FRCR Oncology Part 1: PHYSICS - 2 (2 SETS, 100+100 QUESTIONS, ANSWERS BELOW)

 

Radiation Physics (20 Questions)

1. What is the primary source of bremsstrahlung radiation in a linear accelerator?
   A. Electron collisions with the target nucleus
   B. Photon interactions with the collimator
   C. Neutron capture in the shielding
   D. Electron-positron annihilation
   E. Compton scattering in the patient

2. Which particle is most likely to undergo pair production when interacting with matter?
   A. Electron
   B. Neutron
   C. Proton
   D. Photon
   E. Alpha particle

3. What is the dominant interaction process for 6 MV photons in soft tissue?
   A. Photoelectric effect
   B. Compton scattering
   C. Pair production
   D. Coherent scattering
   E. Photodisintegration

4. What is the approximate half-value layer (HVL) for a 6 MV photon beam in lead?
   A. 0.5 mm
   B. 5 mm
   C. 12 mm
   D. 25 mm
   E. 50 mm

5. Which factor most significantly influences the linear energy transfer (LET) of a charged particle?
   A. Particle mass
   B. Particle charge
   C. Particle velocity
   D. Medium density
   E. Incident energy

6. What is the primary mode of energy loss for a 10 MeV electron in water?
   A. Bremsstrahlung radiation
   B. Collisional interactions
   C. Photoelectric effect
   D. Pair production
   E. Compton scattering

7. Which type of radiation has the highest relative biological effectiveness (RBE)?
   A. Gamma rays
   B. X-rays
   C. Protons
   D. Alpha particles
   E. Electrons

8. What is the energy of a photon emitted when an electron transitions from n=2 to n=1 in a hydrogen atom?
   A. 1.5 eV
   B. 3.4 eV
   C. 10.2 eV
   D. 13.6 eV
   E. 15.8 eV

9. Which process results in the emission of characteristic X-rays?
   A. Electron capture
   B. Inner shell electron ejection
   C. Bremsstrahlung radiation
   D. Compton scattering
   E. Pair production

10. What is the primary interaction mechanism for thermal neutrons in tissue?
    A. Elastic scattering
    B. Inelastic scattering
    C. Neutron capture
    D. Pair production
    E. Compton scattering

11. What is the approximate mass attenuation coefficient for 100 keV photons in bone?
    A. 0.01 cm²/g
    B. 0.1 cm²/g
    C. 0.5 cm²/g
    D. 1.0 cm²/g
    E. 5.0 cm²/g

12. Which factor most significantly affects the range of a proton in tissue?
    A. Proton mass
    B. Initial energy
    C. Tissue density
    D. Atomic number
    E. Beam divergence

13. What is the primary source of neutrons in a high-energy linear accelerator (>10 MV)?
    A. Photon interactions with the target
    B. Electron collisions with the collimator
    C. Photonuclear reactions
    D. Bremsstrahlung radiation
    E. Compton scattering

14. Which equation describes the exponential attenuation of a monoenergetic photon beam?
    A. I = I₀ e^(μx)
    B. I = I₀ e^(-μx)
    C. I = I₀ (1 - μx)
    D. I = I₀ / (1 + μx)
    E. I = I₀ μx

15. What is the dominant interaction for 50 keV photons in soft tissue?
    A. Photoelectric effect
    B. Compton scattering
    C. Pair production
    D. Coherent scattering
    E. Photodisintegration

16. What is the approximate range of a 5 MeV electron in water?
    A. 0.5 cm
    B. 1.5 cm
    C. 2.5 cm
    D. 5.0 cm
    E. 10.0 cm

17. Which property of a material most affects its ability to shield gamma rays?
    A. Density
    B. Atomic number
    C. Thickness
    D. Electron density
    E. Thermal conductivity

18. What is the primary mode of energy deposition for protons in tissue?
    A. Bremsstrahlung radiation
    B. Collisional interactions
    C. Compton scattering
    D. Pair production
    E. Photoelectric effect

19. Which type of radiation is least penetrating in tissue?
    A. Gamma rays
    B. X-rays
    C. Beta particles
    D. Alpha particles
    E. Neutrons

20. What is the approximate energy threshold for pair production in tissue?
    A. 0.511 MeV
    B. 1.022 MeV
    C. 2.044 MeV
    D. 5.110 MeV
    E. 10.220 MeV

Dosimetry (20 Questions)

21. What is the SI unit of absorbed dose?
    A. Sievert
    B. Gray
    C. Becquerel
    D. Coulomb/kg
    E. Roentgen

22. Which quantity represents the radiation dose equivalent?
    A. Absorbed dose
    B. Equivalent dose
    C. Effective dose
    D. Kerma
    E. Exposure

23. What is the quality factor for alpha particles in radiation protection?
    A. 1
    B. 5
    C. 10
    D. 20
    E. 50

24. What is the approximate dose rate at 2 meters from a 1 GBq point source of Co-60 (ignoring shielding)?
    A. 0.01 mGy/h
    B. 0.1 mGy/h
    C. 1 mGy/h
    D. 10 mGy/h
    E. 100 mGy/h

25. Which dosimeter is most suitable for real-time dose monitoring in radiotherapy?
    A. Film badge
    B. Thermoluminescent dosimeter (TLD)
    C. Ionisation chamber
    D. Optically stimulated luminescence (OSL) dosimeter
    E. Pocket dosimeter

26. What is the primary purpose of the percentage depth dose (PDD) in radiotherapy?
    A. To measure surface dose
    B. To quantify dose distribution with depth
    C. To calculate monitor units
    D. To assess beam flatness
    E. To determine penumbra width

27. What is the approximate Dmax for a 6 MV photon beam in water?
    A. 0.5 cm
    B. 1.5 cm
    C. 2.5 cm
    D. 3.5 cm
    E. 5.0 cm

28. Which factor most significantly affects the output factor of a linear accelerator?
    A. Beam energy
    B. Field size
    C. Source-to-surface distance
    D. Collimator angle
    E. Gantry angle

29. What is the primary advantage of using a Farmer-type ionisation chamber in radiotherapy dosimetry?
    A. High spatial resolution
    B. Energy independence
    C. Small size
    D. Real-time readout
    E. Low cost

30. What is the tissue-air ratio (TAR) used for in radiotherapy planning?
    A. To calculate scatter dose
    B. To quantify dose at depth for fixed SSD
    C. To measure beam penumbra
    D. To assess beam flatness
    E. To determine monitor units

31. Which quantity is most relevant for assessing stochastic radiation risks?
    A. Absorbed dose
    B. Equivalent dose
    C. Effective dose
    D. Kerma
    E. Exposure

32. What is the approximate absorbed dose from a 1 mSv effective dose of gamma rays to soft tissue?
    A. 0.1 mGy
    B. 1 mGy
    C. 10 mGy
    D. 100 mGy
    E. 1000 mGy

