Novel angular evaluation method for radiation field using Lie derivative

In radiotherapy, quality assurance (QA) for beam delivery from linear accelerator (linac) of treatment machine is a highly crucial factor for accurate radiotherapy because of the fuctuations in the conditions of the machine. The radiation feld is one of the important evaluation items, and this has been well-checked by crossline (right-to-left) and inline (caudal-to-cranial) profles. Diagonal or angular profles of the radiation feld are also an important component of irradiation feld; however, these are frequently omitted or not fully taken into account as it requires inefcient measurements. To detect the angular and radial conditions of the radiation feld, we proposed a novel evaluation method using Lie derivative analysis against radiochromic flm dosimetry in this study. This method directly compared the detected dose distributions with the calculations, obtained the discrepancy of the fow feld from the mathematical characteristic of Lie derivative, resulted in a detection of the radial and angular discrepancies that have not been handled by conventional gamma analysis.