random error on the expected result. 3.8 Source-surface distance (SSD) The distance from the radiation source to the central surface of the patient's skin irradiation field. 3.9 Penumbra
Because the radiation source is a non-point source, it has a certain volume and the scattering of the radiation in the irradiation field is inconsistent with the thickness of the useful radiation passing through the collimator, there is a gradual change area of dose from large to small near the edge of the irradiation field. This area is called penumbra. 3.10 Collimator
A device that limits the radiation irradiation direction and determines the size of the irradiation field. Approved by the State Administration of Technical Supervision on May 23, 1996 and implemented on December 1, 1996
3.11 Counterweight| |tt||GB16351—1996
A component on a rotational therapy machine. When the machine is rotating, it balances the weight of the machine head. It has two forms, one that only balances; the other that can also shield radiation. The counterweight mentioned in this standard refers to a counterweight that has both a balancing and radiation shielding function.
3.12 Interlock
When the radiation source is in operation, a device that automatically terminates the radiation therapy once a person enters the treatment room by mistake. 3.13 Central-axis
A straight line passing through the center of the radiation source and the symmetry center of the collimator. 3.14 Isocenter
A fixed point in space that must be referenced during rotational therapy. When the treatment machine rotates, the working state in which its rotation center and the irradiation center of the radiation beam can coincide with this point is called isocenter. 4 Technical requirements
4.1 Principle of dose equivalent limitation
4.1.1 During treatment, the exposure of staff and the public shall be controlled in accordance with the requirements of GB4792. 4.1.2 In treatment practice, the design, supervision and management related to radiation protection must comply with the principles of justification of radiation practice and optimization of radiation protection, so that all necessary exposure is kept at the lowest level that can be reasonably achieved. 4.2 Technical requirements for treatment equipment
4.2.1 The intensity of the radiation source (referred to as source intensity or source) in medical treatment equipment must be no less than 37TBg (1000Ci). 4.2.2 The relative error between the monitored value and the nominal value of the useful radiation air kerma rate at 1m away from the source is less than 10%. 4.2.3 The asymmetry of the useful radiation air kerma rate in the irradiation field is less than 5%. 4.2.4 The timing error of the timer is not more than 1%. 4.2.5 The distance error of the treatment machine to the center position is not more than 4mm. 4.2.6 The distance error of the center axis indicator indicating the center position is not more than 2mm. 4.2.7 The width of the trimmed penumbra should be less than 10mm. 4.2.8 The distance between the boundary line of the light field and the boundary line of the irradiation field is not more than 3mm. 4.2.9 The position indication error of the source-skin distance indicator is not more than 3mm; during treatment, the source-skin distance is not less than 60cm. 4.3 Safety protection requirements for treatment equipment
4.3.1 When the source is placed in the storage position, the air kerma rate of the radiation leaked from the head is limited to: 4.3.1.1 At any position 5 cm away from the head surface, it is not more than 200μGy/h. 4.3.1.2 At any position 1 m away from the source, the average is not more than 10μGy/h, and the maximum is not more than 50μGy/h. 4.3.2 When the source is placed in the irradiation position, the air kerma rate of the radiation leaked from the head at 1 m away from the source is: when the source is not more than 185TBg, it is not more than 0.1% of the air kerma rate of the useful radiation at 1 m away from the source; when the source is more than 185TBq, it is not more than 0.05%. 4.3.3 The transmittance of the collimator to the useful radiation is not more than 2%. 4.3.4 The transmittance of the counterweight to the useful radiation is not more than 0.1%. 4.3.5 The β contamination level on the surface of the treatment equipment caused by the leakage of radioactive materials in the source box must be less than 3.7Bq/cm. 4.3.6 The gas system must provide sufficient air pressure to ensure that the radioactive source drawer does not get stuck or stop during the continuous 100 source delivery per day.
4.3.7 The head and collimator must be able to be locked in any required position, and there must be protective measures to prevent the head from pressing the patient. 4.3.8 When the power outage or accident interrupts the treatment, the radioactive source should be able to automatically return to the storage position. 4.3.9 The treatment equipment should be equipped with a useful radiation monitoring instrument and interlocked with the source position switch. 4.4 Testing requirements and methods
4.4.1 When testing according to the technical indicators of this standard, the following types of instruments shall be selected according to the purpose of the test:74
GB16351—1996
4.4.1.1 When measuring useful radiation, use an ionization chamber type measuring instrument. The volume of the ionization chamber is not more than 1cm, and the measurement uncertainty is less than 5%.
