Saturday, August 1, 2020

Radiation safety

Hi friends!!!

In our previous blog we have discussed about x ray machine working principle and components of x ray tube. Please check out for the link given below.

x ray machine working principle

components of x ray tube

In today's blog, we are going to discuss about radiation safety.

Excessive radiation dose may cause cancer induction, skin burns, genetic defects, sterility, cell killing etc. So radiation protection is a raising concern in radiology. Therefore, radiation safety is a important topic for healthcare professionals working in radiology as well as for the patients.

Let's get into the topic.


WHAT IS

RADIATION?

The radiation means energy in motion. There are two types of radiation Ionizing Radiation and Non Ionizing Radiation. Ionizing radiation has shorter wavelength, higher frequency and higher energy. Ionizing radiation have energy to eject orbital electrons. Example: x rays, gamma rays, beta rays.  Non ionizing radiation has longer wavelength, lower frequency and lower energy. Non ionizing radiation does not have energy to eject orbital electrons. Example: Ultraviolet light, lasers, radio waves, infrared light, microwaves.

The following image is the radiation warning symbol.

Image courtesy: Wikimedia commons
Licensed under: CC Share Alike 

WHAT ARE THE

TYPES OF

RADIATION

DOSES?


ABSORBED DOSE

Energy deposited in each tissue as a result of exposure to ionizing radiation. Absorbed dose is measured in mGy.

EQUIVALENT DOSE

Equivalent dose is a damaging properties of different types of radiation. Equivalent dose in milliSievert mSv = Absorbed dose in mGy.

EFFECTIVE DOSE

Effective dose specifies the long term effects of radiation exposure. It is measured in millisievert mSv. Factors include absorbed dose to all organs of the body, relative harm level of the radiation, sensitivities of each organ to radiation.


WHAT ARE THE WAYS TO

ACHIEVE RADIATION

SAFETY?


TIME DISTANCE SHIELDING

The radiation safety can be achieved by reducing the time of radiation exposure. Doubling the distance between patient and radiation source decreases the exposure by 4 times. Tripling the distance between patient and radiation source decreases the exposure by 4 times. Therefore increase in distance between patient and radiation source increases radiation safety.  Exposure varies inversely by the square of distance from the the x ray tube.

PROPER WORK PRACTICE

Proper work practice can improve  radiation safety to a great extent. It includes usage of TLD Badges. Scheduled preventive maintenance of the equipment. Handling by a qualified person. Usage of radiation safety accessories. The radiation protection materials include mobile protective barrier, lead apron, organ shielding.

EQUIPMENT TYPE APPROVAL

Usage of equipment type approved by AERB also contributes in  radiation safety. Obtain AERB permission prior to installation. Obtain license for operation.


WHAT ARE THE WAYS TO

LIMIT RADIATION I

RAYS?


BEAM REDUCING DEVICE

The usage of following devices limits radiation and improves  radiation safety in x ray machine.

APERTURE DIAPHRAGM

Aperture Diaphragm is a sheet of lead that comes with a circular, square or rectangular openings to restrict the x ray field size.


CONES

Cones are metal tubes that comes in different ranges of shapes and sizes. The length of the cone and size of the opening affects the x ray field size.

VARIABLE APERTURE

Variable apertures are lead plates or shutters which can be adjusted to change the size of the beam.

GRIDS

Grids are placed between patients and x ray film to reduce the scattered radiation reaching the detector, which greatly improves radiation safety. Grids are parallel strips made up of high attenuating material such as lead and interspace filled with low attenuating material such as carbon. Grid ratio is the ratio of height of lead strips to the distance between two lead strips.


NOTE: High mAs = High radiation dose, so keep mAs as low as possible. High kVp =low radiation dose. Here usage of high voltage increases radiation safety. Therefore, higher the voltage, shorter the wavelength. Here x rays will have greater penetrating power and greater intensity.


WHAT ARE THE WAYS TO

LIMIT RADIATION IN 

COMPUTED TOMOGRAPHY?

The following techniques can be used to improve  radiation safety in computed tomography.

TUBE CURRENT MODULATION

Automatic modulation of x ray tube current (mAs) based on rotational and longitudinal movement of patient through x ray beam reduces radiation dosage by 40-60%.

BOW TIE FILTER

Usage of Bow tie filter instead of conventional flat filters can limit lower energy x rays reaching the patient. Lower energy x rays does not contribute to image formation. But instead it increases a patient’s radiation dose. Using bow tie filter can reduce radiation dosage by 50%.

PITCH RATIO

The distance travelled by CT Table in one 360 degree gantry rotation divided by x ray beam width. For example, if a table travelled 10mm during one rotation and width of the x ray beam is 10mm, then the pitch is 10mm/10mm = 1mm.

Two fold increase in pitch, results in 50% reduction of radiation dose.


WHAT ARE THE RADIATION

PROTECTION 

ACCESSORIES?

The usage of following radiation protection materials improves  radiation safety to a great extent.

1. Mobile Protective Barrier (MPB)- 1.5 mm Lead Eqv.

2. Lead Aprons - 0.25 mm Lead Eqv.

3. Thyroid Shield -0.25 mm Lead Eqv.

4. Gonads Shield- 0.25 mm Lead Eqv.

5. Eye Wear (Shield)- 0.25 mm Lead Eqv.

6. Rubber hanging Flaps (In IR)-0.5 mm Lead Eqv. 

7. Hand Gloves -0.25 mm Lead Eqv.

8. Lead Glass window- 1.5 mm Lead Eqv. 

9. Door (Lead Lined)-1.7 mm Lead Eqv.

Image courtesy: Wikimedia commons
Licensed under: CC Share Alike 

Now I hope you have acquired some knowledge about radiation safety. We will discuss in detail about a topic related to Biomedical Engineering  in our next blog.

NOTE: Dear friends!!! ...Please do comment a topic related to Biomedical, so that we can discuss it in future blogs.


Check out for this blog about Computed Tomography

Generations of CT Scanners

COMPUTED TOMOGRAPHY|TECHNOLOGY|ARTIFACTS


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