AAPM REPORT NO.
AAPM REPORT NO. 25 PROTOCOLS FOR THE RADIATION SAFETY SURVEYS OF DIAGNOSTIC RADIOLOGICAL EQUIPMENT A REPORT OF THE DIAGNOSTIC X-RAY IMAGING COMMITTEE TASKGROUP Pei-Jan Paul Lin (Chairman), Northwestern University, MedicalSchool Keith J. Strauss (Co-Chairman), The Children’s Hospital, Boston Burton J. Conway, Center for Devices and Radiological Health Jane R. Fisher, Polyclinic Medical Center, Harrisburg Robert J. Kriz, University of Illinois, Hospitalat Chicago Mary E.
DISCLAIMER: This publication is based on sources and information believed to be reliable, but the AAPM and the editors disclaim any warranty or liability based on or relating to the contents of this publication. The AAPM does not endorse any products, manufacturers, or suppliers. Nothing in this publication should be interpreted as implying such endorsement. Further copies of this report may be obtained from Executive Officer American Association of Physicists in Medicine 335 E.
Contents Introduction and General Clarifications Introduction ------------------------------- 1 General Clarifications --------------------Part I. 1 Medical Radiographic Installations I-l. Introduction ------------------------- I-2. System Information ------------------- 3 I-3. Beam-on Control Indicators ----------- 4 I-4. Shielding Devices -------------------- 3 4 The Source-to-Image Receptor Distance ----------------------------- 5 Fixed Radiographic Unit ------------ 5 I-5-A.
Radiographic Installation Checklist -------- 19 Part II. Medical Fluoroscopic Installations II-l. Introduction---------------------------- 22 II-2. Exposure Switches and Interlocks ------- 22 II-3. Fluoroscopic Timer --------------------- 22 II-4. Lead Protective Devices ---------------- 23 II-5. Minimum Source to Skin Distance (SSD) ---------------------------------- 23 II-5-A. Measurement of SSD ------------------- 24 II-6. Radiation Beam Restriction and Alignment -----------------------------II-6-A.
III-2. Beam-on Controls and Indicators ------ 38 III-3. Minimum Source-Skin Distance: Intraoral Unit ----------------------- 38 III-4. Source to Image Receptor Distance: Cephalometric Unit ------------------- 39 III-5. Radiation Beam Restrictors ----------III-5-A. Intraoral System ------------------III-5-B. Panoramic System ------------------III-5-C. Cephalometric System --------------III-5-D. Labeling of Cones or Apertures ----- 39 39 40 40 40 III-6.
Introduction and General Clarifications Introduction The task group: "Protocols on The Radiation Safety Survey of Diagnostic Radiological Equipment" was formed by the Diagnostic X-ray Imaging Committee to provide a unified approach to radiation surveys of x-ray imaging equipment conducted by radiologic physicists. Stationary and mobile radiographic, fluoroscopic, dental x-ray, and mammographic equipment are covered. its Due to specialized requirements computed tomography (CT) equipment is not.
2. Determine typical patient exposure levels for standard radiographic exams and fluoroscopy, 3. Assess fluoroscopic contrast and spatial resolution, 4. Evaluate radiographic image quality, and 5. Review processor quality control procedures. These quality assurance efforts are beyond the scope of this report. The performance levels cited from Reference 1 do not apply to non-certified components.
Part I: Medical Radiographic Installations I-l. Introduction Pages 19-21 contain a checklist of the physical parameters to be evaluated and the information pertinent radiation protection survey of radiographic to the information instal-lations. The record keeping identified in the checklist normally has practical value in identifying the radiographic unit under evaluation. If information concerning the certification status of the unit or warning labels affixed to the control panel, etc.
I-3. Beam on Controls and Indicators Verify the availability of a positive indicator of x-ray production when the x-ray tube is energized, such as: (a) mA-Meter, (b) X-ray "on" light, and/or (c) Audible signal during or at end of exposure. Any of Test their function by making x-ray exposures. these three warning systems which are provided should be switch should be a functioning. The x-ray exposure deadman type switch; the exposure must terminate when pressure on the switch is released.
