What must be checked for in the monitor used in a linac to control treatment duration?

The correct answer involves checking for both end effect and linearity in the monitor used in a linear accelerator (linac) to control treatment duration.

In radiation therapy, ensuring accurate delivery of the prescribed dose is crucial for treatment efficacy and patient safety. The monitor chamber in the linac plays a critical role in measuring the beam output, which directly influences treatment duration.

End effect refers to the potential discrepancies that may arise at the start and end of the radiation beam. This phenomenon can lead to variations in dose delivery if not accounted for properly. Therefore, it is essential to assess this factor to ensure that the entire treatment length maintains the intended dosimetry.

Linearity, on the other hand, involves the relationship between the deliverable beam output and the dose measured. A linear response is important for predictably relating the monitor readings to the actual dose administered, ensuring that doses are delivered consistently during treatment.

Both of these factors must be monitored as they significantly influence the treatment's accuracy and effectiveness. Regular checks and calibrations involving both end effects and linearity help guarantee that the therapy provided aligns accurately with the treatment plan, ensuring optimal outcomes for patients.