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Therapeutic Radiographer practice questions

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Question 1Radiation Physics and Equipment

Which radiation quantity is defined as absorbed dose multiplied by a dimensionless radiation weighting factor for the type and energy of the radiation?

  1. Equivalent dose Correct answer.
  2. Exposure
  3. Absorbed dose
  4. Kerma

Explanation

Equivalent dose expresses stochastic risk by weighting absorbed dose for radiation quality, and its SI unit is the sievert. Absorbed dose alone does not account for differences in biological effectiveness between radiation types. Exposure and kerma describe ionisation in air and energy transferred to charged particles respectively.

Question 2Radiation Physics and Equipment

A photon beam delivers 2 Gy to tissue. Using a radiation weighting factor of 1 for photons, what is the equivalent dose?

  1. 1 Sv
  2. 2 Sv Correct answer.
  3. 20 Sv
  4. 0.2 Sv

Explanation

Equivalent dose equals absorbed dose multiplied by the radiation weighting factor, so 2 Gy times 1 gives 2 Sv. Photons have a weighting factor of unity, so the numerical value is unchanged while the unit changes from gray to sievert.

Question 3Radiation Physics and Equipment

In a linear accelerator, which component converts the low-energy RF drive into a high-power pulse delivered to the accelerating waveguide?

  1. The magnetron or klystron Correct answer.
  2. The flattening filter
  3. The ion chamber
  4. The bending magnet

Explanation

The RF power source, either a magnetron or a klystron, amplifies or generates the microwave power that is fed through the waveguide to accelerate electrons. The ion chamber monitors output, the flattening filter modifies the beam profile, and the bending magnet directs the electron beam.

Question 4Radiation Physics and Equipment

What is the primary purpose of the flattening filter in a conventional photon beam?

  1. To collimate the beam to the target volume
  2. To produce a more uniform dose profile across the treatment field Correct answer.
  3. To monitor the delivered dose
  4. To harden the beam by removing low-energy photons

Explanation

The flattening filter is a conical absorber placed in the beam that attenuates the forward-peaked photon fluence so the dose profile becomes approximately uniform across the field. It also causes some beam hardening, but that is a secondary effect rather than its purpose. Collimation and dose monitoring are performed by other components.

Question 5Radiation Physics and Equipment

Which interaction predominates for megavoltage photons in soft tissue and produces a scattered photon plus a recoil electron?

  1. Compton scattering Correct answer.
  2. Photoelectric absorption
  3. Pair production
  4. Rayleigh scattering

Explanation

In the megavoltage range and in low atomic number tissue, Compton scattering dominates because photon energies greatly exceed the binding energies of outer-shell electrons. The interaction yields a scattered photon and a recoil electron that deposits dose. Photoelectric absorption dominates at low energies and pair production requires at least 1.022 MeV and a high atomic number to be significant.

Question 6Radiation Physics and Equipment

Why is a high atomic number material such as tungsten used for the target in a medical linear accelerator?

  1. It is transparent to megavoltage electrons
  2. It provides high stopping power and efficient bremsstrahlung production Correct answer.
  3. It has a low melting point for easy cooling
  4. It minimises the production of scattered photons

Explanation

Bremsstrahlung yield increases with the atomic number of the target, so tungsten gives efficient conversion of electron energy into photons. Tungsten also has a high melting point and good thermal conductivity, which suits the high heat loads. Low atomic number materials would produce far fewer photons for the same electron current.

Question 7Radiation Physics and Equipment

What does the inverse square law state about photon fluence from a point source?

  1. It is inversely proportional to the distance from the source
  2. It is directly proportional to the distance from the source
  3. It is independent of distance from the source
  4. It is inversely proportional to the square of the distance from the source Correct answer.

Explanation

For a point source emitting isotropically, the same number of photons spread over an area that grows with the square of distance, so fluence falls as the inverse square of distance. Doubling the distance reduces fluence to one quarter. This underpins the use of inverse square corrections in dose calculations.

