ARRT exam prep
ARRT Simulation & Imaging Practice Questions: Free 20-Question Set
Simulation is where the treatment plan is won or lost — and it's heavily tested. These 20 questions cover the full simulation arc: CT simulation workflow, immobilization, target volume margins, motion management, CT imaging fundamentals, and image-guided registration, each with a full explanation.
Want interactive CT anatomy and image matching practice alongside these questions? Rad Therapy Guru packs mock exams, adaptive quizzes, and mastery tracking into one free trial, and it was built by a working therapist and instructor you can read about here.
Section A — CT Simulation & Workflow
Questions 1–4 · answers and explanations included
The primary advantage of CT simulation over conventional fluoroscopic simulation is:
- A.Faster patient throughput with less planning data
- B.True three-dimensional volume data that transfers directly to the treatment planning systemCorrect
- C.A lower cost per patient treated
- D.Elimination of the need for immobilization devices
Answer: B
CT simulation captures a full 3D volume of the patient in treatment position, which transfers to the planning system for dose calculation, contouring, and virtual simulation. Fluoroscopic sim produces 2D projection information only.
The CT scout (topogram) is acquired primarily to:
- A.Replace the full diagnostic CT scan
- B.Set the scan range and verify positioning before the full scan is acquiredCorrect
- C.Measure the patient's total radiation dose
- D.Generate the treatment plan isodose distribution
Answer: B
The low-dose scout images are used to confirm positioning and define the superior-to-inferior scan range before the axial series is acquired. It is a planning aid, not a diagnostic or dosimetric image.
The CT simulator lasers are used to:
- A.Measure the patient's width for the planning system
- B.Mark the isocenter on the patient and create reference tattoosCorrect
- C.Align the gantry with the room axes
- D.Position the detector array for the scan
Answer: B
Room lasers localize a chosen isocenter on the patient's surface, and small permanent tattoos placed at those laser intersections become the daily alignment reference for treatment setup.
Before simulation imaging, a patient of childbearing potential is asked about possible pregnancy. The correct practice is to:
- A.Skip the question unless the patient appears pregnant
- B.Follow the facility's pregnancy screening policy and document the resultCorrect
- C.Assume no pregnancy unless the patient volunteers the information
- D.Refuse to simulate every patient of childbearing age
Answer: B
Facility pregnancy screening policy must be followed before any ionizing radiation procedure, and the screening result is documented in the record. Appearance and assumption are never acceptable screening methods.
Section B — Immobilization & Positioning
Questions 5–8 · answers and explanations included
The primary goal of immobilization in radiation therapy is:
- A.Patient comfort above all other considerations
- B.Reproducibility of the treatment setup at every fractionCorrect
- C.Shorter treatment appointments
- D.Eliminating the need for skin marks
Answer: B
Immobilization exists to reproduce the same precise position at every fraction, which is what allows the planning margins to stay tight. Comfort matters because it supports reproducibility — a comfortable patient holds still better.
A bite block used during head-and-neck simulation primarily:
- A.Keeps the mouth open for easier breathing
- B.Stabilizes the jaw against rotation and can displace the palateCorrect
- C.Protects the teeth from radiation exposure
- D.Replaces the need for a headrest
Answer: B
The bite block fixes the jaw position, preventing rotation of the mandible between simulation and treatment — which would otherwise shift the entire head-and-neck geometry. Some designs also depress the tongue or displace the palate.
Vacuum-lock (vacuum bag) and custom-molded cushions are most useful for:
- A.Reducing setup time only
- B.Preventing rotation and positional errors in head-and-neck and limb setupsCorrect
- C.Replacing daily image verification entirely
- D.Increasing the patient's weight-bearing comfort
Answer: B
Custom vacuum cushions conform to the patient's contour and harden under vacuum, holding rotations and limb positions that flat couches and pillows cannot. They complement, not replace, image guidance.
Prone breast positioning is used in selected patients because it:
- A.Improves coverage of the internal mammary nodes in all patients
- B.Reduces heart and lung dose by letting the breast fall away from the chest wallCorrect
- C.Makes the simulation and setup faster
- D.Increases the depth of the tumor bed
Answer: B
In the prone position the breast falls away from the chest wall, pulling the heart and lung out of the high-dose region — particularly valuable for large-breasted patients. It is a heart-sparing strategy, not a nodal coverage one.
