Radiographers Registration Assessment - Therapeutic Radiography (Hong Kong)

In megavoltage photon beams, which interaction is the dominant contributor to dose deposition in soft tissue?

• APhotoelectric effect
• BCompton scattering
• CPair production
• DCoherent scattering

What is the primary function of the bending magnet in a medical linear accelerator?

• ATo focus the electron beam to a smaller focal spot size
• BTo deflect the electron beam through a specific angle (e.g., 270 or 90 degrees) to hit th…
• CTo accelerate the electrons to megavoltage energies within the waveguide
• DTo monitor the dose rate, flatness, and symmetry of the beam

For a 6 MV photon beam, at what depth (d_max) does the maximum dose deposition typically occur in water?

• A0.5 cm
• B1.5 cm
• C2.5 cm
• D3.0 cm

In electron beam therapy, what is the approximate relationship between the energy (E in MeV) of the electron beam and its practical range (Rp in cm) in water?

• ARp ≈ E / 4
• BRp ≈ E / 2
• CRp ≈ E * 2
• DRp ≈ E / 3

Which of the following is true regarding the TG-51 calibration protocol for clinical reference dosimetry?

• AIt utilizes an air-kerma calibration factor (Nk)
• BIt requires the use of a water calorimeter as the active detector
• CIt specifies reference dosimetry based on absorbed-dose-to-water calibration factor (Nd,w)
• DIt is only applicable to Cobalt-60 beams

What is the primary function of a flattening filter in a megavoltage linear accelerator?

• ATo produce a uniform dose distribution across the field at a reference depth
• BTo remove low-energy photons from the beam to decrease skin dose
• CTo convert the electron beam into bremsstrahlung X-ray photons
• DTo collimate the beam into a rectangular or square shape

Which radioactive isotope is most commonly used as the source in high-dose-rate (HDR) brachytherapy remote afterloaders?

• ACesium-137
• BIridium-192
• CIodine-125
• DPalladium-103

How does the percentage depth dose (PDD) of a megavoltage photon beam change with an increase in Source-to-Surface Distance (SSD)?

• APDD decreases as SSD increases
• BPDD increases as SSD increases
• CPDD remains constant regardless of SSD changes
• DPDD first increases then decreases due to air scatter

Which of the following describes the 'skin-sparing effect' in megavoltage photon beams?

• ALow absorption of high-energy photons by the epidermis
• BThe electronic build-up region where dose increases from a low surface value to a maximum…
• CGeometric shielding of the skin surface by the primary collimator jaws
• DReduced backscattering of secondary electrons from the air-skin interface

In a linear accelerator, what device is used to generate or amplify microwave power for accelerating electrons in high-energy (> 10 MeV) machines?

• AMagnetron
• BKlystron
• CThyratron
• DWaveguide

What is the primary purpose of the scattering foil in the electron mode of a linear accelerator?

• ATo convert electrons into high-energy X-rays via bremsstrahlung
• BTo spread the narrow, pencil-like electron beam to create a uniform dose distribution
• CTo filter out low-energy photons contaminating the electron beam
• DTo decrease the electron energy to a clinically useful level

What is the physical half-life of the radioactive isotope Cobalt-60?

• A73.8 days
• B5.26 years
• C30 years
• D17 days

What does the Tissue-Maximum Ratio (TMR) represent in photon dose calculations?

• AThe ratio of dose at a given depth to the dose at d_max at a fixed SSD
• BThe ratio of dose at a given depth to the dose at d_max at a fixed Source-to-Axis Distanc…
• CThe ratio of dose in phantom to the dose in free space (air)
• DThe ratio of scattered dose to the primary dose at a given depth

What is the primary physical interaction that leads to high contrast between bone and soft tissue in low-energy diagnostic kilovoltage (kV) imaging compared to megavoltage (MV) therapeutic imaging?

• ACompton scattering
• BPhotoelectric effect
• CPair production
• DRayleigh scattering

Which of the following is an advantage of FFF (Flattening Filter Free) photon beams in modern radiotherapy?

• AEnhanced skin-sparing effect at all depths
• BHigher dose rate leading to shorter treatment times (especially in SRS and SBRT)
• CIncreased peripheral dose outside the treatment field
• DA more uniform flat dose profile across the field at all depths

For a clinical electron beam, what is the meaning of the parameter R50?

• AThe depth at which the absorbed dose falls to 50% of the maximum dose
• BThe range of electrons in centimeters where 50% of electrons have stopped in air
• CThe radius of the applicator cone that yields a 50% field size at the surface
• DThe depth of the 90% dose line relative to the 50% dose line

Which dosimetry detector is most suitable for measuring high-resolution dose distributions in areas with steep dose gradients, such as the penumbra region of a stereotactic collimator?