Question 8Radiation Physics and Equipment

Which device provides real-time verification of patient position using kilovoltage imaging or cone-beam CT immediately before treatment?

  1. Portal dose imaging detector
  2. Image-guided radiotherapy system Correct answer.
  3. Respiratory gating belt
  4. Electrometer

Explanation

Image-guided radiotherapy uses kV imaging, cone-beam CT, or similar modalities mounted on or near the treatment unit to confirm target and organ-at-risk position before delivery. Portal imaging verifies the megavoltage treatment field rather than providing soft-tissue localisation. Gating belts and electrometers serve different purposes.

Question 9Radiation Physics and Equipment

A photon beam has a percentage depth dose of 67% at 10 cm depth for a 10 x 10 cm field at 100 cm source-surface distance. What absolute dose is delivered at 10 cm if the dose at dmax is 2.4 Gy?

  1. 0.67 Gy
  2. 2.40 Gy
  3. 1.61 Gy Correct answer.
  4. 3.58 Gy

Explanation

The dose at depth equals the dose at dmax multiplied by the percentage depth dose expressed as a fraction, so 2.4 Gy times 0.67 gives approximately 1.61 Gy. Percentage depth dose describes the fall in dose with depth relative to the maximum.

Question 10Radiation Physics and Equipment

A treatment is prescribed 60 Gy in 30 fractions. Using the linear-quadratic model with an alpha/beta ratio of 10 Gy for tumour, what is the biologically effective dose?

  1. 60 Gy
  2. 90 Gy
  3. 120 Gy
  4. 72 Gy Correct answer.

Explanation

The biologically effective dose equals total dose multiplied by (1 + dose per fraction divided by alpha/beta). Each fraction is 2 Gy, so the factor is 1.2 and 60 Gy times 1.2 gives 72 Gy. This quantity is used to compare fractionation schedules.

Question 11Radiation Physics and Equipment

Which statement correctly describes the difference between source-surface distance and source-axis distance?

  1. Source-axis distance is measured to the isocentre, whereas source-surface distance is measured to the patient skin surface Correct answer.
  2. Source-surface distance is always larger than source-axis distance
  3. Source-axis distance applies only to electron beams
  4. Source-surface distance is measured from the detector to the patient

Explanation

Source-axis distance is a fixed machine parameter measured from the source to the axis of gantry rotation, typically 100 cm on modern linacs. Source-surface distance varies with patient anatomy and set-up because it is measured to the skin surface. Output calibration and dose calculations may reference either.

Question 12Radiation Physics and Equipment

In electron beam therapy, why does dose fall rapidly beyond a certain depth?

  1. Electrons are attenuated only by the inverse square law
  2. Electrons undergo pair production in tissue
  3. Electrons have a higher radiation weighting factor than photons
  4. Electrons have a finite range determined by their energy and are stopped by multiple scattering and ionisation Correct answer.

Explanation

Electrons lose energy continuously through inelastic collisions and scattering until they reach their maximum range, beyond which dose falls sharply. This steep distal fall-off allows sparing of tissue deep to the target. The practical range increases with beam energy.

Question 13Radiation Physics and Equipment

A patient is treated at 90 cm source-surface distance instead of the calibrated 100 cm. Ignoring other corrections, how does the dose rate at the surface change?

  1. It increases by a factor of about 0.90
  2. It remains unchanged
  3. It increases by a factor of about 1.23 Correct answer.
  4. It decreases by a factor of about 0.81

Explanation

By the inverse square law the dose rate scales as the square of the ratio of distances, so (100/90) squared equals approximately 1.23. Moving the patient closer to the source increases the dose rate. The correction must be applied whenever the treatment distance differs from calibration.

Question 14Radiation Physics and Equipment

Which collimator setting defines the field size at the isocentre for a photon beam on a modern linear accelerator?

