Radiation Protection in Mammography: Recommended Safety Procedures for the Use of Mammographic X-Ray Equipment - Safety Code 33

9. Procedures for minimizing dose to personnel

The guidelines and procedures outlined in this Section are primarily directed toward occupational radiation protection. Adherence to these will also, in many instances, provide protection to visitors and other individuals in the vicinity of a facility. The recommendations for safe work practices and procedures should be regarded as a minimum, to be augmented with additional requirements when warranted, to cover special circumstances in particular facilities.

To achieve optimum safety, radiology technologists must make every reasonable effort to keep irradiation of themselves and other personnel as far as practicable below the limits specified in Appendix I.

9.1 General recommendations

1. A room where mammographic X-ray examinations are done must not be used for more than one radiological investigation simultaneously.
2. Except for those persons whose presence is essential for the investigation, all other persons must leave the room when a mammographic X-ray examination is carried out.
3. Personnel must, at all times, keep as far away from the radiation beam as practicable. Radiation exposure of personnel by the primary X-ray beam must never be allowed unless the beam is adequately attenuated by protective screens or protective clothing. Deliberate irradiation of an individual for training purposes or equipment evaluation must never occur.
4. All personnel must take full advantage of available protective devices.
5. Operation of the X-ray tube shall be controlled from the control panel located behind a protective screen or inside a control booth. The technologist must be shielded when exposures are made.
6. If a patient escort or other person is called upon to assist, this person must be provided with protective clothing and be positioned so as to avoid the primary X-ray beam. No one must regularly perform these duties.
7. All technologists operating X-ray equipment and who are likely to receive a radiation dose in excess of 5 percent of the recommended dose limits for radiation workers specified in Appendix I, must wear personnel dosimeters.
8. All entrance doors to a mammographic X-ray room, including patient dressing room doors, must be kept closed while a patient is in the X-ray room. There should be a light or a sign on the outside of the patient dressing room indicating occupancy.
9. Powered-on mammographic X-ray equipment must not be left unattended.
10. Where radiation doses in excess of 5 percent of the recommended effective dose limits for radiation workers specified in Appendix I are regularly received by any one person, appropriate remedial steps must be taken to improve techniques and protective measures.
11. Mammographic X-ray equipment must be operated only by individuals who are properly trained for the equipment and the procedures being performed.
12. Technologists must have a clear view of the patient during every mammographic X-ray examination and must be able to communicate with the patient and/or attendants.

10. Procedures for minimizing dose to patients

The largest single contributor of man-made radiation exposure to the population is dental and medical diagnostic radiology. In total, such use of X-radiation accounts for more than 60 percent of the total man-made radiation dose to the general population.

The risk to the individual patient from a single radiographic examination is very low. However, the risk to a population is increased by increasing the frequency of radiographic examinations and by increasing the number of persons undergoing such examinations. For this reason, every effort should be made to reduce the number of radiographs and the number of persons examined radiographically, as well as to reduce the dose involved in a particular examination. In the case of mammographic screening programs, the benefit from the program must outweigh the risk from an increase of radiation dose to the group being targeted by the program.

To accomplish this reduction, it is essential that patients be subjected to only necessary radiological examinations and, when a radiological examination is required, it is essential that patients be protected from excessive irradiation during the examination.

The recommendations and procedures for the protection of the patient, outlined in this Section, are directed toward the physician, the radiologist and the technologist. They are intended to provide guidelines for elimination of unnecessary radiological examinations and for minimizing doses to patients when radiological examinations are indicated.

10.1 Guidelines for the prescription of diagnostic mammography

The medical practitioner is in a unique position to reduce unnecessary radiation dose to the patient by eliminating examinations which are not clinically justified. The practitioner can achieve this by adhering, as much as possible, to certain basic recommendations. These recommendations are presented below.

1. The request for a mammographic X-ray examination of a patient should be based on a clinical evaluation of the patient and should be for the purpose of obtaining diagnostic information.
2. It should be determined whether there have been any previous mammographic X-ray examinations which would make further examination unnecessary or allow for an abbreviated examination. The previous mammograms should be examined along with a clinical evaluation of the patient.
3. When a patient is transferred from one physician or hospital to another, any relevant mammograms or reports must accompany the patient and should be reviewed by the consulting practitioner.
4. When prescribing a mammographic X-ray examination, the physician should specify precisely the clinical indications and information required.
5. The number of mammographic views required in an examination must be kept to the minimum practicable, consistent with the clinical objectives of the examination.
6. In prescribing mammographic X-ray examinations of pregnant or possibly pregnant women, full consideration must be taken of the consequences of foetal irradiation. While it is generally accepted that the radiation dose to the ovaries and the foetus is low in mammography, the radiation beam should not irradiate the abdominal area.
7. In prescribing mammographic X-ray examinations of patients having breast implants, it should be noted that there may be a need for the use of special compression, positioning and loading techniques, and that the personnel of mammographic X-ray facility should be proficient in performing such procedure.
8. Repeat mammographic X-ray examinations should not be prescribed only because a mammogram may not be of the "best" diagnostic quality if the mammogram contains the required diagnostic information.
9. The quality of mammograms must be monitored routinely, through a Quality Assurance program, to ensure that they satisfy diagnostic requirements with minimal patient dose.
10. A patient's clinical records must include details of all mammographic X-ray examinations carried out.

