Room: Exhibit Hall | Forum 2
Purpose: The aim of this study is to verify the transmission factor of commercial transmission detector in clinical use.
Methods: Dolphin detector were used as transmission detector. The transmission factors of Dolphin detector were evaluated for 6 MV, 6 flattening filter free (FFF), 10 MV, and 10 FFF generated by TrueBeam STx linear accelerators. The two dimension dose distributions were acquired for 10 IMRT and 10 VMAT clinical plans by Portal Dosimetry with and without Dolphin. The transmission factors were derived using non-negative least squares problem solver and the 2D dose matrix. New plans were generated by normalizing original plans with transmission factors. Gamma test were performed using ArcCheck detector and portal dosimetry with new plans. The criteria was set to 2 % / 2 mm and 1% / 1 mm.
Results: The transmission factors were determined as 0.878, 0.824, 0.913 and 0.883 for 6 MV, 6 FFF, 10 MV and 10 FFF, respectively. The average dose difference between the original plan without Dolphin and normalized plan with Dolphin was less than 2.0% for all plans. The maximum dose difference of those was up to 10% in high dose gradient region. For portal dosimetry with normalized plan and Dolphin detector, the passing rates of gamma evaluation were 97.2% and 79.1% with 2 % / 2 mm and 1% /1 mm criteria, respectively. Using ArcCheck, those were 96.9% and 75.8% with 2 % / 2 mm and 1% /1 mm criteria, respectively.
Conclusion: Dolphin detector can be for online dosimetry when valid transmission factor applied and verified.