Test examination

RPO THK-cbct

Tag one of the four alternatives (a, b, c or d) for each of the multiple-choice questions. Only one answer is correct. The open questions 21 till 24 are awarded the indicated maximal number of points if both derivation and answer are correct.

The examination is based on the syllabus Radiation Protection Officer - dental radiology, written by F. Pleiter, H.F. Boersma and A.A. Froma. You will find the correct answers here .

Complete the sentence corectly: The probability of the photo-electric effect to occur...
1. hardly depends on the photon energy
2. hardly depends on the atomic number of the material
3. increases if the photon energy becomes higher
4. increases if the atomic number of the material becomes larger
During X-ray diagnostics, the X-ray technicians wear personal protective clothing. Which of the following choices offers usually the best protection?
1. lead apron with a thickness of 0.25 lead-equivalent and a thyroid collar
2. lead apron with a thickness of 0.25 lead-equivalent without a thyroid collar
3. lead apron with a thickness of 0.35 lead-equivalent and a thyroid collar
4. lead apron with a thickness of 0.35 lead-equivalent without a thyroid collar
The tube voltage of an X-ray device is 70 kV. Each time an X-ray photo is taken, the dentist takes position behind a stone wall with a thickness of 10 cm, thus reducing his effective dose by a factor equal to the transmission of the wall. To answer the next question, you may use the transmission of X-radiation through stone (see Figure A ).
What is the transmission of the stone wall?
1. 0.000 01
2. 0.0001
3. 0.001
4. 0.01
Complete the sentence corectly: The tissue weighting factor w_T is used for the conversion from...
1. only equivalent dose to effective dose
2. only absorbed dose to equivalent dose
3. neither equivalent dose to effective dose nor absorbed dose to equivalent dose
4. both equivalent dose to effective dose and absorbed dose to equivalent dose
Two of the six salivary glands receive each an equivalent dose of 3 mSv while an intra-oral X-ray picture is taken by the dentist. The tissue weighting factor of the salivary glands is wsalivary = 0.01.
What is the contribution of this exposure to the effective dose received by the patient?
1. 0.01 mSv
2. 0.03 mSv
3. 1 mSv
4. 3 mSv
The grey shade describes the average brightness of a photo: an underexposed photo is too light and an overexposed photo is too dark.

The difference in grey shades of light and dark parts of an X-ray image is called contrast. If the contrast is extremely large, only the shades white and black show up. If the contrast is extremely small, the image shows only a single shade of grey.

Only one setting of the X-ray device is changed. The other settings remain the same.
In which way can one reduce the contrast of an X-ray photo?
1. by increasing the voltage across the X-ray tube
2. by decreasing the voltage across the X-ray tube
3. by increasing the current through the X-ray tube
4. by decreasing the current through the X-ray tube
To make a specific X-ray image, the extra filter is removed, so that only the intrinsic filter remains. Tube voltage and mAs value remain unchanged.
What is the consequence of this for an X ray image?
1. the average grey shade decreases
2. the skin dose decreases
3. the contrast increases
4. the contrast decreases
An X-ray picture turns out to be overexposed. Only one thing in the protocol is altered.
How can one ensure that the average grey shade of the next picture is smaller while the contrast remains the same?
1. by increasing the tube voltage
2. by reducing the tube current
3. by reducinge the length of the position indicating device
4. by reducing the opening of the position indicating device
The average effective dose in the Netherlands due to background radiation is about 4 μSv per day.
Complete the sentence corectly: Het risico hiervan is vergelijkbaar met het risico van...
1. 1 intra-oral photo or less
2. 1 - 100 intra-oral photos
3. 100 - 10 000 intra-oral photos
4. 10 000 intra-oral photos or more
What does the ALARA principle mean?
1. preference for any alternative method in which no ionizing radiation is applied
2. the received dose must be kept as low as reasonably achievable
3. the application must be justified, which means that the benefits outweigh the disadvantages
4. no dose limit shall be violated
According to the Decree on Basic Safety Standards Radiation Protection, which is the annual limit for the effective dose of an exposed category-A worker?
1. 100 μSv
2. 2 mSv
3. 20 mSv
4. 50 mSv
Does a risk inventory and evaluation (RI&E) always have to be carried out by the radiation protection officer?
1. yes
2. no, this may only be done by a registered radiation protection expert
3. no, this may only be done by radiation protection experts
4. no, this may in principle be done by everyone
There is no other X-ray device in the dental office besides a cone-beam CT-scanner.
Complete the sentence corectly: This cone-beam CT-scanner...
1. may be used without any restrictions
2. is subject to a license
3. may be used without a radiation protection officer
4. must be registered with the ANVS
According to the Regulation Basic Safety Standards Radiation Protection, a diagnostic X-ray device in the dental practice must be equipped with a position indicating device (PID).
What does one want to limit with the PID?
1. only the area exposed to the beam
2. only the distance between focus and skin
3. neither the area exposed to the beam nor the distance between focus and skin
4. both the area exposed to the beam and the distance between focus and skin
In order to comply with the specific justification for a cone-beam CT-scan, the oral surgeon asks his female patient about a possible pregnancy.
Complete the sentence corectly: In order to comply with the individual justification, this question is...
1. understandable, but was not necessary if it is irrelevant in the opinion of the oral surgeon
2. understandable, but may not be asked under the Decree on Basic Safety Standards Radiation Protection
3. in violation of the General Regulation on Data Protection (AVG)
4. justified because it must always been asked under the Decree on Basic Safety Standards Radiation Protection
A six month old child complains about sudden pain in the jaw. The mother brings the child to the clinic Oral and Maxillofacial Surgery where it is decided to take an OPT-recording of the jaw. Someone must keep the child on his or her lap.
Who is the first eligible?
1. the duty radiographer
2. the mother
3. a nurse practitioner
4. someone with a diploma Radiation Protection Officer
A clinical physicist must be involved in the acceptance test before a cone-beam CT scanner is put into use.
Complete the sentence corectly: The above statement is a regulation imposed by...
1. the Authority Nuclear Safety and Radiation Protection
2. the European Commission
3. the Regulation on Basic Safety Standards Radiation Protection
4. the Decree on Basic Safety Standards Radiation Protection
For a medical procedure, one often uses a diagnostic reference level (DRL).
Complete the sentence corectly: The DRL for cone-beam CT-scans is usually expressed in...
1. effective dose
2. entrance dose
3. product of entrance dose and irradiatied area of the body
4. product of entrance dose and length of the irradiated body part
Which measure leads to the largest dose rate reduction for the bystanders at otherwise constant settings?
1. increase the distance to the radiation source by a factor of 4
2. decrease the exposure time by a factor of 2 and also increase the distance to the radiation source by a factor of 2
3. decrease the exposure time by a factor of 4
4. decrease the field size (in cm²) by a factor of 2
A cone-beam CT scanner in a dental office is placed close to a window in the outside wall. The outer wall immediately forms the site boundary. To comply with the dose limit at the site boundary, the transmission of the window must be at least T = 0.2. The effective energy of the X-rays is 90 keV. To answer the next question, you may use the transmission of X-radiation through glass (see Figure B ).