10.2 Guidelines for screening mammography

In breast cancer screening programs, asymptomatic women undergo mammographic X-ray examinations with the goal to reduce breast cancer death by detecting cancer tumours at an early stage. In such programs, it is important to minimize participant exposure to radiation consistent with obtaining images of optimal diagnostic quality. Therefore, a mammography screening program should not be established unless mean glandular doses are within accepted limits and that a Quality Assurance program is implemented.

1. Selection of population groups for mammographic screening should be based on the concept that the benefit from the program should outweigh any risks from an increase of radiation dose to the group being targeted by the program.
2. Mammographic screening should not be done on pregnant or possibly pregnant women because of the consequences of foetal irradiation. The mammographic X-ray examination should be re-scheduled at a subsequent date.
3. Participants having breast implants should follow the same mammographic screening schedule as recommended forwomen without implants. However, for these participants, there may be a need for the use of special compression, positioning and loading techniques, and the personnel of mammographic X-ray facility should be proficient in performing such procedures.
4. The number of mammographic views required in an examination must be kept to the minimum practicable, consistent with screening program objectives.
5. Repeat mammographic X-ray examinations should not be prescribed only because a mammogram may not be of the "best" diagnostic quality if the mammogram contains the required diagnostic information.
6. The quality of mammograms must be monitored routinely, through a Quality Assurance program, to ensure that they satisfy diagnostic requirements with minimal patient dose.
7. For mobile mammography screening clinics, it is recommended that image processing be performed on site so that technologists can review their films which will reduce participant callbacks. However, since it is often difficult to stabilize film processors in mobile mammography screening clinics, additional care must be taken to ensure that image processing is optimized. In the situation where image processing cannot be optimized, batch processing at another location is acceptable.
8. Previous mammograms, including baseline mammograms, from screening mammography programs should be available to the radiologist for examination.

10.3 Guidelines for the carrying out of mammographic X-ray examinations

Next to elimination of unnecessary X-ray examinations, the most significant factor in reducing dose is ensuring that an examination is performed with good methodology and proper X-ray tube loading. It is possible, for example, to obtain a series of diagnostically acceptable mammograms and have the organ dose vary widely due to the choice of loading factors. It is the responsibility of the technologist, the medical physicist and the radiologist to be aware of this and to know howto carry out a mammographic X-ray examination with the lowest possible radiation exposure to the patient or breast screening participant.

The recommendations that follow are intended to provide guidance to the technologist, the medical physicist and radiologist in exercising their responsibility towards reduction of patient dose.

1. The mammographic X-ray system must be designed specifically for mammography and the image receptor must be compatible with the system.
2. A film-screen combination that provides good quality diagnostic results must be used. Direct exposure film must never be used in mammography.
3. Except in the case of mammography performed within a screening program, the technologist must not perform any examination which has not been prescribed by a physician responsible for the patient.
4. The dose to the patient must be kept to the lowest practicable value consistent with clinical objectives, and without loss of essential diagnostic information. To achieve this, techniques appropriate to the equipment available should be used and evaluated from time to time in terms of effectiveness.
5. Particular care in patient X-ray protection must be taken when mammographic X-ray examinations of pregnant or possibly pregnant women are carried out, even though the radiation dose to the abdomen and fetus are negligible during normal mammographic X-ray examinations.
6. There may be a need to use special procedures when performing mammographic X-ray examinations of patients with breast implants such as extra views, modified positioning, compression and loading techniques. Particular care of compression techniques must be taken since excessive compression of the implants during mammographic X-ray examination may cause rupture of the implant.
7. In mammography, it is recommended that the field normally be the full size of the image receptor, but not larger than the image receptor support, except at the chest wall. The amount of unexposed areas on the films should be minimal so to avoid the need for masking. Collimated-down views are useful in some purposes, but should be considered as a special procedure.
8. Appropriate compression must be used in all mammographic procedures.
9. Adequate X-ray beam filtration must be used in all mammographic procedures.
10. The technologist should use the maximum focal spot to skin distance consistent with good radiographic loading. For mammographic procedures, distances of less than 50 cm should not be used. For mammographic procedures including magnification, distances of less than 25 cm to the entrance surface of the breast shall not be used.
11. Full details of the mammographic procedures, including retakes, carried out should be noted on the patient's clinical records.
12. Irradiation times should be minimized to avoid unnecessary dose increase from reciprocity law failure and to avoid motion artifacts. This can be accomplished by the use of sufficiently high tube current values.
13. Cassettes should be loaded at least 30 minutes in advance to allow air to escape, and thus improving film/screen contact.
14. The technologist should examine the images after processing in order to verify that the techniques being used are producing diagnostic quality images and that the X-ray equipment is functioning correctly
15. An appropriate Quality Assurance program must be implemented on mammographic X-ray equipment and on film and Xerographic processing systems.
16. While recommended dose limits have been defined for radiation workers and the general population, there is no specific permissible level recommended for patients undergoing diagnostic X-rays procedures. However, it is possible to provide limits on the amount of radiation breast tissues receive by setting dose limits on the level of radiation a representative breast phantom would receives for a given irradiation. These dose limits are presented in Appendix II.
    
    For patients the risk involved with exposure to radiation must always be weighed against the medical requirement for accurate diagnosis. However, the dose to the patient should be kept as low as reasonably achievable.