Analysis of output factors with various detectors in small-field electron-beam radiotherapy

To identify an appropriate detector for the precise measurement of small-field electron-beam radiotherapy, we categorized cutout lead blocks into three types by size and shape. We measured the cutout factor for each type of cutout block by using various detectors that are commonly used clinically and then calculated the monitor unit value by using the Monte Carlo algorithm. We repeated each experiment more than five times and averaged the data. Comparisons of the monitor unit values from the Monte Carlo algorithm showed that the output factor measured by using the EDGE detector was relatively accurate, with less than 1% deviation. Data for the other detectors indicated deviations of 3 ~ 15%. It is very important to correctly calibrate the output factor for the treatment of keloids using electron beam radiotherapy due to the small and narrow field size. Use of a special detector with good reproducibility and excellent spatial resolution or calculation of the monitor unit value by using the Monte Carlo algorithm is recommended.