The surveyor should verify the presence and use of shielding devices. The surveyor should check or monitor apparel. The shielding protective the checking of apparel should be examined fluoroscopically. The results should be documented as required by the JCAH. These checks should be completed at least annually. I-5. The Source-to-Image Receptor Distance Most general radiographic units have a variable SID Head units often (source-to-image receptor distance). have a fixed 32" (81 cm) or 36" (91 cm) SID.
devices have been developed to expedite this. Hendee and plastic cylinder for Rossi, for example, employ a Localization of the focal measuring SID (Reference #3). spots on tubes should be performed as part of acceptance testing of newly installed x-ray tubes. A repeat of this measurement usually is not necessary until the x-ray tube is replaced. i-5-B.
Set a standard x-ray field size, 18 x 24 cm (8 x 10"), using the appropriate numerical indicator scale on the collimator. Turn on the collimator light field and place 4) radiopaque markers on the table top to delineate the edges of the light field. Expose the cassette with a technique that 5) results in an optical density range of l-l.4 on the film. Open collimator blades and without moving 6) the markers or cassette make a second exposure using l/5 the mAs used in step 5.
on the x-ray tube assembly. X-ray Field/Numerical Indicator Size: I-6(c) Measure the length and width of the x-ray field on each film. These dimensions should agree with the numerical values originally set in step 3 above to within 2% of the SID (Reference #l). Most units have more than Each of these scales one numerical indicator scale. The units displayed on the references a specific SID. scales (metric vs English) should match the units used to size the typically used cassettes.
test methods which require no Three different special instrumentation are described below. Test Method I 1) Place the collimator in automatic mode. Center a small cassette, 18 x 24 cm 2) (8 x 10"), in the cassette tray. 3) Center a larger cassette on the table top. 4) Make an exposure. Process the film. If the x-ray field 5) size exceeds the film size in the cassette tray, use triangulation and the radiograph from the table top to determine the actual x-ray field size at the cassette tray.
Caution: Some PBL collimators do not have a key designed to-disable their automatic sizing as required in step 3 of Method II. If this key is not provided and the automatic collimation feature cannot be readily disabled, method I or III must be used. Method I has the same precision, but less accuracy than Method II. Method III is both less precise and less accurate than Method II.
lock out exposures the operator has manually until adjusted the x-ray field to be smaller or equal to the size of the image receptor. The function and sizing accuracy of the PBL should be checked at least annually or after any repairs to the PBL sensors in the cassette holder, drive motors in the collimator, or electronics of the PBL. I-7. Primary Radiation Beam Characteristics The penetrating quality of an x-ray beam is characterized by its half value layer (HVL).
the HVL measurement. The test protocols of the following two sections the HVL to determine describe methods to measure Since compliance with minimum filtration requirements. the HVL is a function of the actual high voltage applied to the x-ray tube, the protocols assume the unit's kV calibration is correct.
concerning compliance with minimum filtration requirements. For example. if the actual kV is lower than indicated on the operator's console, the measured HVL might not meet the minimum HVL specifications even though adequate filtration is in the beam. Likewise, if the kV is higher than indicated, the measured HVL might appear to be adequate even though the filtration in the beam is inadequate. I-7-A.
7) Compare the measured HVL against "Table IMinimum HVL Requirement" to determine compliance. Test Method II: Units With No Manual Timing 1) Place the unit in Automatic Exposure Control (AEC). 2) Place the ionization chamber a few inches away from table top or wall cassette holder to reduce backscatter. The chamber should be positioned over the center of the AEC sensor. 3) Collimate the x-ray field to a size slightly larger than the larger of the ionization chamber or AEC sensor.
filtration may be necessary as discussed in Section 1-7A. This abbreviated test method can also be applied to step #8 in Test Method II in section I-7-A. I-7-C. Radiation Exposure and Expected Output After verifying correct filtration of the unit, the radiation output of the x-ray unit should be measured at several tube potentials with the tube current stations routinely employed clinically.