33. Which calibration protocol is most commonly used for radiotherapy beam dosimetry in the UK?
    A. TG-21
    B. TG-51
    C. IAEA TRS-398
    D. AAPM TG-61
    E. IPEM Code of Practice

34. What is the primary source of uncertainty in thermoluminescent dosimetry?
    A. Energy dependence
    B. Spatial resolution
    C. Readout time
    D. Calibration stability
    E. Detector size

35. What is the monitor unit (MU) calculation factor for inverse square law correction?
    A. (SSD + dmax)² / (SAD)²
    B. (SAD)² / (SSD + dmax)²
    C. (SSD)² / (SAD)²
    D. (SAD)² / (SSD)²
    E. (SSD + dmax)² / (SSD)²

36. Which dosimeter is most suitable for in-vivo dosimetry during radiotherapy?
    A. Film badge
    B. TLD
    C. MOSFET
    D. OSL dosimeter
    E. Geiger-Müller counter

37. What is the primary purpose of the backscatter factor (BSF) in radiotherapy?
    A. To quantify scatter dose at the surface
    B. To measure dose at depth
    C. To calculate monitor units
    D. To assess beam flatness
    E. To determine penumbra width

38. What is the approximate penumbra width for a 6 MV photon beam at 10 cm depth?
    A. 1 mm
    B. 3 mm
    C. 5 mm
    D. 10 mm
    E. 15 mm

39. Which factor most significantly affects the dose rate from a brachytherapy source?
    A. Source activity
    B. Source energy
    C. Source size
    D. Source material
    E. Source shape

40. What is the primary advantage of gel dosimetry in radiotherapy?
    A. Low cost
    B. Real-time readout
    C. 3D dose distribution measurement
    D. Energy independence
    E. Small size

Radiotherapy Treatment Planning (20 Questions)

41. What is the primary purpose of a multileaf collimator (MLC) in radiotherapy?
    A. To filter low-energy photons
    B. To shape the radiation field
    C. To increase beam energy
    D. To reduce scatter radiation
    E. To monitor dose delivery

42. Which parameter is most critical for defining the planning target volume (PTV)?
    A. Tumour size
    B. Organ motion
    C. Beam energy
    D. Field size
    E. Monitor units

43. What is the primary advantage of intensity-modulated radiotherapy (IMRT) over 3D conformal radiotherapy?
    A. Reduced treatment time
    B. Improved dose conformity
    C. Lower cost
    D. Increased scatter dose
    E. Simplified planning

44. Which algorithm is most accurate for dose calculation in heterogeneous tissues?
    A. Pencil beam
    B. Convolution-superposition
    C. Monte Carlo
    D. Clarkson integration
    E. Batho correction

45. What is the primary purpose of a bolus in radiotherapy?
    A. To increase beam energy
    B. To reduce skin sparing
    C. To shape the radiation field
    D. To monitor dose delivery
    E. To reduce scatter radiation

46. Which factor most significantly affects the dose distribution in proton therapy?
    A. Beam energy
    B. Field size
    C. Gantry angle
    D. Collimator shape
    E. Monitor units

47. What is the primary advantage of stereotactic body radiotherapy (SBRT)?
    A. Reduced total dose
    B. High dose per fraction
    C. Increased treatment time
    D. Lower cost
    E. Simplified planning

48. Which parameter is most critical for image-guided radiotherapy (IGRT)?
    A. Beam energy
    B. Image registration accuracy
    C. Field size
    D. Monitor units
    E. Collimator angle

49. What is the primary purpose of a wedge filter in radiotherapy?
    A. To increase beam energy
    B. To compensate for tissue heterogeneity
    C. To shape the radiation field
    D. To reduce scatter radiation
    E. To monitor dose delivery

50. Which factor most significantly affects the dose fall-off in proton therapy?
    A. Bragg peak position
    B. Field size
    C. Gantry angle
    D. Collimator shape
    E. Monitor units

51. What is the primary advantage of volumetric modulated arc therapy (VMAT)?
    A. Reduced treatment time
    B. Increased scatter dose
    C. Simplified planning
    D. Lower cost
    E. Reduced dose conformity

52. Which structure is most critical for dose constraints in head and neck radiotherapy?
    A. Spinal cord
    B. Liver
    C. Kidneys
    D. Lungs
    E. Bladder

53. What is the primary purpose of a compensator in radiotherapy?
    A. To increase beam energy
    B. To correct for tissue inhomogeneity
    C. To shape the radiation field
    D. To reduce scatter radiation
    E. To monitor dose delivery

54. Which factor most significantly affects the penumbra in IMRT?
    A. MLC leaf width
    B. Beam energy
    C. Field size
    D. Gantry angle
    E. Monitor units

55. What is the primary advantage of adaptive radiotherapy?
    A. Reduced treatment time
    B. Adjustment for anatomical changes
    C. Lower cost
    D. Increased scatter dose
    E. Simplified planning

56. Which parameter is most critical for defining the clinical target volume (CTV)?
    A. Tumour size
    B. Microscopic disease extent
    C. Organ motion
    D. Beam energy
    E. Field size

57. What is the primary purpose of a beam spoiler in electron therapy?
    A. To increase beam energy
    B. To reduce skin sparing
    C. To shape the radiation field
    D. To monitor dose delivery
    E. To reduce scatter radiation

58. Which factor most significantly affects the dose distribution in brachytherapy?
    A. Source position
    B. Beam energy
    C. Field size
    D. Gantry angle
    E. Monitor units

59. What is the primary advantage of MR-guided radiotherapy?
    A. Reduced treatment time
    B. Superior soft tissue contrast
    C. Lower cost
    D. Increased scatter dose
    E. Simplified planning

60. Which parameter is most critical for dose-volume histogram (DVH) analysis?
    A. Beam energy
    B. Volume of organ at risk
    C. Field size
    D. Monitor units
    E. Collimator angle

Imaging (20 Questions)

61. What is the primary advantage of CT imaging in radiotherapy planning?
    A. High soft tissue contrast
    B. Low radiation dose
    C. Electron density information
    D. Real-time imaging
    E. Low cost

62. Which imaging modality is most suitable for assessing tumour motion in lung radiotherapy?
    A. CT
    B. MRI
    C. PET
    D. 4D-CT
    E. Ultrasound

63. What is the primary source of contrast in T2-weighted MRI?
    A. Proton density
    B. Tissue relaxation time
    C. Electron density
    D. Atomic number
    E. Blood flow

64. Which factor most significantly affects the spatial resolution in CT imaging?
    A. Slice thickness
    B. Tube current
    C. Tube voltage
    D. Reconstruction algorithm
    E. Field of view

65. What is the primary advantage of PET imaging in oncology?
    A. High spatial resolution
    B. Low radiation dose
    C. Metabolic information
    D. Real-time imaging
    E. Low cost

66. Which radionuclide is most commonly used in PET imaging for oncology?
    A. Tc-99m
    B. I-131
    C. F-18
    D. Co-60
    E. Cs-137