4.4.1.2 When performing protection measurements, use an ionization chamber and a counter tube type measuring instrument, and the measurement uncertainty is less than 30%. 4.4.2 When performing contamination (β-ray) detection, use a surface contamination inspection instrument. The detection efficiency is not less than 20%, and the detection area is not less than 50cm2. 4.4.3 When performing detection according to this standard, all types of detection instruments used must be calibrated and used within the specified validity period. 4.4.4 When performing detection according to this standard, the detection method is detailed in Appendix A. 5 Product delivery inspection
5.1 The manufacturer should evaluate the protection performance of the treatment equipment based on the rated installed capacity, and the factory's technical inspection department must conduct inspections in accordance with the requirements of this standard. After passing the inspection, it shall be accepted by the radiation health protection department. 5.2 For any of the following situations, all items specified in this standard must be tested: 5.2.1 Prototypes of newly developed products before they are put on the market. 5.2.2 For products that are normally put into production, a sampling inspection shall be conducted once a year. 5.2.3 Products that are put into production after a one-year interval. 5.2.4 Products whose design, process or materials have been changed. 5.3 The manufacturer shall conduct a product protection performance test in conjunction with the local radiation health protection department, and the test results must be submitted to the protection department for record. 6 Treatment room facility requirements
6.1 The setting of the medical treatment room must ensure the safety of the surrounding environment, and the treatment room must be separated from the control room. The area of the treatment room should be no less than 30m2, and the floor height should be no less than 3.5m.
6.2 The treatment room building must have sufficient shielding thickness. When designing protection, the location and environment must be considered, and attention must be paid to the protection of the roof. The shielding thickness calculation method can be found in Appendix B.
6.3 The entrance to the treatment room must be in the form of a maze. A signal device indicating the working status must be installed at the door. The door must be interlocked with the therapeutic radiation source.
6.4 A treatment room with good ventilation and lighting may not have windows. Only when the treatment room is built separately and is far away (not less than 30m) from non-radiation buildings, can windows be installed on the roof or high on the wall in the direction not of useful radiation projection, and the area should not be larger than 1m. 6.5 The control room should be equipped with monitoring or intercom devices, such as observation windows. The window must have the same protective effect as the side wall. 6.6 In the control room, the safety signal indicator light on the equipment operation console to show that the radiation source is in the "irradiation" or "storage" position must be synchronized with the status indicated by the display device on the treatment machine. 6.7 The treatment room should have good ventilation. The air exchange rate during mechanical ventilation is generally 3 to 4 times per hour. 75
A1 Useful ray air kerma rate test GB16351—1996
Appendix A
Selection and measurement and calculation method of inspection point (supplement)
The source is placed at the irradiation position, the maximum irradiation field is taken, the probe of the measuring instrument is placed on the central axis of the beam 1m away from the source in the direction of the useful ray outlet, and the measurement is carried out without any scatterer within 2m from the source. Calculate the error according to formula (A1): E
?×100
Where: 7——Relative error between monitoring value and nominal value, %; E. —Nominal value during monitoring, Gy/min; E
Monitoring value, Gy/min.
A2 Determination and measurement and calculation method of the monitoring point position of useful ray asymmetry. (A1)
Figure A1 is a schematic diagram of the useful ray asymmetry inspection measurement point. In the figure, the box is the irradiation field, which is 10×10cm2 in size. Point 0 is the center of the irradiation field. Each black dot is a checkpoint, which is 4cm away from point ○ and 1cm away from the edge of the irradiation field. Place the source at the irradiation position, take the commonly used source-skin distance and the irradiation field of 10×10cm, and measure the positions of the points shown in Figure A1. 0
Use formula (A2) to calculate the asymmetry value:
Where:—asymmetry percentage, %;
0×100
E, monitoring value of the center point of the irradiation field, Gy/min; amax—the maximum value of the difference between the measured values of each monitoring point, Gy/min. A3 Check of the timer running error
（A2）
In the same time interval, take the running time of the calibrated electronic watch as the standard, and compare the running time of the timer on the treatment machine with it, and the comparison time interval shall not be less than 5min. Use formula (A3) to calculate the timer's running error: to
Where: n—Percentage of running error, %; 76
(A3)
to-Time recorded by the electronic watch, min;
t—Time recorded by the timer, min.