(g) X-ray tube age. If the measured radiation output deviates more than 40-50% from the appropriate value suggested in Table III, the generator may need a complete kV, mA, and time calibration. However, previous generator calibration and radiation output measurements should be consulted. The values in Table III are not applicable to falling kV generators such as capacitor discharge units which do not have constant mR/mAs values at different mAs stations.
high voltage cables contributes to the actual output of While this contribution each exposure (Reference #21). to the measured mR/mAs is less than 5-10% for tube currents above 200 mA and exposure time settings greater than 0.05 seconds, exposure measurements obtained with tube currents less than 25 mA and exposure time settings less than 0.005 seconds can be two to three times higher than the predicted values in the last column of Table III (Reference #21).
items should be included on the survey forms. A recommendation or a suggestion should accompany each item in an effort to bring the unit into full compliance with the effective radiation rules and regulations. It may also be necessary to contact service engineers to rectify identified problems. The radiological physicist should also bear in mind that x-ray equipment operators may not have received any formal radiological training concerned with the safe operation of a particular piece of equipment.
Checklist Outline for Radiographic Installations I-2. SYSTEM INFORMATION Installation A. 1. Date of survey 2. Room number Department/Building 3. Institution 4. Unit identification number B. Generator 1. Manufacturer 2. Model type, model number, serial number 3. Maximum high voltage (kVp) 4. Maximum tube current (mA) X-ray Tube Insert C. 1. Manufacturer 2. Model type 3. Serial number 4. Nominal focal spot sizes a. Large b. Small 5. Leakage technique factors D. X-ray Tube Housing 1. Model number 2.
E. Other Specialized Devices I-5. SOURCE-TO-IMAGE RECEPTOR DISTANCE A. Focal Spot Localization (when x-ray tube is replaced) B. SID indicators 1. Accuracy of numerical indicators 2. Accuracy of detents 3. Accuracy of tape measure C. Mobile or portable SSD accuracy I-6. RADIATION BEAM RESTRICTORS AND LIGHT LOCALIZERS X-ray Field/Light Field Congruence (at least A. annually or after removal of collimator) 1. Large cassette 2. Small cassette X-ray Field/Cassette Tray Alignment (at least B.
(at least annually or as in I-7.A) I-8. RADIOGRAPHIC TECHNIQUE CHART Availability A. Use B. Completeness C. I-9. IDENTIFICATION OF PERSON CONDUCTING EVALUATION Name A. Title B. Professional Certification C. I-10. RECOMMENDATIONS AND SUGGESTIONS I-11. POSSIBLE ADDITIONS In-room Stray and Scatter Radiation Levels A. (see Section IV-3) Protective Barrier/Shielding Survey (See B. Section IV-4) C. Leakage Radiation (See Section IV-2) Use and Presence of Personnel Monitoring D.
Part II. Medical Fluoroscopic Installations II-l. Introduction Pages 34-37 contain a checklist of the physical parameters which require evaluation and the information important to the radiation protection of survey fluoroscopic installations. Some of these parameters and information are similar to those of radiographic installations. While this part's checklist is complete, only the parameters and information unique to fluoroscopic installations are discussed here. II-2.
the completion of the elapsed preset time. Re-initiation of the fluoroscopic exposure without resetting the timer shall restart the audible warning (Reference #l). Older. non-certified units and some certified units may terminate the exposure as an alternate to the audible warning. The operation of the timer and audible warning One should verify that the timer should be checked. activates the signal (or shuts off the-radiation) at the termination of the preset time.
capabilities. The 38 cm SSD also applies to lateral plane x-ray tubes found in biplane fluoroscopic systems. Since automatic collimators required on certified stationary fluoroscopic units are usually large in size, the minimum SSD in these cases usually cannot be violated. In fact, many current under table fluoroscopic units are designed with an SSD of 46 cm (18"). The Federal Standard makes one exception to the mobile image-intensified fluoroscopic SSD when used for specific surgical application.
II-6. Radiation Beam Restriction and Alignment describes the evaluation of the This section collimator's ability to automatically restrict the x-ray field size to the size of the selected portion of the image receptor. This parameter should be evaluated at least annually or after any repair or adjustment to 1) blades, 2) collimator collimator drive motors or intensifier tower SID sensing electronics, 3) image device, or 4) cassette holder within spot film device.
3) 4) 5) 6) 7) 8) 9) 10) 11) 12) During fluoroscopy, center the test tool. This process is normally easier if one of the two pair of collimator blades is closed to give a "slit image" with edges parallel to one of the orthogonal channels. Lock the fluoroscopic tower in place when centering is complete. Tape the test tool to the tabletop. Place the collimator in the automatic mode of operation. If automatic mode is not present, open collimator completely using the manual mode.