67. What is the primary purpose of a Hounsfield unit in CT imaging?
    A. To measure radiation dose
    B. To quantify tissue density
    C. To assess image contrast
    D. To determine spatial resolution
    E. To monitor image noise

68. Which factor most significantly affects the signal-to-noise ratio in MRI?
    A. Field strength
    B. Slice thickness
    C. Tube current
    D. Reconstruction algorithm
    E. Field of view

69. What is the primary advantage of cone-beam CT (CBCT) in radiotherapy?
    A. High soft tissue contrast
    B. Low radiation dose
    C. On-board imaging for setup verification
    D. Real-time imaging
    E. Low cost

70. Which imaging modality is most suitable for delineating brain tumours in radiotherapy planning?
    A. CT
    B. MRI
    C. PET
    D. 4D-CT
    E. Ultrasound

71. What is the primary source of image noise in CT imaging?
    A. Photon scattering
    B. Detector efficiency
    C. Tube voltage
    D. Reconstruction algorithm
    E. Patient motion

72. Which factor most significantly affects the contrast resolution in MRI?
    A. Field strength
    B. Slice thickness
    C. Tube current
    D. Reconstruction algorithm
    E. Field of view

73. What is the primary advantage of functional MRI in radiotherapy planning?
    A. High spatial resolution
    B. Low radiation dose
    C. Assessment of tumour physiology
    D. Real-time imaging
    E. Low cost

74. Which imaging modality is most suitable for assessing bone metastases in radiotherapy planning?
    A. CT
    B. MRI
    C. PET
    D. 4D-CT
    E. Ultrasound

75. What is the primary purpose of image registration in radiotherapy?
    A. To measure radiation dose
    B. To align multiple imaging datasets
    C. To assess image contrast
    D. To determine spatial resolution
    E. To monitor image noise

76. Which factor most significantly affects the temporal resolution in 4D-CT imaging?
    A. Gantry rotation speed
    B. Tube current
    C. Tube voltage
    D. Reconstruction algorithm
    E. Field of view

77. What is the primary advantage of diffusion-weighted MRI in oncology?
    A. High spatial resolution
    B. Low radiation dose
    C. Assessment of cellularity
    D. Real-time imaging
    E. Low cost

78. Which imaging modality is most suitable for real-time tumour tracking during radiotherapy?
    A. CT
    B. MRI
    C. PET
    D. Fluoroscopy
    E. Ultrasound

79. What is the primary source of contrast in PET imaging?
    A. Proton density
    B. Tissue relaxation time
    C. Electron density
    D. Radiotracer uptake
    E. Blood flow

80. Which factor most significantly affects the radiation dose in CT imaging?
    A. Slice thickness
    B. Tube current
    C. Reconstruction algorithm
    D. Field of view
    E. Patient size

Radiation Protection (20 Questions)

81. What is the annual effective dose limit for radiation workers in the UK?
    A. 1 mSv
    B. 5 mSv
    C. 20 mSv
    D. 50 mSv
    E. 100 mSv

82. Which material is most effective for shielding neutrons?
    A. Lead
    B. Concrete
    C. Water
    D. Boron
    E. Steel

83. What is the primary purpose of the ALARA principle in radiation protection?
    A. To maximize radiation dose
    B. To minimize radiation exposure
    C. To measure radiation dose
    D. To calibrate dosimeters
    E. To monitor radiation levels

84. Which factor most significantly affects the occupational dose in radiotherapy?
    A. Beam energy
    B. Shielding design
    C. Field size
    D. Gantry angle
    E. Monitor units

85. What is the approximate tenth-value layer (TVL) for a 6 MV photon beam in concrete?
    A. 5 cm
    B. 15 cm
    C. 30 cm
    D. 50 cm
    E. 100 cm

86. Which type of personal dosimeter is most suitable for monitoring occupational exposure?
    A. Film badge
    B. TLD
    C. MOSFET
    D. OSL dosimeter
    E. Geiger-Müller counter

87. What is the primary source of stray radiation in a radiotherapy treatment room?
    A. Primary beam
    B. Scatter from patient
    C. Leakage from linac head
    D. Bremsstrahlung radiation
    E. Compton scattering

88. Which regulation governs radiation protection in the UK?
    A. IR(ME)R 2017
    B. IRR 2017
    C. RIDDOR 2013
    D. COSHH 2002
    E. MHRA 2008

89. What is the approximate dose rate reduction factor at 2 meters compared to 1 meter from a point source?
    A. 1/2
    B. 1/4
    C. 1/8
    D. 1/16
    E. 1/32

90. Which factor most significantly affects the design of a radiotherapy bunker?
    A. Beam energy
    B. Field size
    C. Gantry angle
    D. Monitor units
    E. Patient size

91. What is the primary purpose of a controlled area in a radiotherapy department?
    A. To store radioactive sources
    B. To restrict access to radiation hazards
    C. To monitor patient doses
    D. To calibrate dosimeters
    E. To perform quality assurance

92. Which material is most effective for shielding gamma rays?
    A. Lead
    B. Concrete
    C. Water
    D. Boron
    E. Steel

93. What is the annual effective dose limit for the public in the UK?
    A. 1 mSv
    B. 5 mSv
    C. 20 mSv
    D. 50 mSv
    E. 100 mSv

94. Which factor most significantly affects the dose to a fetus in a pregnant patient undergoing radiotherapy?
    A. Beam energy
    B. Shielding placement
    C. Field size
    D. Gantry angle
    E. Monitor units

95. What is the primary advantage of a maze design in a radiotherapy bunker?
    A. Reduced construction cost
    B. Minimized neutron scatter
    C. Increased patient comfort
    D. Simplified quality assurance
    E. Enhanced beam delivery

96. Which type of radiation is most hazardous in terms of external exposure?
    A. Alpha particles
    B. Beta particles
    C. Gamma rays
    D. Neutrons
    E. X-rays

97. What is the primary purpose of a radiation protection advisor (RPA) in radiotherapy?
    A. To deliver radiotherapy
    B. To ensure compliance with regulations
    C. To calibrate dosimeters
    D. To monitor patient doses
    E. To perform quality assurance

98. Which factor most significantly affects the dose rate from a sealed radioactive source?
    A. Source activity
    B. Source energy
    C. Source size
    D. Source material
    E. Source shape

99. What is the approximate half-life of Co-60 used in radiotherapy?
    A. 1.2 years
    B. 2.7 years
    C. 5.3 years
    D. 8.0 years
    E. 12.3 years

100. Which principle is most critical for reducing patient dose in diagnostic imaging?
     A. Time
     B. Distance
     C. Shielding
     D. Justification
     E. Calibration

