Radiobiology, Radiation Protection, and Imaging Science and Informatics

What is the principal radiation interaction in the human body?

Radiolysis of water

Which phase of the cell cycle is most radiosensitive?

M

What is the main toxic product formed from the radiolysis of water?

Hydrogen peroxide

What cellular effect is most likely caused by a dose of 1000 Gyt?

Instant cell death

What is the unit used to express Linear Energy Transfer (LET)?

keV/μm

Which syndrome is associated with a dose of 4–8 Gyt?

Hematologic

Why are fetus and neonates more radiosensitive than adults?

Due to high rate of cell division

Which of the following statements about LET is correct?

High LET causes greater biological damage

What is the main factor that distinguishes deterministic from stochastic effects?

Severity dependence on dose

What occurs when free radicals produced during radiolysis interact with DNA?

DNA strand breaks and mutations

Which macromolecular effect is characterized by decreased viscosity?

Main-chain scission

The increase in cases correlates with cumulative dose but not with severity. What does this describe?

Linear non-threshold model

Which of the following are late effects of radiation exposure?

1. Cataract formation

2. Fibrosis

3. Leukemia

4. Infertility

All of the above

During which of the following subphases of meiosis do the chromosomes appear and line up along the equator of the nucleus?

Metaphase

Which dose range, applied to both ovaries, is needed to induce permanent sterility?

300-800 rad

The latent period of radiation-induced leukemia is considered to be:

4-7 years.

A patient receives an absorbed dose of 1 Gy from x‑rays to the lungs. What is the effective dose?

0.12 Sv

A radiation oncologist is treating a tumor with a choice of two types of radiation, photon radiation (X-rays) with a required dose of 60 Gy to achieve tumor control, and proton therapy, which has an RBE of 1.5. What dose of proton therapy is needed to achieve the same biological effect as 60 Gy of X-rays?

40 Gy

During a radiation accident, a worker receives an absorbed dose of 1.5 Gy and an equivalent dose of 2 Sv. The affected organ is the gonads. What is the effective dose?

0.15 Sv

What implications do stochastic effects have for the safety protocols in pediatric radiology?

Protocols should be stricter to minimize radiation doses.

In the context of radiation protection, how is the principle of ALARA (As Low As Reasonably Achievable) justified by the nature of stochastic effects?

It is based on reducing the probability of stochastic effects.

If an organ receives an absorbed dose of 2 Gy and has a mass of 1.5 kg, how much energy was absorbed?

3 J

What unit is used to measure effective dose in radiation protection?

Sievert

What is the standard dose limit for occupational exposure per year?

50 mSv

What is the recommended monthly dose limit for the embryo-fetus of a pregnant worker?

0.5 mSv

Which principle focuses on reducing exposure to ALARA levels?

Optimization

What is the tissue dose threshold for the lens of the eye in radiation workers per year?

150 mSv

Which standard is the foundation of modern radiation protection practice?

Linear-nonthreshold dose response

The System of Dose Limitation is primarily designed to:

Control radiation exposure and manage risk

Which effect is characterized by a threshold dose and severity that increases with dose?

Deterministic effect

Which of the following is NOT one of the three core principles of the System of Dose Limitation?

Standardization

Dose limits are primarily intended to apply to:

Radiation workers and the public

Why is ALARA considered a guiding philosophy rather than a numerical rule?

It evolves with evidence and technology

Which practice BEST reflects occupational optimization?

Using time, distance, and shielding during fluoroscopy

A radiology department adopts pulsed fluoroscopy and filtration. Which ALARA factor is MOST directly addressed?

Dose reduction technology

A student claims that staying below dose limits guarantees safety. Why is this reasoning flawed?

Dose limits eliminate stochastic effects

Why does the System of Dose Limitation emphasize preventing deterministic effects?

They have clear dose thresholds

Which statements about dose limits are TRUE?

1. Prevent deterministic effects

2. Apply to patients

3. Limit stochastic risk

4. Apply to workers and public

2 and 4

Why is optimization considered the most dynamic principle of dose limitation?

