summary, mobile radiography allows for the diagnostic imaging of patients who are unable to be seen in the X-ray examination room. Therefore, mobile X-ray equipment is useful for patients who have difficulty with movement. However, staff are exposed to scattered radiation from the patient, and can receive potentially harmful radiation doses during radiography. The protection of staff is of utmost importance; therefore, we investigated the occupational radiation doses received by RTs, particularly eye doses, using phantom measurements. RTs can be located close to a patient (i.e., the source of scattered radiation) during mobile radiography. As eye doses can be significant, protective measures are essential for RTs. Protective aprons are important for protecting RTs, as is increasing the distance from the radiation source (i.e., the patient). Lead glasses may also be necessary for protecting the eyes of RTs. To reduce RT radiation exposure, RTs should remain distant from the patient if possible. However, because this distance may hinder verification of the patient’s condition, RTs sometimes work in close proximity to patients. This is a patient phantom study. In future, the data may need validation by comparison with personal RT dosimeter records. It is important to evaluate the radiation doses delivered to RTs during mobile radiography, as well as the scattered radiation distribution, to ensure adequate protection. Further comparison studies may be needed using the Monte Carlo method. radiographers and nurses have a responsibility to ensure that no one is within the radiation field during the X-ray exposure of the patient. This is achieved by informing all persons in the immediate area that an X-ray exposure is about to be made and asking them to stand a safe distance from the radiation field area. Shielding Placing a barrier of lead or concrete between the radiation source and an individual provides protection from X-radiation (Jones and Taylor, 2006; Ehrlich and Coakes, 2017). During mobile radiography, anyone assisting in an examination and staying in the radiation field should wear a lead-rubber apron or stand behind a mobile lead screen. Generally, walls in special care units where ionising radiation is used are designed to contain the radiation produced by the mobile X-ray tube within a set of criteria and limits determined by relevant legislation (Hart et al, 2002). Radiation protection during mobile radiography Nurses' understanding and adherence to radiation protection control measures during mobile radiography is of paramount importance in protecting patients, themselves and members of the public visiting the ward/unit. However, some research studies have found limited awareness and non-adherence to radiation protection control measures among nurses during mobile radiography (Anim-Sampong et al, 2015; Luntsi et al, 2016; Azimi et al, 2018). This can be attributed to a lack of radiation protection awareness programmes for nurses working

1. Dose Issues and
CT

2. Radiation
Radiation is the emission and
transmission of energy or particles of
matter from atoms that travels through
some material / through a vacuum1.
2 Types of Radiation
1. Particle Radiation (α & β
radiation)
2. Electromagnetic Radiation
(X and Gamma radiation)

3. Electromagnetic Radiation
http://www.mpoweruk.com/radio.htm

4. • Radiation Exposure: It describes the amount of radiation
traveling through the air. Many radiation monitors measure
exposure. The units for exposure are the roentgen (R)2 .
• Absorbed Dose: which describes the amount of radiation
energy deposited in the patient’s body as a result of
exposure. The units for absorbed dose are the radiation
absorbed dose (rad) and gray (Gy)2.
• Effective Dose: are calculated by calculating the
absorbed doses to individual organs weighted for their
radiation sensitivity.
• The radiation risk to the patient can be estimated from the
effective dose.
• The common unit to measure effective dose is the mSv 2.

5. Biological Effects of Radiation

6. Stochastic Effects:
• Stochastic effects are those that occur by chance
and consist primarily of cancer and genetic effects3.
• Stochastic effects often show up years after
exposure3.
• As the dose to an individual increases, the probability
that cancer or a genetic effect will occur also
increases3.
• There is no threshold dose below which it is
relatively certain that an adverse effect cannot occur
for Stochastic Effects 1.

7. Non Stochastic (Deterministic ) Effects:
• These are characterized by a threshold dose above
which they do occur (clear relationship between the
exposure and the effect)1.
• In addition; the magnitude of the effect is directly
proportional to the size of the dose4.
• Non stochastic effects typically result when very large
dosages of radiation are received in a short amount of
time4.
• Examples of non stochastic effects include erythema
(skin reddening), skin and tissue burns, cataract
formation, sterility, radiation sickness and death4.

