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RD3.1-4 | Radiation Safety and Legal Requirements — Practice Quiz
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A radiology resident is asked to classify the biological effects of ionising radiation. Which of the following is the defining feature of a STOCHASTIC effect such as radiation-induced carcinogenesis?
Correct. Stochastic effects (cancer, hereditary effects) are assumed to have no threshold under the linear-no-threshold model; dose changes the probability of the effect, while its severity, if it occurs, is independent of dose.
Stochastic = no threshold, dose changes probability (cancer, hereditary). Deterministic = threshold, dose changes severity (cataract, erythema, sterility, ARS).
Stochastic effects are no-threshold, probability-driven late effects. A threshold and dose-dependent severity define DETERMINISTIC (tissue-reaction) effects.
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Which one of the following radiation effects is a DETERMINISTIC (non-stochastic / tissue-reaction) effect?
Correct. Cataract is a classic deterministic effect: it occurs only above a threshold dose and its severity increases with dose. Skin erythema, sterility and acute radiation syndrome are the other typical examples.
Deterministic effects with thresholds: cataract, skin erythema, sterility, acute radiation syndrome. All cancers and hereditary effects are stochastic.
Carcinogenesis (leukaemia, solid tumours, thyroid cancer) and heritable mutations are STOCHASTIC. Cataract is the deterministic effect in this list.
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A CT technologist's monthly exposure report quotes an EFFECTIVE DOSE. Which unit is the correct one for effective (and equivalent) dose, reflecting biological harm?
Correct. Equivalent and effective dose, which weight absorbed dose for radiation type and tissue sensitivity to express biological harm, are measured in sieverts (Sv).
Absorbed dose = Gray (Gy); equivalent and effective (biological) dose = Sievert (Sv); activity = Becquerel (Bq).
The gray (Gy) measures ABSORBED dose (energy deposited per unit mass). Biological/effective dose is in sieverts (Sv). Becquerel measures activity.
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Which device is the standard PRIMARY personnel dosimeter used to monitor the cumulative occupational radiation exposure of a radiology worker over a monitoring period?
Correct. The thermoluminescent dosimeter (TLD) badge is the primary personnel dosimeter: it accumulates dose over the wear period and is read out periodically to record each worker's cumulative exposure.
TLD = primary personnel dosimeter for cumulative occupational dose. Survey meters measure area dose rate, not individual cumulative exposure.
GM survey meters and ionisation chambers measure area/real-time rates, not cumulative personal dose. The TLD badge is the standard personal cumulative dosimeter.
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ALARA is best described as which element of the radiation-protection framework, and which set of practical methods achieves it?
Correct. ALARA (As Low As Reasonably Achievable) is the OPTIMISATION principle. The three practical methods (the protection triad) that achieve it are minimising time, maximising distance, and using shielding.
Three ICRP principles: justification, optimisation (= ALARA), dose limitation. ALARA is achieved by time, distance, shielding.
ALARA is the optimisation principle, not a fixed dose limit. It is delivered through the triad of time, distance and shielding.
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A radiographer doubles her distance from a point source of scattered radiation during a fluoroscopy procedure. By the inverse-square law, the dose rate she receives changes to approximately what fraction of the original?
Correct. The inverse-square law means intensity falls with the square of distance. Doubling distance gives 1/2-squared = 1/4 of the original dose rate, which is why distance is such a powerful protection lever.
Inverse-square law: dose rate is proportional to 1/distance-squared. Doubling distance quarters the dose rate; distance is the most effective of the ALARA methods.
Intensity is inversely proportional to the square of distance. Doubling distance reduces dose rate to (1/2)-squared = one-quarter, not one-half.
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Which statutory body is the regulatory authority responsible for radiation safety in India under the Atomic Energy Act 1962, with power to enforce dose limits and authorise X-ray installations?
Correct. The AERB, constituted under the Atomic Energy Act 1962, is India's statutory radiation regulator. The ICRP only issues advisory recommendations; it has no enforcement power.
AERB (Atomic Energy Act 1962) = Indian statutory regulator with enforcement power. ICRP = international advisory body only.
The ICRP is advisory only. India's enforcing regulator is the AERB, established under the Atomic Energy Act 1962.
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Under the PC-PNDT Act 1994, which of the following is the central PROHIBITION the Act is designed to enforce?
Correct. The PC-PNDT Act prohibits prenatal sex determination and the communication of foetal sex by words, signs or any manner, in order to prevent sex-selective abortion. Diagnostic ultrasound itself remains permitted for genuine medical indications.
PC-PNDT Act 1994 prohibits prenatal sex determination and disclosure of foetal sex; it mandates registration, Form F record-keeping and bans advertising of sex-determination services.
The Act does not ban prenatal imaging for medical reasons; it bans the determination or disclosure of foetal sex. Dose limits and dosimetry are matters for the AERB, not PC-PNDT.
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