Answers

Radiation Physics

1. A. Bremsstrahlung radiation arises from electron collisions with the target nucleus in a linac.

2. D. Pair production requires photons with energy >1.022 MeV interacting with a nucleus.

3. B. Compton scattering dominates for 6 MV photons in soft tissue due to energy and Z.

4. C. The HVL for 6 MV photons in lead is approximately 12 mm.

5. B. Particle charge most significantly affects LET, as LET ∝ Z²/v².

6. B. Collisional interactions (ionization) dominate for 10 MeV electrons in water.

7. D. Alpha particles have the highest RBE due to high LET.

8. C. E = 13.6 eV × (1/1² - 1/2²) = 10.2 eV for n=2 to n=1 transition.

9. B. Characteristic X-rays are emitted after inner shell electron ejection.

10. C. Neutron capture (e.g., H-1 to H-2) is the primary interaction for thermal neutrons.

11. C. The mass attenuation coefficient for 100 keV photons in bone is ~0.5 cm²/g.

12. B. Initial energy determines the range of protons in tissue (R ∝ E¹·⁵).

13. C. Photonuclear reactions produce neutrons in high-energy linacs (>10 MV).

14. B. I = I₀ e^(-μx) describes exponential attenuation of photons.

15. A. Photoelectric effect dominates for 50 keV photons in soft tissue (Z³/E³).

16. C. The range of a 5 MeV electron in water is ~2.5 cm (R ≈ 0.5 E).

17. A. Density is the primary factor for gamma ray shielding (μ ∝ ρ).

18. B. Protons deposit energy primarily via collisional interactions.

19. D. Alpha particles are least penetrating due to high LET and charge.

20. B. Pair production requires a minimum photon energy of 1.022 MeV (2m₀c²).

Dosimetry

21. B. The Gray (Gy) is the SI unit of absorbed dose (J/kg).

22. B. Equivalent dose (Sv) accounts for radiation type via quality factor.

23. D. The quality factor for alpha particles is 20 in radiation protection.

24. B. Dose rate for Co-60 (Γ = 1.32 R·m²/Ci·h) at 2 m ≈ 0.1 mGy/h for 1 GBq.

25. C. Ionisation chambers provide real-time dose monitoring in radiotherapy.

26. B. PDD quantifies dose distribution with depth for a given beam.

27. B. Dmax for a 6 MV photon beam in water is ~1.5 cm.

28. B. Field size affects scatter, significantly altering the output factor.

29. B. Farmer-type chambers have energy independence for radiotherapy beams.

30. B. TAR quantifies dose at depth for fixed SSD in isocentric setups.

31. C. Effective dose (Sv) assesses stochastic risks across organs.

32. B. For gamma rays (Q=1), 1 mSv effective dose ≈ 1 mGy absorbed dose.

33. C. IAEA TRS-398 is the standard calibration protocol in the UK.

34. A. Energy dependence is the primary source of uncertainty in TLDs.

35. B. MU correction uses (SAD)² / (SSD + dmax)² for inverse square law.

36. C. MOSFETs are ideal for in-vivo dosimetry due to small size and real-time readout.

37. A. BSF quantifies scatter dose at the surface relative to free space.

38. D. Penumbra width for 6 MV photons at 10 cm depth is ~10 mm.

39. A. Source activity determines the dose rate in brachytherapy.

40. C. Gel dosimetry enables 3D dose distribution measurement.

Radiotherapy Treatment Planning

41. B. MLCs shape the radiation field to conform to the target.

42. B. Organ motion is critical for PTV margins (PTV = CTV + margin).

43. B. IMRT improves dose conformity to complex target volumes.

44. C. Monte Carlo algorithms are most accurate for heterogeneous tissues.

45. B. Bolus reduces skin sparing by increasing surface dose.

46. A. Beam energy determines the depth of the Bragg peak in proton therapy.

47. B. SBRT uses high dose per fraction for improved tumour control.

48. B. Image registration accuracy is critical for IGRT setup correction.

49. B. Wedge filters compensate for tissue heterogeneity or sloping surfaces.

50. A. The Bragg peak position determines dose fall-off in proton therapy.

51. A. VMAT reduces treatment time via continuous arc delivery.

52. A. The spinal cord is critical for dose constraints in head and neck radiotherapy.

53. B. Compensators correct for tissue inhomogeneity in dose distribution.

54. A. MLC leaf width significantly affects penumbra in IMRT.

55. B. Adaptive radiotherapy adjusts for anatomical changes during treatment.

56. B. Microscopic disease extent defines the CTV.

57. B. Beam spoilers reduce skin sparing in electron therapy.

58. A. Source position determines dose distribution in brachytherapy.

59. B. MR-guided radiotherapy offers superior soft tissue contrast.

60. B. Volume of organ at risk is critical for DVH analysis.

Imaging

61. C. CT provides electron density information for dose calculations.

62. D. 4D-CT assesses tumour motion in lung radiotherapy.

63. B. T2-weighted MRI contrast depends on tissue relaxation time.

64. A. Slice thickness most significantly affects CT spatial resolution.

65. C. PET provides metabolic information for tumour staging.

66. C. F-18 (e.g., FDG) is most commonly used in oncology PET imaging.

67. B. Hounsfield units quantify tissue density in CT imaging.

68. A. Field strength most significantly affects MRI signal-to-noise ratio.

69. C. CBCT enables on-board imaging for setup verification.

70. B. MRI is ideal for delineating brain tumours due to soft tissue contrast.

71. A. Photon scattering is the primary source of CT image noise.

72. A. Field strength most significantly affects MRI contrast resolution.

73. C. Functional MRI assesses tumour physiology (e.g., perfusion).

74. C. PET is ideal for assessing bone metastases due to metabolic sensitivity.

75. B. Image registration aligns multiple imaging datasets for planning.

76. A. Gantry rotation speed affects temporal resolution in 4D-CT.

77. C. Diffusion-weighted MRI assesses cellularity in tumours.

78. D. Fluoroscopy enables real-time tumour tracking during radiotherapy.

79. D. Radiotracer uptake provides contrast in PET imaging.

80. B. Tube current most significantly affects CT radiation dose.

Radiation Protection

81. C. The annual effective dose limit for radiation workers is 20 mSv.

82. D. Boron is most effective for neutron shielding due to high capture cross-section.

83. B. ALARA aims to minimize radiation exposure.

84. B. Shielding design most significantly affects occupational dose.

85. C. The TVL for 6 MV photons in concrete is ~30 cm.

86. D. OSL dosimeters are suitable for monitoring occupational exposure.

87. C. Leakage from the linac head is the primary stray radiation source.

88. B. IRR 2017 governs radiation protection in the UK.

89. B. Dose rate reduces by 1/4 at 2 m vs. 1 m (inverse square law).

90. A. Beam energy determines bunker shielding requirements.

91. B. Controlled areas restrict access to radiation hazards.

92. A. Lead is most effective for gamma ray shielding (high Z).

93. A. The annual effective dose limit for the public is 1 mSv.

94. B. Shielding placement most significantly affects fetal dose.

95. B. Maze design minimizes neutron scatter in bunkers.

96. D. Neutrons are most hazardous externally due to high RBE.

97. B. RPAs ensure compliance with radiation protection regulations.

98. A. Source activity determines the dose rate from sealed sources.

99. C. The half-life of Co-60 is ~5.3 years.

100. D. Justification ensures imaging doses are clinically necessary.

Radiation Physics (20 Questions)

