A study on the effect of using a flattening filter in a medical linear accelerator on the dose distribution

Abstract

This study compared the dependence of the tissue maximum ratio (TMR) and the beam profile on the use of a flattening filter when a linear accelerator is used for radiation exposure of a small field size. To examine change according to the field size, we limit the collimator size to 1, 2 and 3 cm. A water phantom and an ion chamber are used to measure each TMR while a diode is used to obtain the beam profile. The TMR is approximately 4% higher at a depth of 10 cm in the normal mode than it is in the stereotactic radiosurgery (SRS) mode and approximately 8% higher at a depth of 20 cm in the normal mode than it is in the SRS mode. According to the measurement results for the beam profile, the dose decreases slightly faster in the SRS mode than in the normal mode. On the other hand, the two modes do not show any significant difference because similar shapes are observed in the two modes. According to the analysis results for the TMR and the beam profile for a small field size, there are almost no differences between the normal mode and the SRS mode. Therefore, the SRS mode can be used to increase the dose rate in radiation treatments that use a small field size and to reduce the time for treatment.