19) If any question concerning alignment as a function of SID exists, steps 13-18 should be repeated with the tower positioned vertically at the maximum SID. Spot Film Field Sizing 20) Repeat steps l-4 above. 21) Place an unloaded cassette in the spot film device. 22) Place the collimator in the automatic mode and select the full size spot film mode. 23) Place a ready pack film on top of the test tool on the table top. 24) Make three exposures using the technique of step 17. 25) Process the film.
intersecting at the center of the field of view shall not exceed 4 percent of the SID (Reference #1). II-6-C. Evaluation of Spotfilm Alignment Steps 13-19 of Section II-6-A allow evaluation of the alignment of the central ray of the x-ray field and the center of each selected portion of the image receptor within the spotfilm device as a function of the SID. On each image, the diagonals drawn from the corner of each darkened area mark the center of the x-ray field.
II-6-E. Alternate Test Methods The test method briefly described in II-6-A is only one of many. While the test equipment required for this method is minimal, many images must be exposed and processed to completely verify a conventional spot film device and imaging chain. Lin has described in detail the design and use of more expensive test tools which drastically reduce the time required to complete the Hendee and Rossi testing (References #5 and #12).
HVLs for Units With Manual Exposure Rate Controls Fluoroscopic systems with manual exposure rate controls allow use of Test Method I in Section I-7-A with some minor geometry changes. The image intensifier should be set at its maximum SID on under table x-ray tube systems. The added Aluminum test filters are put on the table top while the ion chamber is placed halfway between the table top and spotfilm device.
7) Complete steps #8-#12 of Test Method II found in Section I-7-A. HVL Test Method II: Noninvasive, Maximum kVp Test Point 1) Use identical geometry described in steps 1 and 2 in Test Method I, Section II-7-A. 2) Place an Aluminum or Copper attenuator (1" or 1 mm thickness respectively) in the beam to protect the image intensifier from unattenuated x-rays. 3) Adjust the collimator during fluoroscopy to minimize the x-ray field size at the ionization chamber.
for the high mode. exposure rate However, it is considered good practice to limit this mode to 10 R/min (2.6 mC/(kgmin)) unless a specific clinical need has been identified. The entrance exposure rate of fluoroscopic equipment without AERC, shall not exceed 5 R/min (1.3 mC/(kgmin)) during fluoroscopy unless the unit is provided with an optional high exposure rate control (Reference #l). If the unit is provided with this option the comments about high exposure rate control in the previous paragraph apply.
assembly. When the maximum entrance exposure of a unit is measured, the lead plate protects the image intensifier from excessive entrance exposure rates. Also, it is good practice to avoid long exposures at the maximum factors minimizing the chance of exceeding the thermal rating of the x-ray tube. These measurements should be completed at least annually or after replacement of the x-ray tube, generator recalibration, filter thickness change or adjustment to the AERC. II-7-D.
Checklist Outline for Fluoroscopic Installation II-l. SYSTEM INFORMATION (See Section I-2) A. Installation 1. Date of survey 2. Room number 3. Department/Building 4. Institution 5. Unit identification number B. Generator 1. Manufacturer 2. Model type, model number, serial number 3. Maximum high voltage (kVp) 4. Maximum tube current (mA) C. X-ray Tube Insert 1. Manufacturer 2. Model type 3. Serial number 4. Nominal focal spot sizes a. Large b. Small 5. Leakage technique factors D. X-ray Tube Housing 1.
II-3. FLUOROSCOPIC TIMER A. Five Minute Maximum Setting B. Audible Warning Functional C. Accuracy of Elapsed Exposure time (at least annually or after repairs or replacement) II-4. SHIELDING DEVICES AND APPAREL A. Lead Drape 1. Presence 2. Condition B. Bucky Slot Shield 1. Presence 2. Working condition 3. Adequacy C. Table End shield Presence D. Aprons (See Section I-4-A) 1. Available 2. Employed E. Gloves (See Section I-4-B) 1. Available 2. Employed F. Gonadal Shield (See Section I-4-C) 1. Available 2.