101. What is the primary source of characteristic X-rays in a linac target?
     A. Bremsstrahlung radiation
     B. Electron collisions with outer shell electrons
     C. Electron ejection from inner shells
     D. Photon scattering in the target
     E. Neutron capture

102. Which interaction process dominates for 15 MV photons in bone?
     A. Photoelectric effect
     B. Compton scattering
     C. Pair production
     D. Coherent scattering
     E. Photodisintegration

103. What is the approximate half-value layer (HVL) for a 10 MV photon beam in concrete?
     A. 5 cm
     B. 15 cm
     C. 25 cm
     D. 35 cm
     E. 50 cm

104. Which factor most significantly affects the bremsstrahlung yield for electrons?
     A. Electron energy
     B. Target atomic number
     C. Target thickness
     D. Beam divergence
     E. Collimator design

105. What is the primary mode of energy loss for a 200 MeV proton in tissue?
     A. Bremsstrahlung radiation
     B. Collisional interactions
     C. Nuclear interactions
     D. Compton scattering
     E. Pair production

106. Which type of radiation has the lowest quality factor in radiation protection?
     A. Gamma rays
     B. Neutrons
     C. Protons
     D. Alpha particles
     E. Heavy ions

107. What is the approximate energy of a photon emitted during a K-shell transition in tungsten (Z=74)?
     A. 10 keV
     B. 30 keV
     C. 60 keV
     D. 90 keV
     E. 120 keV

108. Which process is most likely to occur for 1 keV photons in soft tissue?
     A. Photoelectric effect
     B. Compton scattering
     C. Pair production
     D. Coherent scattering
     E. Photodisintegration

109. What is the primary interaction mechanism for fast neutrons in tissue?
     A. Elastic scattering
     B. Inelastic scattering
     C. Neutron capture
     D. Pair production
     E. Compton scattering

110. What is the approximate mass energy absorption coefficient for 1 MeV photons in water?
     A. 0.01 cm²/g
     B. 0.03 cm²/g
     C. 0.1 cm²/g
     D. 0.3 cm²/g
     E. 1.0 cm²/g

111. Which factor most significantly affects the range of an alpha particle in tissue?
     A. Particle mass
     B. Initial energy
     C. Tissue density
     D. Atomic number
     E. Beam divergence

112. What is the primary source of scatter radiation in a radiotherapy treatment room?
     A. Primary beam
     B. Patient tissues
     C. Linac head
     D. Collimator
     E. Shielding walls

113. Which equation describes the dose rate from a point source?
     A. D = ΓA / r
     B. D = ΓA / r²
     C. D = ΓA r
     D. D = ΓA r²
     E. D = ΓA e^(-r)

114. What is the dominant interaction for 200 keV photons in bone?
     A. Photoelectric effect
     B. Compton scattering
     C. Pair production
     D. Coherent scattering
     E. Photodisintegration

115. What is the approximate range of a 10 MeV electron in tissue?
     A. 1 cm
     B. 3 cm
     C. 5 cm
     D. 7 cm
     E. 10 cm

116. Which property of a material most affects its ability to shield neutrons?
     A. Density
     B. Atomic number
     C. Hydrogen content
     D. Electron density
     E. Thermal conductivity

117. What is the primary mode of energy deposition for carbon ions in tissue?
     A. Bremsstrahlung radiation
     B. Collisional interactions
     C. Compton scattering
     D. Pair production
     E. Nuclear interactions

118. Which type of radiation is most effectively shielded by low-Z materials?
     A. Gamma rays
     B. X-rays
     C. Beta particles
     D. Neutrons
     E. Alpha particles

119. What is the approximate energy threshold for photodisintegration in tissue?
     A. 1 MeV
     B. 5 MeV
     C. 10 MeV
     D. 20 MeV
     E. 50 MeV

120. What is the primary source of X-rays in a diagnostic X-ray tube?
     A. Bremsstrahlung radiation
     B. Characteristic radiation
     C. Compton scattering
     D. Pair production
     E. Photonuclear reactions

Dosimetry (20 Questions)

121. What is the SI unit of equivalent dose?
     A. Gray
     B. Sievert
     C. Becquerel
     D. Coulomb/kg
     E. Roentgen

122. Which quantity is most relevant for assessing deterministic radiation effects?
     A. Absorbed dose
     B. Equivalent dose
     C. Effective dose
     D. Kerma
     E. Exposure

123. What is the quality factor for fast neutrons in radiation protection?
     A. 1
     B. 5
     C. 10
     D. 20
     E. 50

124. What is the approximate dose rate at 1 meter from a 2 GBq point source of I-131 (ignoring shielding)?
     A. 0.02 mGy/h
     B. 0.2 mGy/h
     C. 2 mGy/h
     D. 20 mGy/h
     E. 200 mGy/h

125. Which dosimeter is most suitable for measuring low-dose environmental radiation?
     A. Film badge
     B. TLD
     C. Ionisation chamber
     D. OSL dosimeter
     E. Geiger-Müller counter

126. What is the primary purpose of the tissue maximum ratio (TMR) in radiotherapy?
     A. To measure surface dose
     B. To quantify dose at depth for isocentric setups
     C. To calculate monitor units
     D. To assess beam flatness
     E. To determine penumbra width

127. What is the approximate Dmax for a 15 MV photon beam in water?
     A. 1.0 cm
     B. 2.0 cm
     C. 3.0 cm
     D. 4.0 cm
     E. 5.0 cm

128. Which factor most significantly affects the scatter factor in radiotherapy?
     A. Beam energy
     B. Field size
     C. Source-to-surface distance
     D. Collimator angle
     E. Gantry angle

129. What is the primary advantage of using a parallel-plate ionisation chamber in electron dosimetry?
     A. High spatial resolution
     B. Energy independence
     C. Small volume for shallow depths
     D. Real-time readout
     E. Low cost

130. What is the primary purpose of the output factor in radiotherapy?
     A. To quantify scatter dose
     B. To measure dose at depth
     C. To normalize dose for field size
     D. To assess beam flatness
     E. To determine penumbra width

131. Which quantity is most relevant for assessing occupational radiation exposure?
     A. Absorbed dose
     B. Equivalent dose
     C. Effective dose
     D. Kerma
     E. Exposure

132. What is the approximate absorbed dose from a 10 mSv effective dose of neutrons (Q=10) to soft tissue?
     A. 0.1 mGy
     B. 1 mGy
     C. 10 mGy
     D. 100 mGy
     E. 1000 mGy

133. Which calibration protocol is most suitable for low-energy X-ray dosimetry?
     A. TG-21
     B. TG-51
     C. IAEA TRS-398
     D. AAPM TG-61
     E. IPEM Code of Practice

134. What is the primary source of uncertainty in MOSFET dosimetry?
     A. Energy dependence
     B. Spatial resolution
     C. Readout time
     D. Calibration stability
     E. Detector size