  1. The jaws and multileaf collimator projected to the isocentre plane Correct answer.
  2. The source-to-diode distance
  3. The electron gun filament current
  4. The flattening filter diameter

Explanation

Field size is set by the secondary collimators, namely the jaws and the multileaf collimator, whose positions are calibrated to project a defined field at the isocentre. The flattening filter is a fixed component and does not define field size. Filament current controls electron emission rather than collimation.

Question 15Radiation Physics and Equipment

What is the main advantage of using a multileaf collimator for conformal radiotherapy?

  1. It shapes the field to the target projection from each gantry angle without manufacturing custom blocks Correct answer.
  2. It increases the beam energy to improve penetration
  3. It eliminates the need for dose calibration
  4. It removes the need for patient immobilisation

Explanation

A multileaf collimator uses independently positioned leaves to create fields conforming to the target projection, and it can be reconfigured between beams or during arcs. This avoids the labour of casting and mounting custom blocks. It does not change beam energy or remove the need for calibration and immobilisation.

Question 16Radiation Physics and Equipment

Which quantity describes the ratio of absorbed dose at a given depth in a phantom to the dose at the same point in free space, and is used in dose calculations?

  1. Percentage depth dose
  2. Inverse square factor
  3. Tissue-air ratio Correct answer.
  4. Backscatter factor

Explanation

Tissue-air ratio compares dose at a point in a phantom with the dose that would occur at the same point in air, removing the effect of distance so it can be applied at any source-surface distance. It is used in isocentric dose calculations and in the scatter-maximum ratio family. Percentage depth dose includes distance effects.

Question 17Radiation Physics and Equipment

During commissioning, a farmer-type ionisation chamber is used to measure absorbed dose to water. Which factor corrects the chamber reading for the difference between the calibration beam quality and the user beam quality?

  1. The temperature-pressure correction factor
  2. The beam quality correction factor Correct answer.
  3. The recombination correction factor
  4. The polarity correction factor

Explanation

The beam quality correction factor accounts for the change in chamber response when the user beam quality differs from that of the calibration beam. Polarity, recombination, and temperature-pressure corrections address measurement conditions rather than beam quality. All these factors are applied to convert the corrected reading into absorbed dose to water.

Question 18Radiation Physics and Equipment

A patient receives 2 Gy per fraction but the tumour alpha/beta ratio is 3 Gy. What is the biologically effective dose for a single fraction?

  1. 2 Gy
  2. 0.67 Gy
  3. 3.33 Gy Correct answer.
  4. 6 Gy

Explanation

The biologically effective dose for one fraction is dose multiplied by (1 + dose divided by alpha/beta), giving 2 times (1 + 2/3), which equals 3.33 Gy. A low alpha/beta ratio means the tissue is more sensitive to fraction size, so the biologically effective dose per gray is higher.

Question 19Radiation Physics and Equipment

Which statement best explains why a photon beam has a build-up region near the surface?

  1. Photons are absorbed completely within the first millimetre of tissue
  2. Secondary electrons set in motion reach an equilibrium fluence only after travelling a finite distance Correct answer.
  3. The beam energy decreases with depth
  4. The collimator scatters photons back towards the surface

Explanation

At the surface few secondary electrons are produced ahead of the point, so dose is low; with depth the electron fluence builds towards charged-particle equilibrium and dose reaches a maximum at dmax. The depth of maximum dose increases with beam energy. Beyond dmax, attenuation of photons causes the dose to fall.

Question 20Radiation Physics and Equipment

A 6 MV photon beam has a tissue-maximum ratio of 0.78 at 10 cm depth for a 10 x 10 cm field. If the dose at dmax at the isocentre is 2 Gy, what is the dose at 10 cm?

  1. 1.28 Gy
  2. 1.56 Gy Correct answer.
  3. 2.56 Gy
  4. 0.78 Gy

Explanation

In an isocentric calculation the dose at depth equals the dose at dmax multiplied by the tissue-maximum ratio, so 2 Gy times 0.78 gives 1.56 Gy. Tissue-maximum ratios are independent of source-surface distance, making them convenient for isocentric techniques.

