LECTURE 5 RT

Multiple Choice Questions (MCQs)

1. The propagation of a photon beam through air or a vacuum follows which law?
- a) Law of Reflection
- b) Inverse Square Law
- c) Law of Refraction
- d) Coulomb’s Law
- Answer: b) Inverse Square Law

2. What additional factors affect a photon beam propagating through a phantom or patient?
- a) Attenuation and scattering
- b) Diffraction and refraction
- c) Reflection and absorption
- d) Ionization and polarization
- Answer: a) Attenuation and scattering

3. The dose distribution in the irradiated volume must be known precisely for:
- a) Image clarity
- b) Successful patient radiation treatment
- c) Enhanced tumor visibility
- d) Increased radiation intensity
- Answer: b) Successful patient radiation treatment

4. The maximum dose occurs at which depth beneath the patient’s surface?
- a) Depth z = 0
- b) Depth z = zmax
- c) Depth z = Dex
- d) Depth z = Ds
- Answer: b) Depth z = zmax

5. Which of the following statements about megavoltage photon beams is correct?

- a) The surface dose is higher than the maximum dose.
- b) The surface dose is generally much lower than the maximum dose.
- c) The surface dose and maximum dose are equal.
- d) The maximum dose occurs on the skin surface.
- Answer: b) The surface dose is generally much lower than the maximum dose.

6. What happens to the surface dose as the photon beam energy increases?
- a) It increases.
- b) It decreases.
- c) It remains the same.
- d) It fluctuates.
- Answer: b) It decreases.
7. The skin sparing effect is significant for which type of beams?
- a) Orthovoltage and superficial beams
- b) Megavoltage beams
- c) Gamma rays
- d) Electron beams
- Answer: b) Megavoltage beams

8. What is used to measure the surface dose (Ds)?

- a) Geiger counter
- b) Thin window parallel-plate ionization chambers
- c) Scintillation counter
- d) Dosimeter badge
- Answer: b) Thin window parallel-plate ionization chambers

9. What is the buildup region in megavoltage photon beams?

- a) The region where the dose decreases exponentially
- b) The region between the surface and the depth of dose maximum
- c) The region at the beam exit point
- d) The region with uniform dose distribution
- Answer: b) The region between the surface and the depth of dose maximum

10. The depth of dose maximum depends primarily on:

- a) Beam field size
- b) Beam energy
- c) Patient weight
- d) Source to surface distance
- Answer: b) Beam energy

11. How does the depth of dose maximum change for fields larger than 5 × 5 cm²?
- a) It increases
- b) It decreases
- c) It remains constant
- d) It fluctuates randomly
- Answer: b) It decreases

12. What term describes the dose delivered to the patient at the beam exit point?
- a) Entrance dose
- b) Surface dose
- c) Buildup dose
- d) Exit dose
- Answer: d) Exit dose
13. In the context of radiation therapy, what does SSD stand for?
- a) Source to Surface Distance
- b) Surface Scatter Dose
- c) Secondary Scattered Dose
- d) Superficial Surface Dose
- Answer: a) Source to Surface Distance

14. What type of beams do not exhibit the skin sparing effect?
- a) Megavoltage beams
- b) Orthovoltage and superficial beams
- c) Gamma beams
- d) Neutron beams
- Answer: b) Orthovoltage and superficial beams

15. What happens to the surface dose with increasing field size?
- a) It increases
- b) It decreases
- c) It remains constant
- d) It fluctuates
- Answer: a) It increases

16. What type of radiation detectors are commonly used in tissue-equivalent phantoms?
- a) Geiger-Müller counters
- b) Scintillation detectors
- c) Ionization chambers
- d) Photographic plates
- Answer: c) Ionization chambers

17. What is the main benefit of the skin sparing effect in radiation therapy?
- a) It reduces overall treatment time
- b) It spares the skin from high doses of radiation
- c) It increases the accuracy of tumor targeting
- d) It enhances image clarity
- Answer: b) It spares the skin from high doses of radiation

18. Which measuring device is oriented towards the source to measure the exit dose?
- a) Thermoluminescent dosimeter
- b) Scintillation detector
- c) Parallel-plate ionization chamber
- d) Photographic film
- Answer: c) Parallel-plate ionization chamber
True/False Questions

1. The inverse square law governs the propagation of a photon beam through a vacuum.
- True

2. In a patient, the photon beam is only affected by the inverse square law.
- False

3. The surface dose is typically higher than the maximum dose for megavoltage photon beams.
- False

4. The surface dose decreases with increasing photon beam energy.

- True

5. The skin sparing effect is significant for orthovoltage beams.

- False

6. The buildup region is the area between the surface and the depth of dose maximum.
- True

7. Depth of dose maximum is primarily dependent on the beam energy.

- True

8. Surface dose increases with the field size.

- True

9. The exit dose is measured at the point where the beam enters the patient.
- False

10. Surface dose includes contributions from high energy electrons produced by photon
interactions in air.
- True

11. For fields smaller than 5 × 5 cm², Zmax is decreases because of collimator scatter effects.
- False

12. Surface dose is measured with scintillation detectors.

- False

13. The skin sparing effect allows for higher doses to be delivered to deep-seated tumors while
sparing the skin.
- True
LECTURE 6 RT
Multiple Choice Questions (MCQs)

