Examination Practice Exam Questions

Illinois Medical Dosimetrist Licensing Examination Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following best defines a medical dosimetrist's primary

role?

• Performing surgery
• Administering chemotherapy
• Calculating and planning radiation doses
• Interpreting diagnostic images

Rationale: Medical dosimetrists are responsible for planning and calculating

accurate radiation doses for cancer treatment, ensuring efficacy while minimizing exposure to healthy tissues. 1 / 4

2. In radiation therapy, the term “isocenter” refers to:

• The point of maximum skin dose
• The point on the linear accelerator
• The central point around which the treatment beams are focused
• The position of the tumor on the MRI

Rationale: The isocenter is the fixed point in space that all radiation beams

converge on during treatment.

• Which imaging modality is most commonly used for treatment

planning in radiation therapy?

• Ultrasound

B. PET

• CT scan
• X-ray

Rationale: CT scans provide detailed 3D images of the patient’s anatomy,

which are critical for accurate dose planning.

• What is the primary advantage of intensity-modulated radiation

therapy (IMRT)?

• Reduces treatment time
• Spares healthy tissue while delivering high doses to the tumor
• Uses lower energy radiation
• Requires no patient immobilization 2 / 4

Rationale: IMRT allows precise shaping of radiation beams, minimizing

exposure to surrounding healthy tissue.

5. The unit “Gray (Gy)” measures:

• Radiation exposure in air
• Absorbed dose of radiation
• Radioactivity of a source
• Radiation scatter

Rationale: The Gray measures the amount of radiation energy absorbed per

kilogram of tissue.

6. In dosimetry, “tissue heterogeneity” refers to:

• Patient motion during treatment
• Differences in tissue density affecting radiation absorption
• Variations in machine output
• Treatment field size

Rationale: Different tissues absorb radiation differently; accounting for

heterogeneity is critical for accurate dose calculation.

• Which factor has the greatest influence on photon beam penetration?
• Source-to-surface distance
• Field size
• Photon energy
• Patient position 3 / 4

Rationale: Higher energy photons penetrate deeper into tissue, affecting

dose distribution.

8. The term “beam’s eye view” (BEV) is used to describe:

• The view of the treatment area as seen from the radiation source
• The patient’s perspective
• MRI slice orientation
• The position of shielding blocks

Rationale: BEV helps the dosimetrist visualize how beams intersect the

tumor and surrounding organs.

9. A PTV (Planning Target Volume) accounts for:

• Only the tumor
• Tumor plus margins for motion and setup variability
• Surrounding healthy tissue
• Only critical organs

Rationale: PTV ensures the tumor receives the prescribed dose despite

patient movement and setup uncertainties.

• What is the purpose of a wedge filter in radiation therapy?
• Increase beam energy
• Modify dose distribution across a field
• Protect healthy tissue outside the field
• Measure patient dose
• / 4