• AStandard Thimble Ionization Chamber
• BSilicon Diode detector
• CThermoluminescent Dosimeter (TLD) chips
• DParallel-plate ionization chamber

What is the main reason for using a build-up cap over an ionization chamber when measuring dose in a megavoltage photon beam in air?

• ATo protect the chamber wall from mechanical damage and moisture
• BTo establish electronic equilibrium by providing a thickness equal to or greater than the…
• CTo filter out low-energy scatter photons originating from the collimator jaws
• DTo prevent air recombination effects inside the active volume

In brachytherapy, which parameter describes the dose rate at a distance of 1 cm along the transverse axis of a source, relative to the air-kerma strength?

• AAnisotropy function
• BDose rate constant (Lambda)
• CGeometry factor
• DRadial dose function

What is the primary source of photon beam contamination in a clinical electron beam?

• AScatter from the patient's skin surface
• BBremsstrahlung radiation generated in the collimator jaws, scattering foil, and air
• CElectrons backscattered from the floor and walls of the treatment room
• DNeutrons generated by photodisintegration in the treatment head

According to the linear-quadratic (LQ) model of cell survival, what does the alpha/beta ratio represent?

• AThe dose at which the linear and quadratic components of cell kill are equal
• BThe ratio of early-to-late tissue response to fractionated radiation
• CThe slope of the cell survival curve at very low radiation doses
• DThe repair capacity of sublethal damage in tumor cells compared to normal cells

Which of the following tissues or tumors typically exhibits a low alpha/beta ratio (e.g., 1.5 to 3 Gy)?

• ASquamous cell carcinoma of the head and neck
• BEarly-responding normal tissues (e.g., skin, jejunum)
• CLate-responding normal tissues (e.g., spinal cord, kidneys)
• DMost rapidly proliferating lung cancers

What are the '5 Rs' of radiobiology that describe the biological basis of fractionated radiation therapy?

• ARepair, Reoxygenation, Redistribution, Repopulation, Radiosensitivity
• BRegistration, Re-evaluation, Reduction, Reconstruction, Recovery
• CResection, Response, Regeneration, Re-irradiation, Rest
• DRe-alignment, Recalibration, Registration, Resolution, Redosing

Under the Radiation Ordinance (Cap. 303) of Hong Kong, what is the annual effective dose limit for occupational exposure of registered radiation workers?

• A1 mSv
• B20 mSv
• C50 mSv
• D150 mSv

What is the annual equivalent dose limit for the lens of the eye for occupational radiation workers, as updated in recent international recommendations adopted in Hong Kong?

• A150 mSv
• B20 mSv
• C50 mSv
• D500 mSv

In radiation protection, what is the definition of a 'Controlled Area' in a radiotherapy department?

• AAn area where the annual effective dose to any individual is guaranteed to be less than 1…
• BAn area where specific protection measures and safety rules are required to control occup…
• CThe console area where the therapeutic radiographers control the treatment delivery
• DA public waiting area adjacent to the linac console room

Which type of personal radiation monitoring dosimeter utilizes lithium fluoride (LiF) crystals that release light when heated after exposure?

• AOptically Stimulated Luminescence (OSL) dosimeter
• BThermoluminescent Dosimeter (TLD)
• CFilm badge dosimeter
• DGeiger-Müller pocket dosimeter

In the design of a megavoltage radiotherapy room, what is the 'secondary barrier' designed to shield against?

• AThe direct, collimated useful primary beam from the accelerator target
• BLeakage radiation from the treatment head and scattered radiation from the patient and wa…
• CSecondary neutrons generated by photodisintegration only
• DAlpha and beta particles emitted during machine operation

During which phases of the cell cycle are cells typically most sensitive to ionizing radiation?

• ALate S phase
• BG2 and M phases
• CEarly S phase
• DG0 phase

What is the Oxygen Enhancement Ratio (OER) in radiobiology?

• AThe ratio of oxygen concentration in tumor tissue to that in normal tissue
• BThe ratio of the radiation dose required to cause a biological effect in hypoxic conditio…
• CThe rate of oxygen consumption by normal cells during active irradiation
• DThe percentage of hypoxic cells that undergo reoxygenation between fractions

Which of the following is considered a deterministic (tissue reaction) effect of ionizing radiation?

• ARadiation-induced leukemia
• BRadiation-induced thyroid cancer
• CCataract formation in the lens of the eye
• DHereditary genetic mutations in offspring

In linear accelerator room design, what is the primary purpose of incorporating a maze entrance instead of a direct door?