1. What does SSD stand for in radiotherapy setups?

- A) Source-to-Scattering Distance
- B) Source-to-Surface Distance
- C) Surface-to-Surface Distance
- D) Surface-to-Detector Distance
- Answer: B

2. What does SAD stand for in radiotherapy setups?

- A) Source-to-Axis Distance
- B) Surface-to-Air Distance
- C) Source-to-Attenuation Distance
- D) Surface-to-Aperture Distance
- Answer: A

3. Which factor is used for SSD dose calculations?

- A) TMR
- B) TPR
- C) PDD
- D) TAR
- Answer: C

4. In a SAD setup, what remains constant?

- A) Source-to-Surface Distance
- B) Source-to-Detector Distance
- C) Source-to-Isocenter Distance
- D) Surface-to-Surface Distance
- Answer: C

5. What primarily influences the shape of the PDD curve?

- A) Field size
- B) Beam energy
- C) Patient thickness
- D) Scatter component
- Answer: B

6. Higher energy beams result in what kind of PDD at high depths?

- A) Lower
- B) Higher
- C) Unchanged
- D) Irregular
- Answer: B
7. What effect does increasing the field size have on the surface dose?
- A) Decreases
- B) Increases
- C) No change
- D) Randomly varies
- Answer: B

8. What is the effect of higher beam energy on surface dose?

- A) Increases it
- B) Decreases it
- C) No effect
- D) Random effect
- Answer: B

9. Which is NOT used for SAD dose calculations?

- A) TAR
- B) TMR
- C) TPR
- D) PDD
- Answer: D

10. Which setup is more common in modern radiotherapy?

- A) SSD
- B) SAD
- C) Both equally
- D) Neither
- Answer: B

11. Which type of field is usually produced with collimators installed in radiotherapy machines?
- A) Circular
- B) Irregular
- C) Rectangular
- D) Elliptical
- Answer: C

12. The buildup region is between which depths in megavoltage photon beams?
- A) Surface and dmax
- B) Surface and exit point
- C) Surface and isocenter
- D) Surface and SSD
- Answer: A
13. Which of the following increases with larger field sizes?
- A) PDD at dmax
- B) Scatter component
- C) Buildup region
- D) Source-to-surface distance
- Answer: B

14. What defines the PDD?

- A) Percentage of surface dose
- B) Percentage of Dmax at different depths
- C) Percentage of exit dose
- D) Percentage of buildup dose
- Answer: B

15. What type of collimators are used to produce circular fields?

- A) Installed collimators
- B) Special collimators
- C) MLCs
- D) Rectangular collimators
- Answer: B

16. What is measured by PDD at d = 0?

- A) Entrance dose
- B) Surface dose
- C) Exit dose
- D) Maximum dose
- Answer: B

17. What does increasing the depth of the prescription point do in an SSD setup?
- A) Decreases distance from the source
- B) Increases distance from the source
- C) No change
- D) Randomly varies
- Answer: B

18. What is the typical value of SSD in SSD setups?

- A) 50 cm
- B) 80 cm
- C) 100 cm
- D) 150 cm
- Answer: C
19. What does increasing the field size do to the collimator factor?
- A) Decreases it
- B) Increases it
- C) No change
- D) Randomly varies
- Answer: B

20. What is the exit dose?

- A) Dose at the beam entry point
- B) Dose at the beam exit point
- C) Maximum dose
- D) Surface dose
- Answer: B

21. Which of the following decreases significantly with beam energy?

- A) Surface dose
- B) PDD at high depths
- C) Maximum dose
- D) Collimator scatter
- Answer: A
True & False Questions

1. SSD setup uses a constant distance between the source and the surface.
- True

2. Higher energy beams result in a higher PDD at high depths.

- True

3. SAD setup is less common in modern radiotherapy.

- False

4. Surface dose decreases with increasing field size.

- False

5. PDD is defined as a percentage of Dmax measured at different depths.

- True

6. TAR is used for SSD dose calculations.

- False

7. Higher energy beams decrease the surface dose.

- True

8. SSD setup uses a constant distance between the source and isocenter.
- False

9. Scatter component decreases with larger field sizes.

- False

10. TMR is used for SAD dose calculations.

- True

11. In an SSD setup, increasing the depth of the prescription point decreases its distance from the
source.
- False