During monthly quality assurance, output lands inside the department's tolerance, the light and radiation field edges agree, and the MLC leaves verify, but the sagittal isocenter laser sits about 3 mm off the mechanical isocenter. Which corrective action is justified before the next patient is set up?
Select an answer to reveal the explanation.
Short Explanation
You can focus on the one finding that is out of tolerance: the sagittal isocenter laser is off the mechanical isocenter. Correct that reference by realigning the laser and verifying it; changing output, the light field, or MLC leaves would address checks that passed. You’ll have the laser checked before the next patient is set up.
Full Explanation
Isocenter lasers provide the daily alignment reference, so a sagittal laser that sits about 3 mm off the mechanical isocenter means setups in that plane are being registered to the wrong point until the drift is corrected. Realigning the laser to the mechanical isocenter and confirming it with the standard isocenter check restores the reference used to position the couch and patient, and addresses the only failed finding in this survey. Re-running output calibration against the reference chamber is not justified when output is within tolerance; changing a verified baseline could create an error where none existed. Adjusting the light field mirror and bulb is also unwarranted because the light and radiation field edges already agree, so that work could introduce a mismatch rather than correct one. Recalibrating MLC leaf positions against the imaging panel targets leaves that have verified correctly and risks moving them out of tolerance. The exam caveat is to interpret quality assurance findings together: intervention is warranted for the component that is out of tolerance, not for checks that pass. A practical check is to repeat the laser measurement before adjustment to confirm the 3 mm drift is reproducible and not a setup artifact.