8. CT’s Contribution
X-Ray Procedure Radiation
Dose
CT:
49%
Rest:
51%
Total X-Ray Procedures
CT:, 17,%
Rest:,
83,%

9. Estimated dosages of X-Ray
Procedures
Background radiation per annum ≈ 3mSv
1 CT Head ≈ 20 Skull X-ray Examinations
1 CT Abdomen/Pelvis (2 Phase Study) ≈ 32 Abdominal X-rays
1 CT Abdomen/Pelvis (Urogram) ≈ 60 Abdominal X-rays
1 CT Chest ≈ 70 Chest X-ray Examinations
Radiograph Effective Dose
(mSv)
DEXA Scan 0.001
Bite Wing Dental 0.004
Skull (AP&Lat) 0.1
Chest (AP&Lat) 0.1
Abdomen (AP) 0.7
T-Spine (AP&Lat) 1
L-Spine (AP&Lat) 1.5
CT Procedure Effective Dose
(mSv)
Head 2
Neck 3
Chest 7
Abdomen 8
Pelvis 6
T-Spine 6
Chest for PE 15
Coronary Angio 16

10. Factors to consider
4 Justification : Exam must be medically
• indicated.
5 Optimization: Do the least number of scans at the
lowest exposure .
6 Are non ionizing alternative better suited (MR
and Ultrasound)5.
1 Patient Age.
2 Patient Gender.
3 Patient size and weight.

11. CT Dose Descriptors
1. CT Dose Index (CTDIvol)
●This is the primary dose concept in MDCT measured
in milli Gray (mGy).
● It is directly displayed on the MDCT Scanner.
●CTDIvol (weighted average of dose across a single
slice) divided by a pitch factor.
●It can be used to directly compare
radiation dose from different scan
parameter settings.
But it doses not provide an accurate
dose to the patient and should not be used to
determine individual risk5.

12. CT Dose Descriptors
2. Dose Length Product (DLP)
●DLP is an indicator of the total dose for an entire CT
examination.
● DLP is determined by multiplying the CTDIvol value by
the scan length, (mGy-cm).
●DLP will change between patients due to differences
in their height and the resulting scan length.
●It also includes overscan (extra
Scanning from MDCT Scans).
●DLP alone is still not sufficient to
accurately asses the radiation risk to a patient
undergoing a MDCT scan5.

13. CT Dose Descriptors
3. Effective Dose (ED)
●ED reflects the radiation risk to the individual patient,
measured in milli Sievert (mSv).
●ED takes into account not only the amount of
radiation, but also the sensitivity of the tissue/organ
being radiated.
● ED = k x DLP
.
k is the weighting factor accounting for tissue
sensitivity.
●Still mathematical models to compute organ doses
are based on a standard adult (70kg) .
Thus ED estimation can underestimate the risk to
children/ thin patients and overestimate the risk to
obese patients5.

14. Factors Affecting Radiation Dose

15. 1.Tube Current (mA)
●Tube Current in CT implies the
amount of x-rays produced in the x-ray
tube.
●mA and mAs has a linear
relationship with respect to CT
radiation dose.
●When all other technical factors are kept the same, and mAs
are lowered , the radiation dosed is also lowered6.

16. Factors Affecting Radiation Dose
2. Peak Tube Voltage (kVp)
●This is the peak potential
difference between the anode
and cathode in the x-ray tube.
●It cause acceleration of the
electrons toward the anode to
produce x-rays.
● The most common range of kVps used in CT are 80 -140.
●The output of an x-ray tube is approximately proportional
to kVp2 . Therefore if kVp is doubled the radiation dose
increase by a factor of 4 5.

17. Factors Affecting Radiation Dose
3. Pitch
●Pitch is defined as the ratio of table feed per gantry
rotation to total x-ray beam with.
● Radiation doses is inversely
Proportional to the pitch.
● Therefore the greater the pitch
the lower the radiation dose to the patient and vise-versa.
●Protocols demanding high spatial resolution (e.g. Cardiac
ct scans) an pitch < 1 is used, translating in high radiation
doses to the patient5.

18. Factors Affecting Radiation Dose
4. Filters
●Consists of absorbent material inserted
between the x-ray tube and the patient .
● Filters absorb low energy x-rays and
“harden” the x-ray beam.
● Low energy x-rays contribute disproportionally to patient
radiation dose (especially to skin dose).
●Bow tie filters (often used in CT) deliver a uniform
intensity x-ray beam across the scanning object, resulting
in a more uniform distribution of the dose5.

19. Factors Affecting Radiation Dose
5. Patient Centering
●Patients normally have an elliptical cross-
Section( thinner in the periphery and
ticker in the centre.
● Bowtie filters are thicker in the periphery
and thinner in the centre, resulting in more x-rays reaching
the ticker central parts and less the thinner periphery.
● However for these filters to function properly the patient
must be centred at the gantry iso-center.
●If the patient is positioned off centred less x-rays pass
through the patient’s thicker central part ,resulting in more
noise in the centre of the images. While more x-rays reach
the peripheral portion of the body cross-section, increasing
unwanted radiation dose6.