Question 21Radiation Physics and Equipment

What is the purpose of a wedge filter in photon radiotherapy?

  1. To reduce the penumbra width
  2. To monitor the delivered dose
  3. To increase the beam energy
  4. To produce a graduated dose profile across the field to compensate for sloping surfaces or improve homogeneity Correct answer.

Explanation

A wedge attenuates the beam differentially across its width, tilting the isodose curves so that dose can be redistributed within the patient. This compensates for missing tissue or sloping surfaces and can improve dose homogeneity in combination with opposing fields. It does not alter beam energy or monitor dose.

Question 22Radiation Physics and Equipment

A dose calculation shows that 100 monitor units deliver 1 Gy at dmax for a reference field. How many monitor units are required to deliver 2.5 Gy at dmax under the same conditions?

  1. 250 monitor units Correct answer.
  2. 40 monitor units
  3. 100 monitor units
  4. 2.5 monitor units

Explanation

Output is proportional to monitor units, so the required monitor units equal the desired dose divided by the dose per monitor unit, giving 2.5 divided by 0.01, which is 250. Monitor units are the machine's calibrated measure of delivered output.

Question 23Radiation Physics and Equipment

In a flattening-filter-free photon beam, which characteristic is most typical compared with a flattened beam?

  1. A steeper distal fall-off resembling an electron beam
  2. A reduced need for image guidance
  3. A higher dose rate with a peaked central profile and different out-of-field dose characteristics Correct answer.
  4. A lower dose rate with a perfectly uniform profile

Explanation

Removing the flattening filter raises the dose rate substantially and leaves a forward-peaked profile, which is exploited in techniques such as stereotactic and volumetric arc treatments. Out-of-field dose and surface dose also change because the filter is no longer present to attenuate and scatter. Image guidance requirements are not reduced.

Question 24Radiation Physics and Equipment

A treatment plan uses two opposed fields with a wedge. Which combination of wedge orientations produces a homogeneous dose distribution across the target?

  1. Both wedges should be removed to avoid inhomogeneity
  2. Both wedges should have their thick ends on the same side
  3. Only one field should be wedged
  4. The wedges should be oriented with their thick ends opposed across the patient Correct answer.

Explanation

With opposed wedged fields the wedges are arranged so that their thick ends point in opposite directions, which balances the tilted dose distributions and produces a more uniform combined dose. Placing thick ends on the same side would add the tilts and worsen homogeneity. Wedge orientation must be planned carefully for each beam arrangement.

Question 25Radiation Physics and Equipment

Why must a correction be applied for ion recombination when calibrating a linac with high dose per pulse?

  1. Some ion pairs recombine before collection, so the measured charge underestimates the true dose Correct answer.
  2. The electrometer gain drifts with temperature
  3. The beam energy increases at high dose rate
  4. The chamber volume changes with dose rate

Explanation

At high dose per pulse, the density of ions in the chamber cavity is high and a fraction recombines before reaching the collecting electrode, reducing the measured charge. The recombination correction factor compensates for this loss. It is determined by measuring the chamber response at two voltages and extrapolating.

Question 26Radiation Physics and Equipment

On a medical linear accelerator, what is the primary role of the bending magnet system in the beam transport line?

  1. To deflect the accelerated electron beam through a defined angle and direct it toward the target or exit window Correct answer.
  2. To monitor the delivered dose and terminate the beam when the set monitor units are reached
  3. To accelerate electrons between successive drift tubes using a radiofrequency field
  4. To focus the electron beam onto the target and remove off-energy particles

Explanation

The bending magnet (or achromatic bend system) takes the high-energy electron beam leaving the accelerating waveguide and turns it through a fixed angle so it exits along the treatment axis. Energy-defining slits and focusing elements are associated with this transport, but the defining function of the bend itself is angular deflection of the beam.

