CAMRT RTR Exam common mistakes
CAMRT RTR Exam · Understand the traps and how to avoid them.
On image-evaluation items the candidate jumps straight to a technical-factor change (usually 'increase mAs') that would correct the appearance of the image, without first naming what is actually wrong with it.
Clinical habits are built around brightness control, so 'too light = more mAs' becomes a reflex; the exam instead tests whether the candidate can separate exposure error from scatter, motion, processing and positioning error, and each has a different correction.
What to do instead
Before touching the answer options, write one word on the scratch sheet classifying the fault: exposure, scatter, motion, processing, or positioning. Only then look for the option that addresses that category - if the image is grey and noisy from scatter, adding mAs makes it worse, not better.
Mixes occupational and public dose limits, and applies whole-body numbers to the lens of the eye, skin or extremities.
The numbers are memorized as a flat list rather than as a structure (who / which tissue / per what period), so under exam pressure the wrong cell of the table is recalled.
What to do instead
Rebuild the table from the current CNSC regulations during study as a grid of person category (worker, public, student under 18) against tissue (whole body, lens, skin/extremities), and note the period each limit is averaged over. Anchor with two firm numbers - occupational whole-body 50 mSv in a year, public 1 mSv in a year - and derive the rest from the table.
Treats dose or intensity as changing linearly with distance, or forgets that changing SID requires a compensating mAs change.
Candidates remember 'farther means less dose' but drop the square from the relationship, and distance-based mAs compensation is rarely calculated by hand in daily practice because equipment or charts handle it.
What to do instead
Write the identity before substituting anything: I1 x d1 squared = I2 x d2 squared, and mAs1/mAs2 = d1 squared/d2 squared. Square the distance ratio as a separate line of working, then apply it, so an un-squared ratio can never reach the answer.
Accepts a patient's report that an implant is 'MRI safe', or a generic safety label, as clearance without working through the conditional parameters for the specific scan described.
In a real department the implant check is often completed by someone else on a form, so the candidate never practises the reasoning that the exam is actually testing - that 'conditional' means safe only within stated limits.
What to do instead
Apply a fixed three-part check to every device item: (a) is the label MR-unsafe, MR-safe or MR-conditional; (b) if conditional, does this scenario meet every stated condition (static field strength, SAR or dB/dt limit, coil type, scan duration, body region); (c) which mechanism is the concern - displacement, RF heating or artefact. If any stated condition is unmet, the device is not cleared.
Identifies sequence weighting from one conspicuous feature, such as bright CSF meaning 'it must be T2', instead of from the timing parameters plus a second reference tissue.
Recognition is taught visually from sample images, and CSF is the most memorable landmark, but many sequences (FLAIR, steady-state, post-contrast, fat-suppressed) deliberately break the simple rule.
What to do instead
Read TR and TE first and place the sequence in the 3-cell grid - long TR with long TE is T2-weighted, long TR with short TE is proton density, short TR with short TE is T1-weighted. Then confirm with a second tissue (fat is bright on T1 and on non-fat-suppressed T2; fluid is dark on T1 and FLAIR). If the two checks disagree, the sequence is a variant and the timing parameters win.
Miscalculates the number of half-lives in a decay problem, most often by subtracting the elapsed time from the half-life, or by leaving time units mismatched; then rounds intermediate values so the result matches no offered option.
The formula is recalled as a whole rather than as two steps, and decay problems are one of the few places on the exam where a single arithmetic slip removes all four options.
What to do instead
Write n = t / T-half-life as a separate fraction with units cancelled before any arithmetic, then halve the activity n times (or use A = A0 x e to the minus 0.693n). Carry at least three significant figures through the working and round only at the end; if the answer is not among the options, re-check n first, not the arithmetic.
Treats radionuclide purity, radiochemical purity and chemical purity as interchangeable terms, and cannot say what test measures each.
The words look similar and are frequently used loosely in conversation, so they are memorized as a list of words rather than as three distinct questions about the same sample.
What to do instead
Attach each term to one question and one test: radionuclide purity - how much of the activity comes from the intended radionuclide (gamma spectroscopy; e.g. the molybdenum-99 breakthrough limit of 0.15 kBq Mo-99 per MBq Tc-99m), radiochemical purity - how much of the activity is in the desired chemical form (chromatography), chemical purity - how much non-radioactive contaminant is present.
Applies percentage depth dose to an isocentric calculation, or applies TMR to a setup in which the source-to-surface distance changes between fields.
Candidates select the equation by what the question seems to be about (depth, dose) rather than by the geometry of the setup, and PDD is the formula most recently practised.
What to do instead
Write the setup type - SSD or SAD - at the top of the working before choosing an equation. SSD-based fixed-distance setups use PDD, with an inverse-square correction if the distance changes; isocentric setups use TMR, which is independent of SSD. Then check that every factor in the equation has a matching given value.
Mixes gray and centigray during dose and fractionation arithmetic, and confuses total course dose with dose per fraction.
The factor of 100 is applied inconsistently, and fractionation questions are read quickly because the numbers look simple, so the wrong quantity is multiplied or divided.
What to do instead
Write 'cGy = Gy x 100' at the top of the scratch sheet and label every number with its unit as it is extracted from the question. Close the calculation with the identity total dose = dose per fraction x number of fractions, and check the answer against that identity before selecting an option.
In a contrast-reaction scenario, selects an antihistamine and observation for a severe anaphylactoid reaction, or delays treatment while deciding whether the reaction is truly allergic.
Mild urticaria is the reaction candidates have actually seen and managed, and the drug names are learned as a group rather than tied to severity, so the moderate-to-severe pathway is never rehearsed.
What to do instead
Learn the reaction by severity tier and attach one drug to each: mild urticaria - observe, antihistamine if needed; bronchospasm - oxygen plus inhaled beta-2 agonist; laryngeal oedema or hypotension - intramuscular epinephrine, oxygen, IV fluids and call for help immediately. Practise the severe tier as a script so the first action is never a diagnostic pause.