CMD Quality Assurance & Control 3

Question 1

When performing annual QA on a multileaf collimator (MLC), which test specifically evaluates leaf position accuracy under dynamic conditions?

Accepted Answer

Picket fence test

Answer

The picket fence test uses a series of narrow, sequential MLC-defined fields to expose film or an EPID, revealing individual leaf positioning errors under dynamic movement.

Question 2

According to TG-40, how frequently should beam flatness and symmetry be measured for a clinical linear accelerator?

Accepted Answer

Monthly

Answer

TG-40 recommends monthly measurements of beam flatness and symmetry for clinical linear accelerators as part of standard QA protocols.

Question 3

A radiation therapy department uses IMRT for head and neck treatments. Per TG-142, what is the recommended tolerance for IMRT patient-specific QA gamma analysis (3%/3mm)?

Accepted Answer

Greater than 95% of points passing

Answer

TG-142 recommends that IMRT patient-specific QA should achieve greater than 95% of points passing using a 3%/3mm gamma criterion.

Question 4

During a brachytherapy source calibration, the measured air kerma strength deviates by 6% from the vendor-stated value. What is the appropriate action per TG-56?

Accepted Answer

Use the measured value and notify the vendor

Answer

TG-56 states that if the measured source strength deviates by more than 5% from the vendor certificate, the measured value should be used and the discrepancy reported to the vendor.

Question 5

What physical quantity is directly measured by a well-type ionization chamber used in brachytherapy source calibration?

Accepted Answer

Air kerma rate

Answer

A well-type chamber calibrated with a NIST-traceable standard measures air kerma rate, which is then used to determine air kerma strength (SK) for brachytherapy sources.

(CMD) Certified Medical Dosimetrist Practice Test

(CMD) Certified Medical Dosimetrist Practice Test

CMD Quality Assurance & Control 3