Question 27Radiation Physics and Equipment

A photon beam is calibrated so that 1 monitor unit delivers 1 cGy at dmax under reference conditions. A plan requires 180 cGy at dmax from a single field. How many monitor units must be set?

  1. 180 MU Correct answer.
  2. 18 MU
  3. 1800 MU
  4. 1.8 MU

Explanation

If each monitor unit corresponds to 1 cGy at dmax, then the number of monitor units equals the required dose in cGy. A requirement of 180 cGy therefore needs 180 MU. This direct proportionality holds only when the field, depth and geometry match the calibration conditions.

Question 28Radiation Physics and Equipment

A 6 MV photon beam has a percentage depth dose of 67% at 10 cm depth for a 10 x 10 cm field at 100 cm SSD. If the dose at dmax is 2 Gy, what is the approximate absorbed dose at 10 cm depth?

  1. 1.34 Gy Correct answer.
  2. 0.67 Gy
  3. 2.00 Gy
  4. 2.99 Gy

Explanation

Percentage depth dose expresses the dose at depth as a percentage of the dose at dmax along the same central axis. Multiplying 2 Gy by 0.67 gives approximately 1.34 Gy at 10 cm. The value must be lower than the dmax dose because attenuation and inverse-square effects dominate beyond dmax.

Question 29Radiation Physics and Equipment

A VMAT plan is delivered with the gantry rotating continuously while the multileaf collimator and dose rate vary. Which quality assurance measurement most directly verifies that the delivered dose distribution matches the planned distribution in a patient-like geometry?

  1. Checking the mechanical isocentre coincidence of the gantry, collimator and couch axes
  2. Verifying the flatness and symmetry of the photon beam at a fixed gantry angle
  3. Measuring the output constancy of the photon beam with a reference ionisation chamber at dmax
  4. Comparing the planned and measured dose distribution using a detector array in a phantom with the actual gantry angles Correct answer.

Explanation

Patient-specific pre-treatment verification compares the calculated three-dimensional dose with a measurement made under the same dynamic delivery conditions, typically using a detector array or film in a phantom. This captures the combined effect of leaf motion, gantry rotation and dose-rate modulation. Mechanical and beam-constancy tests are necessary but do not verify the individual plan.

Question 30Radiation Physics and Equipment

During acceptance testing, the measured penumbra of a photon beam is wider than the manufacturer's specification. Which combination of factors most plausibly explains this finding?

  1. A lower photon beam energy combined with a decreased source-to-surface distance
  2. A mis-set collimator rotation combined with an incorrect field size at the isocentre
  3. A higher dose rate combined with a shorter pulse duration from the linear accelerator
  4. A larger focal spot size combined with increased lateral scatter in the phantom at the measurement depth Correct answer.

Explanation

Penumbra arises from the finite size of the focal spot, lateral scatter of photons and electrons in the medium, and geometric divergence of the collimated beam. A larger focal spot and greater lateral scatter both broaden the dose gradient at the field edge, widening the measured penumbra. Dose rate and pulse duration do not directly determine penumbal width.

Question 31Radiation Protection and Safety

Under the ALARA principle as applied to a therapeutic radiographer, which action best reflects optimisation of protection for staff during a high-dose-rate brachytherapy procedure?

  1. Maximising distance and minimising time near the source while using shielding Correct answer.
  2. Relying solely on the prescribed dose to the patient to determine staff safety
  3. Rotating staff so each person receives the same annual dose
  4. Increasing the number of staff present to share the workload

Explanation

ALARA requires that doses be kept as low as reasonably achievable, taking economic and social factors into account. For a radiographer this is achieved through the classic triad of time, distance and shielding. Maximising distance and minimising time near a high-activity source, together with shielding, reduces staff dose without compromising patient treatment.

Question 32Radiation Protection and Safety

Which quantity is used in radiation protection to express the equivalent dose to an organ, taking account of the type of radiation?