It changes with technology and practice

Which detector directly measures exposure in roentgens?

Ionization chamber

Which detector uses electron-hole pair formation as its detection mechanism?

Semiconductor detector

What is the approximate energy required to create an electron-hole pair in semiconductors?

2–3 eV

Why are semiconductor detectors more efficient than gas-filled detectors?

They require less energy to free electrons

Which statement BEST explains why Geiger- Muller counters cannot distinguish radiation energies?

They produce ion pairs beyond delta particles

In scintillation detectors, what is the role of the photomultiplier tube (PMT)?

Converts light photons into electrical signals

A nuclear medicine technologist needs to measure the activity of Tc-99m before injection. Which device should be used?

Dose calibrator

A radiologic technologist wants to detect radioactive contamination on a surface. Which device is MOST appropriate?

GM counter

Which semiconductor detector is needed for SPECT imaging in Nuclear Medicine with good energy resolution and room temperature. operation. Which is BEST?

CZT

What is the primary material used in OSL dosimeters?

Aluminum oxide

What is the MOST important component of a TLD badge?

Thermoluminescent crystal

What is the usual placement of a dosimeter for whole-body exposure?

Chest or collar level

Why is the light emitted from a TLD proportional to radiation dose?

Due to trapped electrons

A dosimeter needs to measure deep dose vs skin dose. Which component enables this?

Filters

A TLD crystal is heated in a reader. What is being measured?

Light emitted

Which statements are TRUE regarding film badge?

1. Sensitive to heat and humidity

2. Provides instantaneous reading

3. Has limited shelf life

1 and 3

Compare TLD and OSL: which is CORRECT?

1. Both use trapped electrons

2. TLD uses heat, OSL uses laser

3. OSL uses sodium iodide

1 and 2

A department follows ICRP recommendations even when local regulations are less strict. This reflects:

Conservative radiation-protection philosophy

Which of the following BEST describes the fundamental principle of radiation detection?

Radiation causes excitation,  producing a measurable signal

A facility uses a double dosimeter system. Where should the second badge be placed?

Inside apron at chest/waist

A technologist accidentally leaves their dosimeter in an X-ray room overnight. What is the MOST likely consequence?

False high exposure reading

A dosimeter needs to measure deep dose vs skin dose. Which component enables this:

Filters

A technologist places the badge inside the apron instead of outside (single badge system). Evaluate.

Incorrect, underestimates exposure.

A facility wants permanent legal records of exposure. Which is BEST:

Film badge

A damaged dosimeter is still used for monitoring. Evaluate.

Incorrect due to inaccurate measurements

A system has poor reproducibility but good linearity. Evaluate.

Inconsistent output despite correct proportionality

A fluoroscopy system operates at 150 mGy/min without special control. Evaluate.

Exceeds standard limits

Increasing kVp may reduce patient dose primarily because it allows:

Reduced mAs

Which technique improves image quality by enhancing contrast resolution while also reducing effective dose?

Proper collimation

Which statements are consistent with mammography dose principles?

1. ESE may be approximately 8 mGy per view.

2. Glandular dose is approximately 15% of ESE.

3. Routine screening should only be two projections.

4. Lowering technique to 26 kVp is recommended to improve acceptability.

1 and 3 only

A patient is positioned for an upper extremity examination while seated. Which

radiation protection action is MOST appropriate?

Shield the gonads and position the patient lateral to the useful beam.

A pregnant patient requires an x-ray examination where the fetus is not in or near the primary beam. Which approach is MOST appropriate?

Use pelvic shielding, precise collimation, and careful positioning.

A patient was unknowingly exposed during early pregnancy. What is the BEST first step?

Estimate fetal dose by a medical physicist.

Which are appropriate safeguards against accidental irradiation during pregnancy?

1. Asking whether the patient is or could be pregnant

2. Asking the date of the last menstrual period

3. Posting pregnancy warning signs in waiting areas

4. Ignoring pregnancy status after two months

1 and 3 only

A fetus receives less than 100 mGy from diagnostic exposure. Which decision is most consistent with the reference?