Section C — Target Volumes & Motion Management
Questions 9–12 · answers and explanations included
Four-dimensional CT (4DCT) with respiratory gating is used to:
- A.Shorten the CT scan time
- B.Capture tumor motion through the breathing cycle and define an internal target volume (ITV)Correct
- C.Reduce the CT radiation dose to the patient
- D.Replace the need for immobilization
Answer: B
4DCT resolves the target's position across the respiratory cycle, and the union of positions forms the ITV that the PTV must cover. Motion management like this prevents a geographic miss in mobile thoracic and abdominal targets.
In ICRU target volume nomenclature, moving from GTV to CTV to PTV:
- A.The GTV adds microscopic disease and the CTV adds a setup margin
- B.The CTV adds microscopic disease around the GTV, and the PTV adds a margin for setup uncertaintyCorrect
- C.The PTV adds microscopic disease and the CTV accounts for organ motion only
- D.All three volumes are identical for planning purposes
Answer: B
GTV is the visible tumor; the CTV adds a margin for microscopic spread; the PTV adds a geometric margin covering setup error and intrafraction motion. Getting the sequence of margins right is a classic board question.
Deep inspiration breath hold (DIBH) for left-sided breast treatment:
- A.Increases the cardiac dose
- B.Pulls the heart away from the tangential fields, reducing cardiac doseCorrect
- C.Is used only for right-sided breast treatments
- D.Replaces the need for lung sparing techniques
Answer: B
During deep inspiration the diaphragm descends and the heart moves inferiorly and away from the tangential breast fields, lowering cardiac dose. DIBH is the standard heart-sparing motion strategy for left breast irradiation.
The choice between arterial and venous phase IV contrast during CT simulation matters because:
- A.Arterial phase is always used for every tumor site
- B.Contrast timing changes how the target and organs at risk are visualizedCorrect
- C.Venous contrast is never used in radiation oncology
- D.The phase choice alters the dose calculation algorithm
Answer: B
Arterial and venous phases enhance different structures at different times, and the phase must match what the contouring needs — for example, arterial enhancement for some liver targets. The dose calculation itself still treats contrasted tissue carefully, but visualization is what the timing choice controls.
Section D — CT Imaging & Visualization
Questions 13–16 · answers and explanations included
On a CT image, the approximate Hounsfield unit values of water, air, and dense cortical bone are:
- A.Water 0, air −1000, dense bone about +1000Correct
- B.Water +1000, air 0, dense bone −1000
- C.Water 0, air +1000, dense bone −1000
- D.Water −1000, air 0, dense bone +1000
Answer: A
The Hounsfield scale is anchored at water = 0 with air at −1000; dense cortical bone sits near +1000. These anchors appear constantly in CT questions and in heterogeneity correction discussions.
Adjusting the window and level settings on a CT display:
- A.Changes the displayed contrast, not the underlying acquired dataCorrect
- B.Alters the Hounsfield values stored in the image
- C.Corrects for CT number artifacts
- D.Changes the slice thickness of the scan
Answer: A
Window/level is a display mapping: it stretches or centers the gray scale over a chosen range of Hounsfield units. The acquired data never change — a common distractor on imaging questions.
MRI is often fused with the planning CT because it:
- A.Provides better dose calculation than CT
- B.Offers superior soft-tissue contrast for targets such as brain and head-and-neck tumors, while the CT remains the dose-calculation baseCorrect
- C.Eliminates the need for a planning CT scan
- D.Reduces treatment planning time by half
Answer: B
MRI excels at soft-tissue contrast, improving GTV and OAR delineation in brain, head-and-neck, and soft-tissue targets. Because MR geometric and density information are not dose-calculation ready, the CT remains the physical basis for planning.
A digitally reconstructed radiograph (DRR) is:
- A.A radiograph taken with the treatment beam on
- B.A computed radiograph reconstructed from the planning CT, compared against port films or EPID imagesCorrect
- C.A fluoroscopic image of the treatment field in real time
- D.The planning system's printed dose distribution
Answer: B
A DRR is a simulation of a planar radiograph computed from the CT dataset at the beam's eye view. It is the reference image against which treatment port films and EPID images are compared for setup verification.