What is the minimum thickness of the glass?

11 mm
17 mm
25 mm
40 mm

To answer questions 21 till 24, the full calculation must be given. Clearly indicate the calculation method and/or reasoning you use to arrive at the solution. Always state the quantities and units used.

Data for question 21
tube voltage	90 kV
filter	3 mm aluminum
yield of X-ray tube	zie figuur C
tube current	6 mA
exposure time	0.15 seconde
distance focus - skin	25 cm

An X-ray image is taken in the Oral Surgery department.

Calculate the patient's equivalent skin dose per X-ray photo.
(maximal 4 points)

Data for question 22
number of CBCT images per year	1200
average DAP value	800 mGy∙cm²
tube voltage	90 kV
thickness double glass	10 mm
transmission glass	see Figure B
distance patient - boundary of premises	1.5 meter

In the dental practice, the CBCT scanner is positioned right next to a double-glass window.

Calulate the annual effective dose at the boundary of the premises. If you fail to answer this question, you may assume 1 mSv.
Is this more or less than the dose limit at the boundary of the premises? Motivate your answer.

(maximal 5 points)

Data for question 23
tissue weighting factors	see Figure D
field size	18 cm × 10 cm
DAP value	1100 mGy·cm²
distance CBCT scanner - dental surgeon	3 meter
only thyroid, salivary glands and oral mucosa are hit by the direct beam
the contribution of scatter radiation to the effective dose of the patient may be neglected

A CBCT scan of the sinuses is made in the Oral Surgery department. During the recording, the treating dental surgeon stays in the room where the CBCT device is located.

Calculate the entrance dose (in mGy).
Estimate by means of a calculation the effective dose of the patient due to this scan.
Estimate the effective dose of the dental surgeon due to this scan.

(maximal 5 points)

Data for question 24
number of CBCT recordings per year	300
number of intraoral recordings per year	2000
tube voltage intra-oral device	70 kV
tube voltage CBCT scanner	90 kV
average DAP value CBCT scan	600 mGy·cm²
distance intraoral device - control console	2.5 meter
distance CBCT scanner - control console	1.5 meter
thickness plaster	12.5 mm
transmission plaster	see Figure E
both devices are always operated by the same person

In a practice room in which an intraoral device is already present, a cone-beam CT scanner is added. The control console is mounted on the outside of the room, next to that of the intraoral device. The wall between the control console and the practice room consists of plaster board.

Estimate the total annual effective dose of the operator of the intraoral device and the CBCT scanner by means of a calculation.
(maximal 6 points)

Last modified:23 December 2025 4.37 p.m.

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Test examination

To answer questions 21 till 24, the full calculation must be given. Clearly indicate the calculation method and/or reasoning you use to arrive at the solution. Always state the quantities and units used.

Data for question 21

Data for question 22

Data for question 23

Data for question 24