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  • Writer's pictureFrancesco Bruno Tagliaferro

Radiation protection (in Interventional Radiology)

What is Radiation Protection


Radiation protection is the discipline of the protection of humans beings and the environment from the harmful effects of ionizing radiation.


Historical background


Between the end of the 19th century and the beginning of the 20th century, the discoveries of Roentgen, Becquerel and the Curies paved the way for important research on ionizing radiation and their application in medicine, science and industry, but also led to awareness of the risks associated with exposure to such radiation and the importance of radiation protection.

Initially, the harmful effects of ionizing radiation were not known, and radiological procedures were performed without the necessary precautions. Around 1920, however, the immediate harmful effects of high doses of radiation became clear, while there was still no awareness of the delayed effects, which were more difficult to diagnose and link to radiation.

The concept of risk even at low doses or, better, of risk without a lower threshold but simply directly proportional to the dose, definitively established itself after the Second World War, when advanced experimentation on laboratory guinea pigs first and the effects resulting from the bombs of Hiroshima and Nagasaki then, they indicate the existence of correlations between low doses and non-reversible late effects.


General principles


The hypothesis of linearity without threshold is equivalent to admitting that every dose, however small, can lead to harmful, even serious, effects on the health of exposed individuals. This entails obvious and serious difficulties in identifying a universally acceptable dose limitation system. The dose limitation philosophy proposed by the ICRP and accepted by the main European and national regulations is based on two needs:


  • the prevention of deterministic effects;

  • the limitation of the probability of stochastic effects within values ​​considered acceptable.


To pursue the aforementioned objectives, the following three fundamental principles of radiation protection have been introduced:


  1. Justification: it establishes that the exposure of the individual and the population to additional doses of radiation is justifiable only if the benefits deriving from the practices that generate the additional doses are greater than the set of statistically foreseeable negative effects.

  2. Optimization: the optimization principle establishes that, if justified, the population's exposure must be kept as low as reasonably achievable (ALARA principle = As Low As Reasonably Achievable) also taking into account economic and social factors.

  3. Dose limitation: the principle of dose limitation states that individual doses, even if admissible on the basis of the principles of justification and optimization, must not however exceed specific limits determined in relation to the entire life on the basis of the coefficients risk ratings and in comparison with the risks accepted in conventional industry






Radiation protection involves a series of measures, including control of radiation sources, limitation of exposure time, protection of parts of the body not affected by the radiographic examination or procedure, reduction of radiation doses when possible and training of personnel involved in the use of ionizing radiation.

 

Radiation protection in interventional radiology


Interventional radiology procedures under fluoroscopic guidance are widely performed in Italy, and the number of procedures per year worldwide has increased over the last 20 years.

The increase in radiogenic exposure is invariably associated with an increased risk of radio-induced damage to the health of both operators and patients.

Radiation protection at work requires both appropriate education and training for interventional radiologists, as well as the availability of appropriate protective tools and equipment.

Professional radiation protection measures are necessary for all those working in the angiography room. This includes not only technicians and nurses, who spend a lot of time in a radiation environment, but also other professionals, such as anesthesiologists, who may only occasionally find themselves in a radiation environment.

All these professional figures, in addition to constant monitoring of the exposure dose and the use of adequate individual protection measures, should receive appropriate education and training on the risks related to radioexposure and on actions to reduce them.


Dose limits


Personnel working with ionizing radiation must be monitored to assess the extent of exposure. Healthcare workers exposed to radiation are monitored using three dosimeters, one for exposure of the hands, the other for the body and the third for the eyes.


Italian legislation, relating to ionizing radiation, divides workers into two categories: exposed and non-exposed workers. Exposed workers are, in turn, classified into category A or category B.


Exposed workers are those individuals who, due to the work carried out on behalf of the employer, are susceptible to radiation exposure exceeding any of the limits set for members of the public.


  • Category A exposed workers are those workers who carry out work that exposes them to the danger of ionizing radiation and who may receive a dose greater than 6 mSv per year. For these workers, physical and medical protection supervision must be ensured by a qualified expert and an authorized doctor through periodic visits at least every six months.

  • Category B exposed workers are those people who for work reasons may receive a dose between 1 mSv and 6 mSv per year.


Non-exposed workers are those people who may work in the vicinity of a Controlled Area but who cannot receive a dose higher than 1 mSv per year, i.e. the exposure limits for members of the public/population. The entire non-exposed population, including non-exposed workers, must receive a dose of less than 1 mSv per year.


Factors determining the dose in the angiography room

 

Patient-related factors

The main factor is represented by the weight of the patients: the greater the thickness to be crossed, the greater the attenuation of the radiation will be (and the smaller the quantity of radiation that reaches the detector). Therefore, the greater the thickness of the patient, the higher the input dose necessary to ensure adequate image quality, as the radiation required for sufficient penetration will increase exponentially.


Factors related to the angiography system

The quality and optimization of the angiography system contribute to dose containment.

An important element to consider is the type of system used: generally an angiography system optimized for one type of procedure is sub-optimal for another type of intervention. It is also necessary to consider the amount of "leakage radiation" which contributes, especially in older systems, to the radiation exposure of both the patient and the operator.




 

Factors related to the procedure

An extremely important procedural factor is the angle of the x-ray tube: the Antero-Posterior projection is recommended, when possible. Even small increases in tube angle are associated with significant dose increases.

Greater complexity of the procedure often translates into a dose increasing, due to the increase in its duration but also due to the use of different angles of the x-ray tube.