Section E — Image Guidance & Registration
Questions 17–20 · answers and explanations included
Permanent tattoos are preferred over ink skin marks for daily treatment alignment because they:
- A.Are larger and easier to see at a distance
- B.Do not wash off or fade mid-treatment courseCorrect
- C.Hurt less when applied
- D.Can be removed at the end of treatment
Answer: B
Ink marks smudge or wash away with daily hygiene, and a lost mark means alignment is improvised — exactly the failure mode tattoos prevent. Tattoos are permanent, which is precisely why they are the reliable daily reference.
For prostate image-guided alignment, matching on pelvic bones alone can miss target shifts because:
- A.The prostate never moves relative to the pelvic bones
- B.Prostate position varies relative to bony anatomy, so soft-tissue or seed matching is preferredCorrect
- C.Bones are too low in contrast to match reliably
- D.Seed matching is prohibited by regulation
Answer: B
Rectal and bladder filling shift the prostate relative to the bony pelvis, so bone-only matching can show a perfect alignment while the target itself is displaced. Daily soft-tissue matching or seed-based alignment corrects for that internal motion.
PET-CT images are registered with the planning CT primarily to:
- A.Replace the planning CT for dose calculation
- B.Use FDG-avid, metabolically active volumes to help define the GTV — with registration accuracy carefully verifiedCorrect
- C.Reduce the CT simulation appointment time
- D.Measure the patient's daily positioning error
Answer: B
PET shows metabolic activity that CT may not resolve, refining the GTV especially in nodal and lung disease. Fusion accuracy limits its value, so registration is verified; PET is never the dose-calculation dataset.
Transabdominal ultrasound (BAT-style) localization in prostate radiotherapy is used to:
- A.Align the prostate target daily before treatment without additional ionizing radiationCorrect
- B.Measure the bladder volume after treatment
- C.Replace the planning CT
- D.Image the prostate only during seed implant surgery
Answer: A
BAT-style ultrasound aligns the prostate against the planning CT reference each day before treatment, adding no extra imaging dose. It was an early daily prostate localization method, later supplemented by CBCT and fiducial approaches.
How Did You Do?
Score yourself one point per correct answer, then act on your band:
17–20 correct
You are in strong shape.
You are close to exam-ready. Identify your weakest category above and drill it until every explanation feels routine — then keep up timed practice sets.
12–16 correct
Solid foundation.
You know the fundamentals but have gaps. Rebuild the categories where you missed the most questions, then retake this set in a week and confirm the score holds.
Under 12
Study by category.
Map every miss to the ARRT content outline — simulation workflow, immobilization, target volumes, CT imaging, and image guidance — and study one category at a time, starting with your weakest.
Get the printable Dosimetry Cheat Sheet (PDF)
Simulation feeds the planning numbers — grab the free printable dosimetry cheat sheet with your email and it downloads instantly.
Ready for the full study suite?
These 20 questions are a taste of the practice materials inside Rad Therapy Guru: timed mock exams, adaptive quizzes, flashcards, and mastery tracking across every ARRT topic.
ARRT Simulation & Imaging Practice Questions FAQ
What is a CT simulation?
CT simulation is the planning scan session where the patient is positioned with immobilization devices, scanned, and marked with reference tattoos and a defined isocenter. The CT dataset becomes the basis for dose calculation and the entire treatment plan.
What happens at a simulation appointment?
The therapist positions the patient, fabricates or adjusts immobilization devices, acquires the planning CT (sometimes with contrast or motion management such as breath hold), marks reference points with the lasers, and schedules the first treatment.
Does simulation hurt?
No. Immobilization devices and CT scanning are painless; the discomfort is usually holding still or the contrast injection, not the scan itself. Patients with claustrophobia should tell the team in advance so comfort measures can be planned.
How long does a CT simulation take?
Most CT simulations take about 30–60 minutes from positioning to marking, though complex setups — head and neck with custom immobilization, for example — can take longer.
More free practice sets
MDCB practice questions
20 free CMD exam questions with explanations.
ARRT patient care questions
Positioning, communication, consent, and safety.
ARRT physics questions
MU calculations, inverse square, PDD and TMR, wedges.
ARRT brachytherapy questions
LDR and HDR, isotopes, applicators, regulations.
ARRT QA & safety questions
Daily QA, dosimetry, regulations, protection.
Free dosimetry cheat sheet
Printable PDF of every formula and quick-lookup table.
Content reviewed by Kate, a working radiation therapist and instructor — see the full story on the about page.