A4 Method for checking the same center position
A4.1 Mechanical same center inspection
GB 16351—1996
Take a square wooden block (length, width and height are all 10cm), and embed a 10cm long wooden strip in the center of the side. One end of the wooden strip is square, the other end is round, and the diameter is 4mm. Insert the square end into the wooden block and fix it, as shown in Figure A2. Stick ordinary coordinate paper around the wooden block and mark the center of each side. Then use a piece of white paper to make a cylinder about 10 cm long, so that it can just fit on the round end of the wooden strip. Draw a crosshair on the white paper, and place the wooden block on the treatment bed so that its ABCD plane is parallel to the irradiation direction (Z) of the central beam (see Figure A2a.), so that one line of the light field crosshair projection image coincides with the AD side, and the other line coincides with MN. The intersection point (center) of the two crosshair lines coincides with point O. Rotate the machine at 0°45°, 90%, 135°, 180°, 225°, 270°, 315°, and 360°, and record the position of the crosshair center point on the ABCD plane at each angle. These positions (points) form a circular trajectory. By measuring the maximum distance of this trajectory, the deviation 3 of the same center position on the Y plane can be obtained (see Figure A2a.). Then, the crosshairs on the thin rod of the wooden block are completely aligned with the image of the irradiation field crosshairs, and the treatment machine is rotated according to the above angle. The position of the center of the irradiation field crosshairs on the white paper tube when the angle is different is recorded. Remove the paper and cut it along the X axis. At this time, the distance between the trajectories of the points on the white paper is the deviation of the co-center position on the X axis (see Figure A2b.). Figure A2
A4.2 Useful beam co-centering check
GB16351-1996
≤3.4cm (if the beam width is 3cm)
Continued Figure A2
Use slow-sensitive film photography to determine the method. Take two films, wrap them with light-proof paper, and number them. The first step is to make a co-centering check in the Y direction (the direction indicated by the Y axis in Figure A2a. and b., the same below). Place the first (No. 1) film at the same center position and perpendicular to the rotation axis (i.e., X-axis) of the machine, i.e., in the Y-Z plane. Open the pair of collimator blocks along the X-axis direction of the machine as much as possible, and close the pair of collimator blocks along the Y-axis direction as much as possible. In many machines, when the collimator is completely closed, due to the structure, the two pairs of collimator blocks form the narrowest rectangular hole of about 3 or 4 cm. With this adjustment just now, the collimator forms a long slit (narrow rectangle) of about 3 or 4 cm wide. Move the radiation source to the irradiation position, and let the machine rotate in nine directions of 0°40°80°, 120°, 160°, 200°, 240°, 280°, and 360°, and expose the film in turn. The image on the film after exposure is shown in Figure A2c. This figure is called a "starshot ring". It is a concentric geometric image of useful rays in the Y-Z plane, which represents both the concentricity in the Y direction and the concentricity in the Z direction. The maximum size of this image should not exceed the sum of the irradiation field width plus 4mm. The second step is to check the concentricity in the X direction. Close the pair of collimator blocks along the X-axis as much as possible, and open the collimator blocks along the Y-axis as much as possible. The collimator forms a narrow hole opposite to the above situation. Bring the source to the irradiation position and place the second film in the same center position, but parallel to the rotation axis (i.e. in the X-Z plane). Then, similar to the first film, irradiate the second film in nine directions. The image on the film is shown in Figure A2d. This is the center of the useful beam in the X direction. The width of this image should not exceed the sum of the irradiation field width plus 4 mm. A4.3 Rapid mechanical centering check method
Place a mechanical pointer along the center axis of the beam (z axis) and a tip with a diameter not greater than 2 mm along the horizontal direction (X axis). mm indicator rod, adjust the height of the pointer to the source axis distance SAD-2mm (SAD is the distance from the source to the same center). When the treatment head rotates with the pointer, the distance between the pointer tip and the top of the indicator rod can be measured. In the Y-Z direction, the difference between the two should not be greater than 8mm, and in the X-axis direction, it should not be greater than 4mm. Otherwise, it will exceed the 4mm requirement for the same center. A5 Center Axis Position Deviation Check
Put a piece of white paper on a plane perpendicular to the center axis so that the projection image of the light field crosshairs is aligned with the white paper. The crosshairs on the paper overlap. At the commonly used source-skin distance, place the machine head in the vertical and horizontal positions, rotate the collimator, and record the distance between the crosshairs and the crosshairs on the white paper. This indicator can also be checked by replacing the crosshairs with a pointer fixed to the collimator. A6 Determination of the position of the penumbra monitoring point