  1. Kerma in air
  2. Exposure in roentgen
  3. Absorbed dose in gray
  4. Equivalent dose in sievert Correct answer.

Explanation

Equivalent dose is the absorbed dose averaged over a tissue or organ, weighted by the radiation weighting factor for the type and energy of radiation. It is expressed in sieverts. Absorbed dose in gray does not account for radiation type, and kerma and exposure are physical quantities not used for protection dose limits.

Question 33Radiation Protection and Safety

A therapeutic radiographer wears a whole-body personal dosemeter and a separate extremity dosemeter. Where should the whole-body dosemeter normally be worn when no lead apron is used?

  1. Clipped to the collar over a lead apron
  2. Under the lead apron at waist level
  3. On the trunk at chest or waist level, outside clothing Correct answer.
  4. On the wrist of the dominant hand

Explanation

When no protective apron is worn, the whole-body dosemeter is worn on the trunk, typically at chest or waist level, outside clothing so it samples the dose to the body. It must not be shielded by an apron, because that would underestimate the body dose. Extremity dosemeters are worn separately on the hand or wrist.

Question 34Radiation Protection and Safety

In a controlled area around a linear accelerator, which sign and access arrangement is required?

  1. A fire exit sign with unrestricted public access
  2. A general notice permitting staff and visitors free access
  3. A first-aid sign with access for all hospital staff
  4. A warning sign with restricted access limited to authorised persons Correct answer.

Explanation

A controlled area is one where access is restricted for radiation protection purposes and where occupational exposure conditions are kept under review. It must be clearly demarcated and signed with the radiation warning symbol, and entry is limited to authorised persons who have been given local rules and instruction. Free or unrestricted access would defeat the purpose of area classification.

Question 35Radiation Protection and Safety

Which principle of the international system of radiological protection applies specifically to the planned exposure situation of treating a patient with radiotherapy?

  1. Collective dose constraint, so the population dose is minimised
  2. Authorisation, so each fraction requires a new licence
  3. Dose limitation, so the patient dose never exceeds a fixed annual cap
  4. Justification, so that the benefit to the patient outweighs the detriment Correct answer.

Explanation

In medical exposure, the principle of justification requires that the individual patient's benefit from the exposure outweighs the associated detriment. Dose limits do not apply to patients receiving radiotherapy, because the exposure is deliberate and clinically indicated. Constraints and optimisation apply to staff and public exposure, not to the therapeutic dose delivered to the patient.

Question 36Radiation Protection and Safety

A radiographer must handle a sealed source with a dose rate of 4 mSv/h at 1 m. Using the inverse square law, what is the approximate dose rate at 2 m?

  1. 4 mSv/h
  2. 2 mSv/h
  3. 8 mSv/h
  4. 1 mSv/h Correct answer.

Explanation

The inverse square law states that dose rate is inversely proportional to the square of the distance from a point source. Doubling the distance from 1 m to 2 m reduces the dose rate by a factor of four, so 4 mSv/h becomes approximately 1 mSv/h. This principle underpins the emphasis on distance in radiation protection.

Question 37Radiation Protection and Safety

Which document typically sets out the local rules for safe working in a radiotherapy department?

  1. The manufacturer's service manual
  2. The patient information leaflet
  3. The local rules approved by the radiation protection adviser and employer Correct answer.
  4. The departmental holiday rota

Explanation

Local rules are written instructions that translate the employer's radiation protection arrangements into practical working procedures for a defined area. They are drawn up with advice from the radiation protection adviser and approved by the employer, and they cover access, dosimetry, equipment checks and emergency procedures. They are not patient information or equipment documentation.

Question 38Radiation Protection and Safety

A radiographer is planning a treatment room layout to reduce occupational dose. Which combination best applies the principles of time, distance and shielding?

  1. Increasing the source-to-staff distance and using a mobile lead shield Correct answer.
  2. Standing close to the gantry to monitor the patient continuously
  3. Shortening the treatment time by removing beam-stopping devices
  4. Reducing the number of wall shields to improve visibility

Explanation

Occupational dose is reduced by increasing distance from the source, minimising the time spent in the radiation field and placing shielding between the source and the person. Combining distance with a mobile lead shield addresses two of these factors directly. Standing close or removing shielding increases dose.

