Optimizing the TLD-100 readout system for various radiotherapy beam doses using the Taguchi methodology

The TLD-100 readout system was optimized for various radiotherapy beam doses using the Taguchi method. The radiotherapy beam was produced by a Varian 21EX linear accelerator (LINAC) at 6 MV. The beam doses were 50, 100 and 150 cGy, and the measured data in each group were averaged from three TLD-100 chips. A total of nine combinations of four parameters were arranged, in the manner suggested by Taguchi. The four parameters were defined as initial temperature, heating rate, preheat time and maximum set temperature of the readout system during TLD reading. The loss function η adopted herein was specifically defined to satisfy the requirements of both sharp linearity and good reproducibility of the TLD reading at various radiotherapy beam doses. The optimized values were: (1) 50∘C for initial temperature, (2) 3∘C/s for heating rate, (3) 5 min for the TLD preheat time and (4) 250∘C for the maximum temperature for TLD reading. Additionally, the parameters that dominated the TLD readout were: (1) initial temperature, (2) heating rate and (4) maximum temperature setting for TLD reading; and the minor parameter was (3) TLD preheat time before reading. The interactions among the dominant parameters were also studied: no significant cross interaction occurred between initial temperature and heating rate or between initial temperature and maximum temperature. However, a complex cross-interaction existed between optimal heating rate and maximum temperature.