135. What is the monitor unit (MU) calculation factor for tissue inhomogeneity correction?
     A. TAR
     B. TMR
     C. Effective path length
     D. Output factor
     E. Scatter factor

136. Which dosimeter is most suitable for postal dosimetry audits?
     A. Film badge
     B. TLD
     C. MOSFET
     D. OSL dosimeter
     E. Geiger-Müller counter

137. What is the primary purpose of the collimator scatter factor (Sc)?
     A. To quantify scatter from the patient
     B. To measure dose at depth
     C. To normalize dose for collimator settings
     D. To assess beam flatness
     E. To determine penumbra width

138. What is the approximate penumbra width for a 15 MV photon beam at 10 cm depth?
     A. 2 mm
     B. 5 mm
     C. 8 mm
     D. 12 mm
     E. 18 mm

139. Which factor most significantly affects the dose rate from an HDR brachytherapy source?
     A. Source activity
     B. Source energy
     C. Source size
     D. Source material
     E. Source shape

140. What is the primary advantage of diode detectors in small-field dosimetry?
     A. Low cost
     B. Energy independence
     C. High spatial resolution
     D. Real-time readout
     E. Large volume

Radiotherapy Treatment Planning (20 Questions)

141. What is the primary purpose of dynamic MLC in IMRT?
     A. To filter low-energy photons
     B. To modulate beam intensity
     C. To increase beam energy
     D. To reduce scatter radiation
     E. To monitor dose delivery

142. Which parameter is most critical for defining the gross tumour volume (GTV)?
     A. Tumour motion
     B. Microscopic disease
     C. Visible tumour extent
     D. Beam energy
     E. Field size

143. What is the primary advantage of proton therapy over photon therapy?
     A. Reduced treatment time
     B. Sharp dose fall-off at Bragg peak
     C. Lower cost
     D. Increased scatter dose
     E. Simplified planning

144. Which algorithm is most suitable for dose calculation in lung radiotherapy?
     A. Pencil beam
     B. Convolution-superposition
     C. Monte Carlo
     D. Clarkson integration
     E. Batho correction

145. What is the primary purpose of a tissue compensator in electron therapy?
     A. To increase beam energy
     B. To correct for surface irregularities
     C. To shape the radiation field
     D. To monitor dose delivery
     E. To reduce scatter radiation

146. Which factor most significantly affects the dose distribution in carbon ion therapy?
     A. Beam energy
     B. Field size
     C. Gantry angle
     D. Collimator shape
     E. Monitor units

147. What is the primary advantage of stereotactic radiosurgery (SRS)?
     A. Reduced total dose
     B. High precision for small targets
     C. Increased treatment time
     D. Lower cost
     E. Simplified planning

148. Which parameter is most critical for adaptive radiotherapy?
     A. Beam energy
     B. Anatomical change detection
     C. Field size
     D. Monitor units
     E. Collimator angle

149. What is the primary purpose of a dynamic wedge in radiotherapy?
     A. To increase beam energy
     B. To modulate dose distribution
     C. To shape the radiation field
     D. To reduce scatter radiation
     E. To monitor dose delivery

150. Which factor most significantly affects the dose fall-off in electron therapy?
     A. Beam energy
     B. Field size
     C. Gantry angle
     D. Collimator shape
     E. Monitor units

151. What is the primary advantage of tomotherapy over conventional IMRT?
     A. Reduced treatment time
     B. Integrated image guidance
     C. Lower cost
     D. Increased scatter dose
     E. Simplified planning

152. Which structure is most critical for dose constraints in pelvic radiotherapy?
     A. Spinal cord
     B. Rectum
     C. Kidneys
     D. Lungs
     E. Brain

153. What is the primary purpose of a beam modifier in radiotherapy?
     A. To increase beam energy
     B. To optimize dose distribution
     C. To shape the radiation field
     D. To reduce scatter radiation
     E. To monitor dose delivery

154. Which factor most significantly affects the penumbra in proton therapy?
     A. Beam scattering
     B. Beam energy
     C. Field size
     D. Gantry angle
     E. Monitor units

155. What is the primary advantage of 4D radiotherapy?
     A. Reduced treatment time
     B. Motion management
     C. Lower cost
     D. Increased scatter dose
     E. Simplified planning

156. Which parameter is most critical for defining the internal target volume (ITV)?
     A. Tumour size
     B. Microscopic disease
     C. Tumour motion
     D. Beam energy
     E. Field size

157. What is the primary purpose of a cut-out in electron therapy?
     A. To increase beam energy
     B. To shape the radiation field
     C. To reduce skin sparing
     D. To monitor dose delivery
     E. To reduce scatter radiation

158. Which factor most significantly affects the dose distribution in HDR brachytherapy?
     A. Dwell time
     B. Beam energy
     C. Field size
     D. Gantry angle
     E. Monitor units

159. What is the primary advantage of CT-guided radiotherapy?
     A. Reduced treatment time
     B. Accurate electron density information
     C. Lower cost
     D. Increased scatter dose
     E. Simplified planning

160. Which parameter is most critical for normal tissue complication probability (NTCP) analysis?
     A. Beam energy
     B. Organ-at-risk dose
     C. Field size
     D. Monitor units
     E. Collimator angle

Imaging (20 Questions)

161. What is the primary advantage of MRI in radiotherapy planning?
     A. High spatial resolution
     B. Low radiation dose
     C. Superior soft tissue contrast
     D. Real-time imaging
     E. Low cost

162. Which imaging modality is most suitable for assessing cardiac motion in radiotherapy?
     A. CT
     B. MRI
     C. PET
     D. 4D-CT
     E. Ultrasound

163. What is the primary source of contrast in T1-weighted MRI?
     A. Proton density
     B. Tissue relaxation time
     C. Electron density
     D. Atomic number
     E. Blood flow

164. Which factor most significantly affects the contrast resolution in CT imaging?
     A. Slice thickness
     B. Tube current
     C. Tube voltage
     D. Reconstruction algorithm
     E. Field of view

165. What is the primary advantage of SPECT imaging in oncology?
     A. High spatial resolution
     B. Low radiation dose
     C. Functional information
     D. Real-time imaging
     E. Low cost

166. Which radionuclide is most commonly used in SPECT imaging for oncology?
     A. Tc-99m
     B. I-131
     C. F-18
     D. Co-60
     E. Cs-137

167. What is the primary purpose of a window level in CT imaging?
     A. To measure radiation dose
     B. To adjust image contrast
     C. To assess image noise
     D. To determine spatial resolution
     E. To monitor patient motion

168. Which factor most significantly affects the spatial resolution in MRI?
     A. Field strength
     B. Gradient strength
     C. Tube current
     D. Reconstruction algorithm
     E. Field of view

169. What is the primary advantage of kilovoltage cone-beam CT (kV-CBCT) in radiotherapy?
     A. High soft tissue contrast
     B. Low radiation dose
     C. Setup verification
     D. Real-time imaging
     E. Low cost