Therapeutic abortion is not indicated.

Which statement BEST describes the first two weeks of pregnancy after irradiation?

Irradiation is least hazardous, and resorption may occur.

A referring physician uses ACR Appropriateness Criteria to select imaging for a specific clinical condition. What is the PRIMARY benefit?

It assists appropriate imaging decisions and dose management.

Which statements correctly describe relative radiation level concepts?

1. Ultrasound and MRI are assigned zero because no ionizing radiation is involved.

2. Pediatric dose estimate ranges are lower than adult ranges.

3. Radiation symbols indicate relative radiation intensity.

4. PET-CT is lower than radiography in the order.

1 and 3 only

Scenario: A CT unit operates 6 days/week. It performs: 22 routine CT patients/day, 85 slices each, 200 mAs/slice 8 CTA patients/day, 160 slices each, 350 mAs/slice. A wall beside the gantry is adjacent to a public corridor located 3.2 m from isocenter. The physicist estimates that 35% of the total workload contributes to this wall. The HVL of the shielding material is 4.5 mm Pb.

What is the weekly workload W?

82,200 mA-min/week

Scenario: A CT unit operates 6 days/week. It performs: 22 routine CT patients/day, 85 slices each, 200 mAs/slice 8 CTA patients/day, 160 slices each, 350 mAs/slice. A wall beside the gantry is adjacent to a public corridor located 3.2 m from isocenter. The physicist estimates that 35% of the total workload contributes to this wall. The HVL of the shielding material is 4.5 mm Pb.

What occupancy factor T is appropriate for the public corridor?

0.2

Scenario: A CT unit operates 6 days/week. It performs: 22 routine CT patients/day, 85 slices each, 200 mAs/slice 8 CTA patients/day, 160 slices each, 350 mAs/slice. A wall beside the gantry is adjacent to a public corridor located 3.2 m from isocenter. The physicist estimates that 35% of the total workload contributes to this wall. The HVL of the shielding material is 4.5 mm Pb.

Calculate the transmission factor B.

3.56 x 10-5

Scenario: A CT unit operates 6 days/week. It performs: 22 routine CT patients/day, 85 slices each, 200 mAs/slice 8 CTA patients/day, 160 slices each, 350 mAs/slice. A wall beside the gantry is adjacent to a public corridor located 3.2 m from isocenter. The physicist estimates that 35% of the total workload contributes to this wall. The HVL of the shielding material is 4.5 mm Pb.

What percentage of radiation is allowed to pass through?

0.00356%

Scenario: A CT unit operates 6 days/week. It performs: 22 routine CT patients/day, 85 slices each, 200 mAs/slice 8 CTA patients/day, 160 slices each, 350 mAs/slice. A wall beside the gantry is adjacent to a public corridor located 3.2 m from isocenter. The physicist estimates that 35% of the total workload contributes to this wall. The HVL of the shielding material is 4.5 mm Pb.

How many HVLs are required?

15 HVLs

Scenario: A CT unit operates 6 days/week. It performs: 22 routine CT patients/day, 85 slices each, 200 mAs/slice 8 CTA patients/day, 160 slices each, 350 mAs/slice. A wall beside the gantry is adjacent to a public corridor located 3.2 m from isocenter. The physicist estimates that 35% of the total workload contributes to this wall. The HVL of the shielding material is 4.5 mm Pb.

What barrier thickness is required?

67.5 mm Pb

A newly installed PACS workstation boots normally but fails to communicate with the hospital network. The Ethernet cable is intact and functioning when tested on another computer. Which hardware component should the biomedical engineer inspect FIRST?

Network Interface Card (NIC)

A technologist accidentally disconnects the power from a workstation while editing a radiology report. After restarting the computer, all unsaved work is lost, but the operating system starts normally. Which statement BEST explains this observation?

RAM is volatile memory, whereas ROM retains essential startup instructions.