Figure A3 is a point distribution diagram for determining the dose measurement in the penumbra area. The irradiation field shown in the figure is a square irradiation field with a size of 10×10cm. Point 0 is the center of the irradiation field, and the black dots indicate the position of the measuring points. The distance between each black dot is 0.5cm, 20 measuring points in total. 78
GB16351-1996
Testing the width of the penumbra area, take the commonly used source-skin distance and the irradiation field of 10×10cm2, and take 5 (total 20) measuring points (see Figure A3) at equal distances from the center of the irradiation field in the range of 4 to 6cm. Compare the measured values of each point with the measured value of the center point to calculate the percentage, and use the distance in the range of 80% to 20% in the distance-percentage curve to represent the width of the penumbra. A7 Checking the distance between the irradiation field and the boundary line of the light field Measure and draw according to the A6 method, take the position of 50% of the curve to represent the boundary of the irradiation field, and then compare it with the boundary line determined by the light field to find the distance between the two boundaries. A8 Checking the position deviation of the source-skin distance
Method 1 Place a piece of white paper on the treatment bed so that its distance from the tip of the source-skin distance mechanical indicator rod does not exceed 1mm. Then remove the indicator rod, use the optical source-skin distance indicating system to indicate the source-skin distance at this time, and measure the deviation between the two. Method 2 Adjust the source-skin distance to the commonly used source-skin distance (for example, 80cm), adjust the irradiation field to 10×10cm2, and measure the air kerma rate E of useful rays in the range of 60cm to 100cm. Then, take the reciprocal of the square root of the result E, that is, 1/VE. Draw a curve on ordinary coordinate paper about the relationship between the measured distance and the reciprocal of the square root of the measured value E, that is, r-1/√E. This is a straight line. Extrapolate this straight line to the origin of the coordinate axis. The intersection of this straight line and the distance axis is 1% of the source-skin distance under examination (for example, 8mm for a source-skin distance of 80cm), or less. The source-skin distance position deviation meets the requirements specified in the index. A9 Nose leakage ray inspection
A9.1 Determination of the nose leakage ray monitoring point Figure A4 is a schematic diagram of the location of the nose leakage ray monitoring point. In the figure, point O is the location of the radiation source, the Z axis is the direction of useful radiation, the X axis is the rotation axis of the treatment machine, the Y axis is perpendicular to the X-Z plane, and a sphere is constructed with the source point O as the center and 1m as the radius. The upper and lower vertices on the sphere are defined as points 1 and 2 (on the Z axis), and the four points equidistant on the spherical equator (i.e., the circle on the X--Y plane) are defined as points 3, 4, 5, and 6, of which 3 and 5 are on the Y axis, and 4 and 6 are on the X axis. Connecting the six points 1, 2, 3, 4, 5, and 6, the entire sphere forms eight spherical triangles. Take points at the center of these triangles. A total of eight points 7, 8, 9, 10, 11, 12, 13, and 14 are formed. The most basic monitoring points for measuring the leakage of radiation from the machine head are these 14 points. There is also a 26-point monitoring method, which is more complicated and will not be introduced here. The method for measuring the 14 points is to project the position of the machine head source center O on the ground, recorded as O'. Draw a circle with O' as the center and 1m as the radius, and draw a straight line O'X' (i.e. the projection line of the coordinate OX axis on the ground) from the center point O' with the front of the nose (i.e. the X-axis direction) as the starting direction. Take the intersection point A of this straight line and the circle as the origin, and take 8 points on the circumference with central angles of 45°, 90°, 135180225°270315360° (0°), i.e. points B, C, D, E, F, G, H and A in the figure. Place the probe of the measuring instrument on the ground at a central angle of 90° (point C) and 270° (point G), with the height facing the radiation source of the machine head. At this time, points 3 and 5 in Figure A4 can be measured; rotate the machine head to measure points 1 and 2; move the measuring probe to 135° (point D) or 225° (point F), keep the probe height unchanged, and rotate the machine head 45 degrees up and down at the original position to measure 10 and 14, 9 and 13, and then move the probe to 45° (point B) or 315° (point H). The probe height remains unchanged, and the machine head rotates 45° up and down to measure 7 and 11, 8 and 12. Finally, move the probe to 0° (point A) or 180° (point E) to measure 4 and 6. Note that because point E is at the machine base, when measuring this point, the distance should be extended to avoid the machine base in order to place the measuring instrument.
