Local temperature and pressure variations and its effects on daily ionometric measurements of radiation beam outputs from linear accelerators

As part of the quality assurance protocol for linear aceelerators at West Virginia University Hospitals, the local temperature and pressure are recorded on a daily basis by the radiation therapists. These temperature and pressure values are not used for temperature and pressure correction unless the ionometric measurements of radiation beam outputs from linear accelerators are outside the established tolerance levels. This paper presents a study on the variation of temperature and pressure over the past two years. Analysis of the data showed that the variation of pressure is within ± 1.5% of the average value. Likewise, the variation of temperature is within ±1.5% of the average value. The worst possible effects of temperature and pressure on ionometric measurements would be within ±3%, which is at the tolerance levels recommended by the American Association of Physicists in Medicine (AAPM) Task Group No. 13. By maintaining machine output fluctuation to within ±2%, the maximum deviation of uncorrected ionometric measurements would be within ±5%. This study collaborates with the tolerance levels suggested by the AAPM Task Group No. 40.