B. Fluoroscopic Mode Alignment and Sizing (Maximum SID, auto and/or manual mode) 1. Large FOV (14", 13, 12", 11", 10", or 9") 2. Medium FOV (10", 9", 7", or 6") 3. Small FOV (6", 5", or 4 l/2") C. Spot Film Alignment (minimum SID) 1. 1 on 1 2. 2 on 1 a. Longitudinal b. Transverse 3. 4 on 1 4. 9 on 1 5. etc. D. Spot Film Alignment (maximum SID) 1. 1 on 1 2. 2 on 1 a. Longitudinal b. Transverse 3. 4 on 1 4. 9 on 1 5. etc. E. Spot Film Field Sizing (minimum SID, auto and/or manual mode) 1. 1 on 1 2. 1 on 1 a.
C. Qualitative Evaluation of AERC Device (same frequency as II-7.B II-8. IDENTIFICATION OF PERSON CONDUCTING EVALUATION A. Name B. Title C. Professional Certification II-9. RECOMMENDATIONS AND SUGGESTIONS (See Section I-10) II-10. POSSIBLE ADDITIONS A. In-room Stray and Scatter Radiation Levels (See Section-IV-31 B. Protective Barrier/Shielding Survey (See Section IV-4) C. Leakage Radiation (See Section IV-2) Presence of Personnel Monitoring D.
III. Dental Radiographic Installations III-l. Introduction Many items discussed in the Medical Radiographic Installation Section, Section I, are applicable to dental x-ray units. Pages 45-47 contain a checklist of the physical parameters which require evaluation and the information important to the radiation protection survey of dental radiographic installations. While this section's checklist is complete, only information and parameters unique to dental installations are discussed here.
SSD shall be 10 cm (4") (Reference #L). The distance between the end of the cone attached to the tube head assembly and focal spot usually can be measured with a tape measure. If the location of the focal spot is not indicated or if the tube has been replaced since the Section I-5-A for measurement previous survey, see details. an SSD for Federal standards do not specify units.
an appropriate image receptor which is larger than the xray field placed at the distal end of the cone. The image receptor can be film, fluorescent screen, etc. III-5-B. Panoramic System The rectangular slit within the cone mounted on the x-ray tube assembly should restrict the size of the x-ray beam to a size smaller than the slit opening on the image receptor support housing.
apertures these interchangeable cones. or shall have permanent labels which indicate the image receptor size and SID for which the beam restrictor is designed (Reference #1). III-6. HVL Measurement radiation beam quality on Measurement of Cephalometric and Intraoral units is a straight forward process. The comments of Sections I-7, I-7-A, and I-7-B apply. Special care must be used to make HVL measurements on Panoramic units. These x-ray units have long exposure wait 5 minutes between times.
for Devices and Radiological Health (CDRH) of the US Department of Health and Human Services (USDHHS), has documented that dental film development is a major problem (Reference #15). In a typical full mouth intra oral radiographic examination, a patient is subjected to 14 to 20 exposures. The entrance exposure of overlapped areas is high and can be excessive unless the film is properly developed.
The general comments of Section I-7-C on measuring radiation exposures apply to dental x-ray units. The ionization chamber and electrometer described in Section measurements on I-7-D are appropriate for these Most dental units are Cephalometric or intraoral units. single phase halfwave or full wave rectified units. The expected exposures at 24" from the x-ray source as a function of kV are listed in Table III, Section I-7-C.
The mechanical support of the x-ray tube on Cephalometric and Panoramic units shall be designed so that the x-ray tube housing assembly remains stable during an exposure after positioning. This should be evaluated on intraoral the x-ray tube assembly in the units by placing positions/angles commonly used clinically. The cephalometric unit should be set up in its clinical geometry to evaluate mechanical stability.
Checklist Outline For Dental Radiographic Installations III-1. SYSTEM INFORMATION (See Section I-2) A. Installation 1. Date of survey 2. Room number 3. Department/Building 4. Institution 5. Unit identification number B. Generator 1. Manufacturer 2. Model type, model number, serial number 3. Maximum high voltage (kVp) 4. Maximum tu be current (mA) C. X-ray Tube Insert 1. Manufacturer 2. Model type 3. Serial number 4. Nominal focal spot sizes a. Large b. Small 5. Leakage technique factors D.
