What parameters must be corrected for in calibration due to their effects on linear accelerator output?

The chosen answer, which identifies temperature, pressure, and humidity as parameters that must be corrected for in calibration, is correct because these environmental factors can significantly affect the output of a linear accelerator.

Temperature can influence the density of air, which in turn affects the ionization of radiation in air. As temperature changes, the kinetic energy of air molecules varies, impacting how radiation is measured.

Pressure also plays a crucial role in the calibration of a linear accelerator. Changes in atmospheric pressure can affect the density of air and the beam's behavior as it travels through different mediums. Higher pressure increases air density, which can lead to increased attenuation of radiation.

Humidity is another critical factor, as the moisture content in the air can affect the ionization process and the measurement of radiation levels. High humidity can result in changes to the way radiation interacts with the surrounding air.

By correcting for temperature, pressure, and humidity during calibration, operators can ensure that the linear accelerator's output is accurate and reliable, leading to more effective treatment planning in radiation oncology.