Question 39Radiation Protection and Safety

During a fluoroscopic procedure in a radiotherapy planning suite, a radiographer wears a lead apron of 0.35 mm lead equivalent. What is the main purpose of this apron?

  1. To reduce the primary beam energy reaching the detector
  2. To protect the patient from the treatment beam
  3. To attenuate scattered radiation reaching the wearer's trunk Correct answer.
  4. To replace the need for a personal dosemeter

Explanation

A lead apron is personal protective equipment that attenuates scatter radiation before it reaches the wearer's body, reducing occupational dose to the trunk. It does not protect the patient and does not remove the requirement for dosimetry. Aprons are not used to modify the primary beam energy.

Question 40Radiation Protection and Safety

Which statement correctly describes the role of a radiation protection adviser (RPA) in a radiotherapy department?

  1. They provide expert advice on compliance with radiation protection legislation and local arrangements. Correct answer.
  2. They prescribe the radiotherapy dose for each patient.
  3. They operate the linear accelerator during treatment delivery.
  4. They authorise annual leave for radiographers.

Explanation

The radiation protection adviser is appointed to give expert advice on radiation protection, including compliance with legislation, local rules, shielding design and accident investigation. The role is advisory and does not include prescribing treatment or operating equipment. Staff management is not part of the RPA function.

Question 41Radiation Protection and Safety

A radiographer's whole-body dosemeter records 6 mSv over a two-month period. Which action is most appropriate under a typical monitoring programme?

  1. Discard the dosemeter and issue a new one without recording the result
  2. Ignore the result because it is below any investigation level
  3. Immediately suspend the radiographer from all work with radiation
  4. Record and review the dose and investigate if it exceeds the local investigation level Correct answer.

Explanation

Doses are recorded and reviewed against investigation levels set locally. If a result exceeds the investigation level, an investigation is triggered to identify the cause and take corrective action. Results are not discarded, and suspension is not automatic unless a dose limit has been exceeded or there is a serious concern.

Question 42Radiation Protection and Safety

In a radiotherapy department, which area would typically be classified as a supervised area rather than a controlled area?

  1. The linear accelerator control console during treatment
  2. Inside the treatment room during beam-on
  3. The brachytherapy source storage room
  4. A corridor adjacent to the treatment room where dose rates are low but above background Correct answer.

Explanation

A supervised area is one where occupational exposure conditions are kept under review but where the dose rate is low enough that access need not be restricted. A corridor with low but measurable dose rates fits this description. The treatment room, control console and source store are controlled areas because of higher dose rates or restricted access requirements.

Question 43Radiation Protection and Safety

Which of the following is the most appropriate way to reduce the dose to the lens of the eye for a radiographer working near scatter radiation?

  1. Removing the lead apron to improve mobility
  2. Wearing lead glasses and using a ceiling-suspended shield Correct answer.
  3. Wearing a second whole-body dosemeter
  4. Increasing the time spent in the scatter field

Explanation

The lens of the eye is sensitive to radiation, and protection is achieved by shielding the head with lead glasses and using a ceiling-suspended screen to intercept scatter before it reaches the face. Additional dosemeters measure dose but do not reduce it. Increasing time in the field or removing aprons increases exposure.

Question 44Radiation Protection and Safety

A patient is treated with a high-energy photon beam. Which statement about neutron production and protection is correct?

  1. Neutrons are produced above approximately 10 MV and require additional shielding considerations Correct answer.
  2. Neutrons are not a radiation protection concern in radiotherapy
  3. Neutrons are produced only by kilovoltage beams
  4. Neutrons are fully stopped by a standard lead apron

Explanation

Above approximately 10 MV, photon beams can produce photoneutrons in high-Z materials in the accelerator head. This requires consideration of additional shielding, particularly for the maze and door, and may influence dosimetry. Kilovoltage beams do not produce significant neutrons, and a lead apron is not designed to stop neutrons.