20. Factors Affecting Radiation Dose
6. Repeats
●Multiple Scans results in an increase in
radiation dose to the patient .
● During a single visit to a CT suite, the
patient may be scanned multiple times.
● Patients can also undergo multiple ct scans within a
short period of time.
●How many of these scans are necessary and appropriate
Is the critical question that needs to be answered5.

21. Factors Affecting Radiation Dose
7. Dose efficiency (Geometric efficiency)
●In MDCT it is required that an equal number of x-ray
photons reach all active detectors.
●To ensure this a
certain amount of over-
beaming, beyond the
active detectors are needed (called the penumbra).
●This proportion of wasted radiation and subsequent dose
penalty is more profound with ct protocols using a thinner
detector configuration than those using a thicker one .
●The narrower the beam and the less the active detector
elements , the more radiation dose will increase5.

22. Factors Affecting Radiation Dose
8. Angular (X/Y) Dynamic Dose Modulation
●It modulates the x-ray tube current during the scan
according to the size of the scanned
object to provide.
●This is to provide optimal
penetration of the x-ray beam at a
specific tube angle for a specific
object.
●It provides the best dose saving for structure that are not
uniform in the x/y planes.
●Provide dose saving of approximately 10% for head
scans and 20-40% for chest scans6.

23. Factors Affecting Radiation Dose
9. Longitudinal (Z-axis) Dose Modulation
●It modulates the mAs along the longitudinal (Z) axis.
●Information for this modulation
are obtained from the surview
(scout) scan.
● It reduce dose in organs that have
lower attenuation(e.g: lungs) due
to the lower dose needed to obtain
diagnostic images.
●It also maintains an uniform image quality within the
scan5.

24. Factors Affecting Radiation Dose
10. Cardiac ECG Dose Modulation
● Retrospectively gated cardiac cta’s.
- Higher radiation dose to patient.
- More information that may be diagnostically relevant.
- Give functional information (e.g. Ventricular ejection fractions)
● Prospectively gated cardiac cta’s.
- Less radiation dose to patient (up to 83% less than retrospective studies).
- Loss of information that may be diagnostically relevant.
- No functional information (e.g. Ventricular ejection fractions)

25. Factors Affecting Radiation Dose
11. Paediatric Protocols
●The goal is to obtain a balance
between image quality and dose.
● These scan must be done with
the minimum mA that will still
provide a diagnostic relevant set of images.
● Low kVp settings in patients <45kg can result in 30-70%
dose reduction.
●Doubling the pitch from 1 to 2 will result in a 50%
decrease in the radiation dose.
●Paediatric examinations should also be performed with the
shortest possible scan time (0.5 ms or less) to minimize
patient movement and thus avoid repeating scan
procedures7.

26. Smart Card Protection for
Patients
●Up until a decade ago, radiation protection
was centred around protecting staff at
medical facilities.
●Patient protection was seen as not so
important, seen that their exposure to
radiation was thought to be only a few times in a life time.
●This notion has certainly change, and the radiation dose
patients received have become more prominent.
●What's needed is a way to track/record the radiation doses
an individual received from medical facilities over his
lifetime.
●To accomplish this the IAEA has launched a smart card

27. REFERENCES
1. Health Physics Society
. 2013. http://hps.org/publicinformation/ate/faqs/whatisradiation.html [2
June 2014].
2. United States Nuclear Regulatory Commission. 2013. http://www.nrc.gov/about-
nrc/radiation/health-effects/measuring-radiation.html [02 June 2014].
3. United States Environmental Protection Agency
. 2012.
http://www.epa.gov/rpdweb00/understand/health_effects.html [02 June 2014].
4. NDT Resource Center. 2013. https://www.nde-
ed.org/EducationResources/CommunityCollege/RadiationSafety/biological/nonstochastic/nonst
ochastic.htm [02 June 2014]
5. Mahesh, M. 2009. MDCT Physics: The Basics-Technology, Image Quality and Radiation Dose.
Philadelphia: Lippincott Williams & Wilkins.
6. Kalra, M.K., Saini, S. & Rubin, G.D. 2008. MDCT from Protocols to Practice. Milan, Italy:
Springer-Verslag Italia.
7. Siegal, M.J. 2007. Pediatric Body CT. 2nd ed. Philadelphia: Lippincott Williams & Wilkins.
8. International Atomic Energy Agency
.
http://www.iaea.org/Publications/Magazines/Bulletin/Bull502/50205813137.html [02 June 2014]

28. The End