 

Radiation protection tools

 

In their daily practice, interventional radiologists use a series of dedicated screens that significantly reduce the scattered radiation coming from the patient.


There are three kinds of shields: structural shields, personal protective equipment, and additional shields placed on the patient.


The structural shielding essentially consists of the anti-X-ray glass suspended from the ceiling or mobile on wheels and the anti-X-ray bulkhead positioned under the angiographic table between the x-ray tube and the operator. These devices must always be used, as they have been shown to substantially reduce the dose to the operator. Unfortunately, they cannot be used if the X-ray tube-detector system is in an oblique or lateral position. Screens suspended from the ceiling, generally constructed of clear lead-containing plastic, should be used regardless of distance. The screens, correctly positioned, have proven to drastically reduce the dose to the operator's eyes.



Personal protective equipment includes aprons, thyroid collars, goggles, gloves and shielded headphones. Protective aprons and thyroid collars are the main radiation protection tool for interventional radiology operators: these should always be used.



 


Additional shields. Among the additional shields that can be used to block (or attenuate) the diffuse radiation coming from the patient are anti-X-ray sheets positioned directly on the patient's pelvis. The pelvis, due to the presence of large bones, is the main source of diffuse radiation coming from the patient and therefore by limiting or blocking this radiation it is possible to significantly reduce the exposure of operators.

 

Good practices for dose minimization

 

The reduction of the patient dose translates into a proportional reduction of the diffusion dose to the operator. Therefore, techniques that reduce patient dose generally also reduce occupational dose.


Minimize Fluoroscopy Time

Fluoroscopy should only be used to observe moving objects or structures. Review and the last image for the study, rather than perform a further fluoroscopic exposure.


Minimize the number of Fluorographic Images

For digital angiographic subtraction, variable “frame rates” tailored to the exam should be used. If available, use a stored fluoroscopy loop in place of a fluorographic acquisition if the image quality is sufficient to document the results.


Limit the use of magnifications

Modern angiography systems are equipped with electronic image enlargement (zoom) softwares. The use of these magnifications increases the radiation emitted by the angiography machine, thus increasing the radiation exposure to patients and operators. Generally the dose increase is exponential with the increase in magnification and as a general rule the dose increase is equal to the square of the ratio between the diameters of the magnification field. So if I move from a field of 20 to a field of 10, the dose increase is 4 times.


Use all available technologies for dose reduction

These include low dose fluoroscopic settings, low frame‐rate pulsed fluoroscopy, antiscatter grid removal, spectral beam filtration, etc.


Use good geometry for acquisitions

Position the patient support so that the patient is as far away from the x-ray tube as possible. Place the image receiver as close to the patient as possible.





Use collimation

Tightly adjust the collimating shutters to the area of ​​interest. Narrow collimation reduces patient dose and improves image quality by reducing dispersion.


Use all available information to plan the interventional procedure

When appropriate, use pre-procedural imaging (ultrasound, MRI, CT) to define the anatomy and pathology in question and to plan the interventional procedure, reducing the need for intraprocedural fluoroangiographic studies.


Stand in a low dispersion area

Stand as far away from the X-ray beam as possible. When using oblique or lateral projections, keep in mind that the maximum intensity of scattered radiation is located on the side of the patient from which the X-rays enter. When using these projections, the X-ray should be on the side opposite the operator whenever possible.





Use protective screens

When performing procedures with fluoroscopic guidance, you must wear a personal protective apron and a thyroid collar. Screens suspended from the ceiling are able to provide significant dose reduction, especially on unprotected areas of the head and neck. Glasses with leaded lenses are recommended if hanging screens cannot be used continuously during the entire procedure. Protection drapes under the table reduce the dose to the lower extremities substantially and should be used whenever possible.


Use appropriate fluoroscopic imaging equipment

Imaging systems that are optimized for one type of procedure or one part of the body may not be optimal for other types of procedures or other parts of the body. The use of fluoroscopic equipment in suboptimal conditions often results in a higher radiation dose. Fluoroscopic systems that incorporate dose reduction technologies are recommended.


Adopt correct radiation protection behavior in the cath lab

Such as using the x-rays only when the operator is actually seeing the monitor or avoiding placing the hands directly under the x-ray beam or avoid (unless strictly necessary) delivering x-rays while the nursing staff administers drugs in close proximity to the patient.


Wear dosimeters and know your radiation dose

The use of dose monitoring systems promotes procedural optimization in interventional radiology. Periodic monitoring of patient exposures for the different procedures provides information which, compared with relevant references (national LDRs or recommendations from scientific societies), allows the identification of technical and/or procedural changes for further optimization of exposures . Furthermore, constant monitoring allows you to periodically compare the activity of the operators of the same center for the same procedures and to implement corrective measures to reduce the procedural dose and align all operators with the "best practice".


Educate and instruct operators

This is the key point of radiation protection. Operators should be trained in all aspects of the dose optimization concepts and the ALARA (As Low As Reasonably Achievable) principles. This training must include:


  • the basic knowledge about ionizing radiation and radiation protection,

  • specific training on the equipment used and the related dose reduction systems,

  • the correct use of protection and dose measurement devices and verification of their availability in the cath lab,

  • the main technical and organizational prevention and protection measures that reduce radiation exposure.


Radiation protection means maximizing the clinical benefits of a procedure with respect to radio-induced damage, using dose reduction techniques whenever possible and taking into account that the dose delivered must be suitable for the medical purpose.




 

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