• ATo prevent patients from accidentally leaving the room during treatment
• BTo reduce the radiation dose at the entry door by forcing photons to scatter multiple tim…
• CTo optimize room ventilation and air cooling systems
• DTo provide space for storing thermoplastic masks and positioning cushions

For high-energy photon beams (typically > 10 MV), what type of secondary radiation contamination becomes a major concern for shielding and room activation?

• AAlpha particles
• BNeutrons
• CBeta particles
• DPositrons

According to the ALARA principle, what are the three cardinal principles of radiation protection?

• ATime, Distance, Shielding
• BJustification, Optimization, Limitation
• CCollimation, Filtration, Calibration
• DMonitoring, Recording, Reporting

Under the Code of Practice for radiation protection in Hong Kong, who holds the primary clinical responsibility for the justification of a patient's medical exposure?

• AThe therapeutic radiographer delivering the treatment
• BThe medical physicist verifying the dosimetry
• CThe clinical oncologist prescribing the radiotherapy
• DThe radiation protection officer of the hospital

What is the primary biological mechanism of cell damage by low-LET radiations, such as megavoltage X-rays?

• ADirect ionization of the sugar-phosphate backbone of DNA
• BIndirect action via radiolysis of water molecules, producing free radicals that damage DNA
• CThermal coagulation of nuclear proteins and cytoplasm
• DDisruption of cell membrane transport channels

If a therapeutic radiographer suspects a major patient collision or a serious mechanical malfunction during beam-on, what is the immediate first action?

• ACall the medical physicist on duty immediately
• BPress the emergency stop button on the treatment console or treatment room wall
• CComplete the current treatment fraction and then check the machine log
• DLog out of the treatment software to force a system reboot

What is the annual effective dose limit for members of the general public under the Hong Kong Radiation Ordinance?

• A1 mSv
• B5 mSv
• C15 mSv
• D20 mSv

In structural shielding calculations, what does the occupancy factor (T) represent?

• AThe fraction of the operating day that the treatment beam is directed at the barrier
• BThe fraction of time that the area being shielded is occupied by individuals while the be…
• CThe ratio of staff members to patients in the department
• DThe average number of hours per day the treatment console is active

Which of the following normal organs is considered a serial structure with a low tolerance dose (e.g., TD 5/5 of 45-50 Gy), where exceeding this limit can lead to radiation-induced myelitis?

• ALiver
• BKidney
• CSpinal cord
• DHeart

According to ICRU Report 50 and 62 guidelines, how is the Clinical Target Volume (CTV) defined?

• AThe gross palpable, visible, or clinically demonstrable extent of the malignant growth
• BThe volume containing the gross tumor volume plus a margin for subclinical microscopic ma…
• CThe volume defined by the clinician that must receive a specified dose to achieve treatme…
• DThe volume that accounts for setup uncertainties and internal organ motion during treatme…

What is the primary clinical purpose of administering intravenous contrast media during a CT simulation scan?

• ATo improve the accuracy of the CT number calibration curve
• BTo enhance the visualization of blood vessels and organs to facilitate target and OAR del…
• CTo decrease the required CT scan time and slice thickness
• DTo reduce the radiation dose received by the patient from the CT scanner

In treatment planning, what does a Dose-Volume Histogram (DVH) represent?

• AA spatial map of the dose distribution across a single axial CT slice
• BA 3D surface rendering of the target volume showing hot and cold spots
• CA graphical representation showing the volume of a structure receiving at least a specifi…
• DThe change in dose rate as a function of treatment delivery time

What is the key difference between 'forward planning' and 'inverse planning' in radiotherapy?

• AForward planning is only applicable to electron beams, while inverse planning is used for…
• BInverse planning is used for 3D-CRT, whereas forward planning is used for IMRT and VMAT
• CIn forward planning, the planner manually sets beam parameters and modifies weights; in i…
• DForward planning calculates dose from the inside out, whereas inverse planning calculates…

What CT simulator component is crucial to ensure that the patient setup geometry in the simulator matches the geometry of the treatment room?

• AAn external laser marking system aligned with the CT coordinate system
• BA dual-energy CT detector array
• CAn automatic contrast injector synchronized with the scan start
• DA high-frequency X-ray generator

What is the primary physical significance of the 'Hounsfield Unit' (HU) in a planning CT scan?

• AIt indicates the absolute temperature of the tissue during imaging
• BIt represents the relative electron density of tissues, which is used to calculate tissue…
• CIt defines the physical origin (0,0,0) of the scanner coordinate system
• DIt indicates the spatial resolution and pixel size of the reconstructed image

In ICRU Report 83 recommendations for prescribing and reporting IMRT, what parameter is recommended to represent the near-maximum dose received by the PTV?

• AD98%
• BD50%
• CD2%
• DDmean