Figure A4 Spatial measurement points of the head and ground projection Figure A9.2 Monitoring of leakage radiation from the head
A9.2.1 Measurement of the radiation source in the storage position For the monitoring point 1m away from the radiation source, take a detection area of 100cm2 at each measurement point for measurement according to the method shown in A4.1: For the monitoring point 5cm away from the head surface, the direction of the point taken at the 1m position is corresponding to 14 points in the area 5cm away from the head surface, and take a detection area of 10cm2 for measurement at each point. A9.2.2 Measurement of the radiation source in the irradiation position Close the collimator to the minimum, and use a lead ingot of not less than 10 half-value layers of thickness to block the outlet of the useful radiation, and then move the radiation source to the irradiation position. Measure according to the method shown in A4.1. A10 Test of the radiation transmittance of the collimator
Take the commonly used source-skin distance and the irradiation field of 10×10cm2, and take 4 points symmetrically distributed 2cm outside its boundary. Then close the irradiation field to the minimum. Use lead ingots with 6 half-value layer thickness to block the outlet of the useful ray for measurement. Calculate the transmittance using formula (A4). ×100
Where: n—percentage of transmittance, %;
Air kerma rate of the ray passing through the collimator, Gy/min, E,——Air kerma rate of the ray at the center of the irradiation field, Gy/min. 80
A11 Test of the transmittance of the ray of the balance hammer
GB 16351--1996
Turn the treatment machine so that there is no scatterer within 2m of the source in the direction of the useful ray. Adjust the irradiation field so that it is at the boundary of the irradiation area on the upper surface of the balance hammer, and the distance from the edge of the surface is not less than 10cm. Place the measuring instrument on the central axis of the useful ray, 15cm away from the bottom of the balance hammer, and measure.
Use formula (A5) to calculate the transmittance: www.bzxz.net
Where: 7—Percent transmittance, %;
E.—Measurement value through the counterweight, Gy/min; iw—Measurement value at the same point without the counterweight, Gy/min. A12β Radioactive Material Contamination Inspection
Method 1 Place the source in the storage position, remove the organic glass tray below the useful ray outlet, and use the contamination inspection instrument to directly measure the β contamination on its surface.
Method 2 For the treatment machine without a tray below the useful ray outlet, place the source in the storage position, take 5 pieces of 2×10cm2 adhesive tape, and stick them flatly on the inner surface of the collimator on the useful ray outlet, and take samples for measurement. The wiping sampling method can also be used for measurement. A13 Gas Supply Pressure Inspection
Make the pressure gauge in the low pressure range of 2 to 3kg/cm2, and perform a source drawer delivery simulation experiment every 2 minutes. There should be no jamming or stopping during the 100 source delivery experiments. Appendix B
60CoY Shielding Thickness Calculation for Radiation Therapy Room (Reference)
B1 Calculation formula for the thickness of the shielding wall of the treatment room concrete (p=2.35g/cm3) B1.1 Calculation formula for the thickness of the wall to prevent useful radiation and leakage radiation △ = 7.36(ln[(2.24 + 4.24lnK)Kea.025aJ)cosaA = 7.36 (lnC(-4.4 + 5.4lnK)Keo.025aJ)cosa Where: △
Calculated wall thickness value, cm;
—The attenuation factor of useful radiation or leakage radiation; —The angle between the radiation and the normal of the shielding wall, (°). B1.2 Calculation formula for anti-scattered ray wall thickness
In(2Ky)
A= 0.0827 + 0.000 7264
武中; K-
scattered ray attenuation factor;
虫-scattering angle, (°).
The meanings of other symbols in the formula are the same as those in B1.1.
102≤K<101
（B1）
+**(B2 )
（B3)
B2 Calculation of lead equivalent of treatment room door
GB 16351—1996
B2.1 Calculation formula of lead equivalent of Z-type labyrinth protection door△z.Ph = 0. 89 In(2Kz)
Where: Az.bz Labyrinth protection door lead equivalent, mm; Kz——Z labyrinth entrance ray attenuation multiple.
B2.2 Calculation formula of lead equivalent of L-type labyrinth protection door△L,Pb = 1. 26 ln(2K,)
Where: AL.Ph—
-L Labyrinth protection door lead equivalent, mm;
I Labyrinth entrance radiation attenuation multiple.
Appendix C
Y Treatment equipment manual essential contents
(reference)
C1 Equipment performance description
Equipment protection performance.
C1.2 Equipment quality inspection certificate.
C1.3 Product protection identification certificate.
C2 Radioactive source performance description
The strength and geometric dimensions of the radioactive source.
The test results of the sealing performance and contamination of the source box. C2.3
The air kerma rate and calibration date at 1m from the source. Radioactive source quality inspection certificate.
Additional notes:
This standard is proposed by the Ministry of Health of the People's Republic of China. This standard is drafted by the Sichuan Provincial Radiation Health Protection Institute, Chengdu Municipal Health and Epidemic Prevention Station, and the Affiliated Hospital of West China Medical University. The main drafters of this standard are Chen Jingzhong, Zhu Zeyuan, Zhang Xinhua, Xie Mingying, Mou Changrong, Luo Dengxiang, Du Guangheng, Lu Zhiming, etc. The Ministry of Health entrusted the Ministry of Health's Industrial Hygiene Laboratory, the technical unit responsible for the interpretation of this standard. 82
（B4）
·（B5）
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