Question 45Radiation Protection and Safety

A radiographer is asked to justify the use of a lead shield for a staff member standing behind a mobile barrier during a procedure. Which reasoning is most consistent with protection principles?

  1. The barrier increases the primary beam output
  2. The barrier replaces the need for area monitoring
  3. The barrier is unnecessary because dose limits do not apply to staff
  4. The barrier reduces scatter dose, supporting optimisation of protection Correct answer.

Explanation

Shielding reduces the dose received by staff and is a practical application of optimisation. Dose limits do apply to staff, so the barrier is not unnecessary. A barrier does not change the primary beam output and does not remove the need for area monitoring to confirm dose rates.

Question 46Radiation Protection and Safety

Which statement about the dose limit for occupational exposure of the whole body under the international system is correct?

  1. 5 mSv per year with no averaging
  2. 20 mSv per year averaged over five years, with no more than 50 mSv in any single year Correct answer.
  3. 50 mSv per year averaged over five years, with no more than 20 mSv in any single year
  4. 100 mSv per year with no averaging

Explanation

The international system sets an effective dose limit for occupational exposure of 20 mSv per year averaged over five consecutive years, with the effective dose not exceeding 50 mSv in any single year. This provides flexibility while controlling cumulative risk. The other combinations invert or misstate the values.

Question 47Radiation Protection and Safety

A radiographer notices that the door interlock on a treatment room fails to prevent beam-on when the door is open. What is the most appropriate immediate action?

  1. Stop treatment, make the area safe and report the fault immediately Correct answer.
  2. Continue treatment and report the fault at the end of the day
  3. Increase the dose rate to shorten the treatment
  4. Ask the patient to hold the door closed during treatment

Explanation

A failed door interlock is a serious safety fault that could allow exposure of persons entering the room. Treatment must stop, the area must be made safe and the fault reported immediately so that the equipment is taken out of service and repaired. Continuing treatment or improvising with the patient would expose people to risk.

Question 48Radiation Protection and Safety

Which of the following best describes the purpose of a dose constraint in the context of public exposure from a radiotherapy facility?

  1. To define the dose that must be delivered to the tumour
  2. To specify the dose at which staff must be suspended
  3. To set a maximum value for the dose to the public from the facility that is below the legal limit Correct answer.
  4. To replace the need for shielding calculations

Explanation

A dose constraint is a prospective restriction on the dose to the public from a planned source, set below the legal dose limit to ensure that the limit is not approached. It is a planning tool used in shielding design and optimisation. It does not relate to tumour dose or staff suspension and does not remove the need for shielding calculations.

Question 49Radiation Protection and Safety

A radiographer is reviewing a shielding calculation for a new linear accelerator room. Which factor is most important to include when estimating the dose at the boundary of the controlled area?

  1. The brand of the treatment couch
  2. The number of patients treated per year only
  3. The colour of the treatment room walls
  4. The workload, use factor and occupancy factor for the adjacent area Correct answer.

Explanation

Shielding calculations combine the workload of the accelerator, the use factor for the direction of the beam and the occupancy factor of the adjacent area to estimate the dose at the boundary. These factors determine the required attenuation. Patient numbers alone, wall colour and couch brand do not affect the calculation.

Question 50Radiation Protection and Safety

Which statement about the use of a dose area product (DAP) meter in a radiotherapy planning CT or fluoroscopy suite is correct?

  1. It measures the temperature of the X-ray tube
  2. It provides a measure of the radiation dose to the patient and supports optimisation of the procedure Correct answer.
  3. It measures the dose to the radiographer's hands
  4. It replaces the need for personal dosimetry

Explanation

A dose area product meter measures the product of dose and area, giving an indication of the total radiation delivered to the patient during a procedure. This supports optimisation and comparison with diagnostic reference levels. It does not measure staff hand dose, replace personal dosimetry or measure tube temperature.