170. Which imaging modality is most suitable for delineating prostate tumours in radiotherapy planning?
     A. CT
     B. MRI
     C. PET
     D. 4D-CT
     E. Ultrasound

171. What is the primary source of artefacts in CT imaging?
     A. Photon scattering
     B. Detector efficiency
     C. Metal implants
     D. Reconstruction algorithm
     E. Patient motion

172. Which factor most significantly affects the temporal resolution in MRI?
     A. Field strength
     B. Gradient switching speed
     C. Tube current
     D. Reconstruction algorithm
     E. Field of view

173. What is the primary advantage of perfusion-weighted MRI in oncology?
     A. High spatial resolution
     B. Low radiation dose
     C. Assessment of vascularity
     D. Real-time imaging
     E. Low cost

174. Which imaging modality is most suitable for assessing liver metastases in radiotherapy planning?
     A. CT
     B. MRI
     C. PET
     D. 4D-CT
     E. Ultrasound

175. What is the primary purpose of image segmentation in radiotherapy?
     A. To measure radiation dose
     B. To delineate target volumes
     C. To assess image contrast
     D. To determine spatial resolution
     E. To monitor image noise

176. Which factor most significantly affects the radiation dose in 4D-CT imaging?
     A. Gantry rotation speed
     B. Tube current
     C. Tube voltage
     D. Reconstruction algorithm
     E. Field of view

177. What is the primary advantage of MR spectroscopy in oncology?
     A. High spatial resolution
     B. Low radiation dose
     C. Metabolic profiling
     D. Real-time imaging
     E. Low cost

178. Which imaging modality is most suitable for intrafraction motion monitoring during radiotherapy?
     A. CT
     B. MRI
     C. PET
     D. Fluoroscopy
     E. Ultrasound

179. What is the primary source of contrast in SPECT imaging?
     A. Proton density
     B. Tissue relaxation time
     C. Electron density
     D. Radiotracer uptake
     E. Blood flow

180. Which factor most significantly affects the image noise in PET imaging?
     A. Radiotracer activity
     B. Tube current
     C. Reconstruction algorithm
     D. Field of view
     E. Patient size

Radiation Protection (20 Questions)

181. What is the annual effective dose limit for the lens of the eye for radiation workers in the UK?
     A. 1 mSv
     B. 5 mSv
     C. 20 mSv
     D. 50 mSv
     E. 150 mSv

182. Which material is most effective for shielding beta particles?
     A. Lead
     B. Concrete
     C. Perspex
     D. Boron
     E. Steel

183. What is the primary purpose of the inverse square law in radiation protection?
     A. To maximize radiation dose
     B. To reduce exposure with distance
     C. To measure radiation dose
     D. To calibrate dosimeters
     E. To monitor radiation levels

184. Which factor most significantly affects the public dose in a radiotherapy department?
     A. Beam energy
     B. Bunker shielding
     C. Field size
     D. Gantry angle
     E. Monitor units

185. What is the approximate tenth-value layer (TVL) for a 15 MV photon beam in lead?
     A. 1 cm
     B. 5 cm
     C. 10 cm
     D. 20 cm
     E. 40 cm

186. Which type of personal dosimeter is most suitable for immediate dose readout?
     A. Film badge
     B. TLD
     C. MOSFET
     D. OSL dosimeter
     E. Electronic personal dosimeter

187. What is the primary source of neutron contamination in a radiotherapy treatment room?
     A. Primary beam
     B. Scatter from patient
     C. Photonuclear reactions
     D. Bremsstrahlung radiation
     E. Compton scattering

188. Which regulation governs medical radiation exposure in the UK?
     A. IR(ME)R 2017
     B. IRR 2017
     C. RIDDOR 2013
     D. COSHH 2002
     E. MHRA 2008

189. What is the approximate dose rate reduction factor at 3 meters compared to 1 meter from a point source?
     A. 1/3
     B. 1/6
     C. 1/9
     D. 1/12
     E. 1/18

190. Which factor most significantly affects the shielding requirements for a proton therapy facility?
     A. Beam energy
     B. Field size
     C. Gantry angle
     D. Monitor units
     E. Patient size

191. What is the primary purpose of a supervised area in a radiotherapy department?
     A. To store radioactive sources
     B. To monitor low-level radiation hazards
     C. To restrict public access
     D. To calibrate dosimeters
     E. To perform quality assurance

192. Which material is most effective for shielding high-energy photons?
     A. Lead
     B. Concrete
     C. Water
     D. Boron
     E. Perspex

193. What is the annual effective dose limit for the skin for radiation workers in the UK?
     A. 1 mSv
     B. 20 mSv
     C. 50 mSv
     D. 150 mSv
     E. 500 mSv

194. Which factor most significantly affects the dose to staff during brachytherapy procedures?
     A. Source activity
     B. Shielding placement
     C. Field size
     D. Gantry angle
     E. Monitor units

195. What is the primary advantage of a door interlock system in a radiotherapy bunker?
     A. Reduced construction cost
     B. Prevention of unintended exposure
     C. Increased patient comfort
     D. Simplified quality assurance
     E. Enhanced beam delivery

196. Which type of radiation is most hazardous for internal exposure?
     A. Alpha particles
     B. Beta particles
     C. Gamma rays
     D. Neutrons
     E. X-rays

197. What is the primary purpose of a radiation protection supervisor (RPS) in radiotherapy?
     A. To deliver radiotherapy
     B. To oversee local radiation safety
     C. To calibrate dosimeters
     D. To monitor patient doses
     E. To perform quality assurance

198. Which factor most significantly affects the dose rate from an unsealed radioactive source?
     A. Source activity
     B. Source energy
     C. Source size
     D. Source material
     E. Source shape

199. What is the approximate half-life of Ir-192 used in HDR brachytherapy?
     A. 7 days
     B. 30 days
     C. 74 days
     D. 120 days
     E. 180 days

200. Which principle is most critical for reducing staff dose during radiotherapy procedures?
     A. Time
     B. Distance
     C. Shielding
     D. Optimization
     E. Calibration