III-5. RADIATION BEAM RESTRICTORS A. Intraoral System (at least annually or after removal of cone) 1. X-ray field diameter at SSD B. Panoramic System (at lest annually or after removal or adjustment of slit diaphragm) 1. Slit size 2. Verticle alignment of slit 3. Horizontal alignment of slit C. Cephalometric System (at least annually or after removal or adjustment of diaphragm) 1. 8 x 10" (18 x 24 cm) receptor a. X-ray beam alignment b. X-ray field size 2. Other receptor size a. X-ray beam alignment b.
III-12. IDENTIFICATION OF PERSON CONDUCTING EVALUATION (See Section I-9) A. Name B. Title C. Professional Certification III-13. RECOMMENDATIONS AND SUGGESTIONS (See Section I-10) III-14. POSSIBLE ADDITIONS A. In-room Scatter Radiation (See Section IV-3) B. Protective Barrier/Shielding Survey (See Section IV-4) C. Leakage Radiation (See Section IV-2) D.
IV. Measurement of Area Radiation Levels IV-l. Introduction Parts I, II, and III, have concentrated on equipment In addition to these related radiation safety matters. concerns, a radiation survey of the facility should be performed. The following three types of radiation levels in the vicinity of the machine may be of interest: (a) Scattered radiation inside the examination room, (b) Stray radiation outside the examination room, (c) Leakage radiation from the x-ray tube housing.
(b) The lowest tube current station available on the control panel exceeds the maximum continuous rated current for the maximum rated tube potential, and (c) Dental x-ray tubes may have a specified duty cycle in addition to the maximum continuous rated tube current. If the ionization chamber cannot be positioned one meter from the source in certain radial directions the readings can be corrected using the inverse square law.
6) Select positions on the surface of an imaginary sphere of 1 meter radius with its-center located at the focal spot. Include points at a height equal to the plane including the tube housing and the collimator junction. 7) Measure the leakage radiation at the selected positions.
(b) Orientation of the x-ray beam in the room, (c) Workload of the x-ray unit, (d) Size of the room and the equipment layout, and (e) Degree of occupancy in the adjoining areas. One cannot arbitrarily assume that a given thickness of Lead will be appropriate on all barriers. Existing records of room barrier design and the report of the shielding evaluation should be reviewed. Any one of the following conditions should cause a new barrier evaluation to be Initiated.
following factors must be considered when quantitative measurements are completed: (a) Meter's energy response (b) Meter's directional response (c) Meter's intensity response (d) Ion chamber cross sectional area corrections (e) Meter's calibration (f) Meter's response time in the rate mode on its most sensitive scales. The selection and use of survey meters to measure low level radiation fields have been discussed in more detail in References #18 and #19.
Checklist Outline Measurement of Area Radiation Levels IV-2. LEAKAGE RADIATION (prior to first patient use or anytime damage to the tube housing is suspected) A. Measurement #l B. Measurement #2, etc. IV-3. IN-ROOM SCATTERED RADIATION MEASUREMENT (annually) A, Operator Position in Front of Table 1. Table upright 2. Table horizontal B. Head End of Table C. Foot End of Table D. Back Side of Table E. Location of Physiological Monitoring Equipment F. Other Occupied Locations in Room G.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. "Part 1020-Performance standards for Ionizing Radiation Emitting Products", 21 Code of Federal Regulations, Parts 800-1299 (1984). NCRP Report No. 33; "Medical X-ray and Gamma-RayProtection for Energies MeV," NCRP up to 10 Publications, P.O. Box 30175, Washington, D.C. 20014 (1968). W.R. Hendee and R.P. Rossi, "Quality Assurance for radiographic X-ray Units and Associated Equipment, HS Publication (FDA) 80-8094 Rockville, Maryland (1979) J.E.
Personal Communication with Thomas Mosely concerning FDA Compliance Policy Guide issued to manufacturers, assemblers, and field test personnel: "Measurement of Entrance Lateral Exposure Rate for Type Fluoroscopes-21 CFR 1020.32(d)" (1977). 14. P.P. Lin, "Acceptance Testing of Automatic Exposure Control Systems and Automatic Brightness Stabilized Fluoroscopic Equipment," pp 10-27, in AAPM Monograph No. 4.