Four technologists discuss computer memory. Which technologist made the INCORRECT statement?

Technologist I: RAM requires continuous electrical power to retain data.

Technologist II: ROM stores the instructions needed to initialize the computer.

Technologist III: Increasing ROM capacity improves multitasking performance during image processing.

Technologist IV: RAM allows rapid manipulation of multiple diagnostic images.

Technologist III

During a routine CT examination, the scanner successfully transmits images to the PACS server located in another hospital building. The network administrator determines that the image packets are successfully leaving the CT suite but cannot reach the remote network because the device responsible for forwarding packets between different networks has failed. Which network component is MOST likely malfunctioning?

Router

A PACS workstation can communicate with other computers within the radiology department but cannot access the hospital's Electronic Medical Record (EMR) system located in another building. Which network device should the IT engineer investigate FIRST?

Router

A radiologist working from home securely accesses the hospital PACS through an encrypted connection that allows communication over the public internet while maintaining patient confidentiality. Which technology BEST enables this connection?

VPN

Four students discuss networking devices. Which student made the INCORRECT statement?

Student I: A switch forwards data to the correct device within the same local network.

Student II: A router connects different networks by directing packets between them.

Student III: A firewall primarily accelerates image transmission by increasing bandwidth.

Student IV: A VPN creates an encrypted communication tunnel over the internet.

Student III

A hospital plans to connect twenty PACS workstations, three CT scanners, two MRI units, and several reporting stations within a single radiology department. The administrator wants the highest possible speed at the lowest installation cost. Which network classification is MOST appropriate?

LAN

A biomedical engineer explains that every PACS workstation has both an IP address and a MAC address. Which statement BEST distinguishes these two identifiers?

IP addresses identify the logical network location of a device, whereas MAC addresses identify the physical network interface.

A CT scanner transmits images to the PACS server. Within the local radiology network, the switch forwards Ethernet frames using the destination network interface rather than the logical network location. Which address does the switch primarily examine?

MAC Address

A radiologist accesses a web-based PACS viewer through the following address: Which statement BEST explains the primary advantage of using HTTPS instead of HTTP?

HTTPS encrypts communication, helping preserve confidentiality  integrity, and server authentication.

A technologist uses AirDrop to send a teaching file containing anonymized radiographs to another workstation. During transmission, the file is divided into smaller units, delivered reliably, and reassembled correctly before being opened. According to the OSI model, which layer is PRIMARILY responsible for these functions?

Transport Layer

A CT examination has been successfully transmitted to the PACS. Before deleting the local copy from the modality workstation, the technologist waits for confirmation that the archive has permanently stored the study. Which DICOM service provides this confirmation?

Storage Commitment

Four radiologic technologists discuss DICOM. Which technologist made the INCORRECT statement?

Technologist I: DICOM standardizes both medical image format and communication between imaging devices. Technologist II: DICOM enables interoperability among equipment from different manufacturers. Technologist III: DICOM primarily manages appointment scheduling and billing. Technologist IV: DICOM stores imaging parameters together with patient information.

Technologist III

A hospital information system sends a newly requested CT examination to the Radiology Information System without transmitting any image data. The message contains patient demographics, physician orders, and scheduling information. Which communication standard is MOST appropriate for this exchange?

HL7

A hospital administrator asks the chief radiologic technologist to distinguish the primary functions of several information systems. Which pairing is MOST accurate?

RIS — Workflow management; PACS — Image management; HIS — Hospital- wide patient information

A patient arrives at the Emergency Department after a motor vehicle collision. The physician orders a CT scan electronically. Patient information is transferred to the Radiology Information System, the examination automatically appears on the CT console, images are acquired and archived, the radiologist completes the interpretation remotely, and the final report becomes immediately available in the patient's electronic  medical record. Which sequence BEST represents the technologies that make this workflow possible?

HIS → HL7 → RIS → DICOM Modality Worklist → CT Acquisition → DICOM Storage to PACS → PACS Viewer → HL7 Report Distribution to HIS/EMR