Answers

Radiation Physics

101. C. Characteristic X-rays arise from electron ejection from inner shells, followed by orbital transitions.

102. C. Pair production dominates for 15 MV photons in bone due to high energy and Z.

103. D. The HVL for 10 MV photons in concrete is approximately 35 cm.

104. B. Target atomic number most significantly affects bremsstrahlung yield (∝ Z²).

105. B. Collisional interactions dominate for 200 MeV protons, with nuclear interactions secondary.

106. A. Gamma rays have the lowest quality factor (Q=1) in radiation protection.

107. C. K-shell transition in tungsten emits photons of ~60 keV (binding energy).

108. A. Photoelectric effect dominates for 1 keV photons in soft tissue (low energy).

109. A. Elastic scattering (e.g., proton recoil) is the primary interaction for fast neutrons.

110. B. The mass energy absorption coefficient for 1 MeV photons in water is ~0.03 cm²/g.

111. B. Initial energy determines the range of alpha particles (R ∝ E).

112. B. Patient tissues are the primary source of scatter radiation in a treatment room.

113. B. Dose rate from a point source follows D = ΓA / r² (inverse square law).

114. A. Photoelectric effect dominates for 200 keV photons in bone (Z³/E³).

115. C. The range of a 10 MeV electron in tissue is ~5 cm (R ≈ 0.5 E).

116. C. Hydrogen content most affects neutron shielding due to elastic scattering.

117. B. Carbon ions deposit energy primarily via collisional interactions, with high LET.

118. D. Neutrons are effectively shielded by low-Z materials (e.g., hydrogen-rich).

119. C. Photodisintegration in tissue (e.g., O-16) requires ~10 MeV.

120. A. Bremsstrahlung radiation is the primary X-ray source in a diagnostic X-ray tube.

Dosimetry

121. B. The Sievert (Sv) is the SI unit of equivalent dose.

122. A. Absorbed dose (Gy) is most relevant for deterministic effects (e.g., tissue damage).

123. C. The quality factor for fast neutrons is 10 in radiation protection.

124. B. Dose rate for I-131 (Γ ≈ 0.22 R·m²/Ci·h) at 1 m ≈ 0.2 mGy/h for 2 GBq.

125. B. TLDs are suitable for low-dose environmental radiation due to high sensitivity.

126. B. TMR quantifies dose at depth for isocentric setups, accounting for scatter.

127. C. Dmax for a 15 MV photon beam in water is ~3.0 cm.

128. B. Field size significantly affects the scatter factor due to increased scatter.

129. C. Parallel-plate chambers have a small volume, ideal for shallow electron depths.

130. C. Output factor normalizes dose for field size variations.

131. C. Effective dose (Sv) assesses whole-body occupational exposure.

132. B. For neutrons (Q=10), 10 mSv effective dose ≈ 1 mGy absorbed dose (Sv = Gy × Q).

133. D. AAPM TG-61 is suitable for low-energy X-ray dosimetry.

134. D. Calibration stability is the primary uncertainty in MOSFET dosimetry.

135. C. Effective path length corrects for tissue inhomogeneity in MU calculations.

136. B. TLDs are ideal for postal dosimetry audits due to accuracy and stability.

137. C. Collimator scatter factor (Sc) normalizes dose for collimator settings.

138. D. Penumbra width for 15 MV photons at 10 cm depth is ~12 mm.

139. A. Source activity determines the dose rate in HDR brachytherapy.

140. C. Diode detectors offer high spatial resolution for small-field dosimetry.

Radiotherapy Treatment Planning

141. B. Dynamic MLCs modulate beam intensity in IMRT for dose conformity.

142. C. Visible tumour extent (on imaging) defines the GTV.

143. B. Proton therapy’s Bragg peak provides sharp dose fall-off, sparing normal tissue.

144. C. Monte Carlo is most suitable for lung radiotherapy due to heterogeneity handling.

145. B. Tissue compensators correct for surface irregularities in electron therapy.

146. A. Beam energy determines the depth and spread of the Bragg peak in carbon ion therapy.

147. B. SRS delivers high precision for small intracranial targets.

148. B. Anatomical change detection is critical for adaptive radiotherapy.

149. B. Dynamic wedges modulate dose distribution for sloped or uneven surfaces.

150. A. Beam energy determines the depth of dose fall-off in electron therapy.

151. B. Tomotherapy integrates image guidance for precise delivery.

152. B. The rectum is critical for dose constraints in pelvic radiotherapy.

153. B. Beam modifiers optimize dose distribution (e.g., wedges, compensators).

154. A. Beam scattering significantly affects penumbra in proton therapy.

155. B. 4D radiotherapy manages respiratory motion for accurate targeting.

156. C. Tumour motion defines the ITV to account for intrafraction variation.

157. B. Cut-outs shape the radiation field in electron therapy for conformity.

158. A. Dwell time determines dose distribution in HDR brachytherapy.

159. B. CT-guided radiotherapy provides accurate electron density for dose calculation.

160. B. Organ-at-risk dose is critical for NTCP analysis.

Imaging

161. C. MRI provides superior soft tissue contrast for target delineation.

162. B. MRI is suitable for assessing cardiac motion due to high temporal resolution.

163. B. T1-weighted MRI contrast depends on tissue relaxation time (T1 recovery).

164. C. Tube voltage affects contrast resolution in CT by altering photon energy.

165. C. SPECT provides functional information (e.g., perfusion) in oncology.

166. A. Tc-99m is most commonly used in SPECT imaging for oncology.

167. B. Window level adjusts image contrast in CT for visualization.

168. B. Gradient strength most significantly affects MRI spatial resolution.

169. C. kV-CBCT enables setup verification with good bone contrast.

170. B. MRI is ideal for delineating prostate tumours due to soft tissue contrast.

171. C. Metal implants are the primary source of CT artefacts (e.g., streaking).

172. B. Gradient switching speed affects temporal resolution in MRI.

173. C. Perfusion-weighted MRI assesses tumour vascularity.

174. B. MRI is suitable for assessing liver metastases due to high soft tissue contrast.

175. B. Image segmentation delineates target volumes and organs at risk.

176. B. Tube current most significantly affects 4D-CT radiation dose.

177. C. MR spectroscopy provides metabolic profiling of tumours.

178. D. Fluoroscopy enables intrafraction motion monitoring during radiotherapy.

179. D. Radiotracer uptake provides contrast in SPECT imaging.

180. A. Radiotracer activity most significantly affects PET image noise.

Radiation Protection

181. C. The annual effective dose limit for the lens of the eye is 20 mSv for radiation workers.

182. C. Perspex (low-Z) is most effective for shielding beta particles.

183. B. The inverse square law reduces exposure by increasing distance (D ∝ 1/r²).

184. B. Bunker shielding most significantly affects public dose.

185. D. The TVL for 15 MV photons in lead is ~20 cm.

186. E. Electronic personal dosimeters provide immediate dose readout.

187. C. Photonuclear reactions produce neutron contamination in high-energy linacs.

188. A. IR(ME)R 2017 governs medical radiation exposure in the UK.

189. C. Dose rate reduces by 1/9 at 3 m vs. 1 m (inverse square law).

190. A. Beam energy determines shielding requirements for proton therapy (neutron yield).

191. B. Supervised areas monitor low-level radiation hazards.

192. A. Lead is most effective for shielding high-energy photons (high Z).

193. E. The annual effective dose limit for the skin is 500 mSv for radiation workers.

194. B. Shielding placement most significantly affects staff dose in brachytherapy.

195. B. Door interlocks prevent unintended exposure in radiotherapy bunkers.

196. A. Alpha particles are most hazardous for internal exposure due to high LET.

197. B. RPSs oversee local radiation safety compliance.

198. A. Source activity determines the dose rate from unsealed sources.

199. C. The half-life of Ir-192 is ~74 days.

200. B. Distance is critical for reducing staff dose (inverse square law).