Dosimetric Comparison between Monaco TPS and EGSnrc Monte Carlo simulation on Titanium Rod in 12bit and 16bit Image Format

This study purpose is to investigate the effects of using different bit depth DICOM images for the 6 MV photon beam on a titanium rod. An EGSnrc Monte Carlo simulation on the Elekta Synergy LINAC executed as a dosimetry comparison tool for the TPS. CT scanners with 12-bit, 12-bit extended (Siemens Somatom Definition AS) and 16-bit depth (Toshiba Aquilion) parameters were applied to scan a wax phantom with a titanium rod. A direct beam (AP) with a field size of 10 x 10 cm2 was prescribed 200 cGy dose and was planned on the MONACO TPS. The TPS outcome was compared with the validated LINAC EGSnrc calculation. The downstream dose of the titanium rod was analyzed for each bit-depth parameters and the limitations of the existing TPS were examined. CT numbers of the titanium rod vary for each bit-depth parameter, where 3071 +/- 0 HU, 8513 +/- 31 HU, and 10006 +/- 73 HU for 12-bit, 12-bit extended, and 16-bit images, respectively. The 16-bit depth scanner gives the most accurate CT number of the titanium rod with the correct dose calculation while, the Monaco TPS underestimates the real titanium rod dose compared to the EGSnrc calculations by 4.95%.