Evaluation of Accuray Tomo Clear-RT Imaging As a Substitute for Philips Big Bore CT Simulator
Abstract
Purpose
To determine image quality performance of Accuray ClearRT as a substitute for Philips Big Bore CT Simulator.
Methods
First, Accuray’s image acquisition parameters were compared with Philips’ reference and user exam cards for typical protocols. Second, differences between published values and physical measurements were examined for Accuray’s CTDIvol,free air and Philips’ CTDIvol. Finally, simulation of hip prosthesis was conducted using a Cheese Phantom with titanium and reference density plugs to represent metal implants and OARs, respectively. To evaluate metal artifacts, Accuray’s and Philips’ scans were imaged with/without titanium plugs, while reconstructing Philips’ scans with/without O-MAR to gauge algorithm’s functionality. HU calibration curves were defined for both Accuray and Philips using Gammex’s RMI 465 phantom. Scans were imported into Eclipse to contour targets/OARs followed by VMAT planning with Eclipse AAA, copying plan to scans, recalculating dose using same MUs, and comparing DVH values.
Results
Accuray offers longer scan length and higher pitch, but Philips has faster gantry period. Accuray’s FOV, kVp, and mAs are protocol specific, whereas Philips allows manual entry. Except for Head protocols, Accuray uses higher mAs, indicating lower image noise. Published CTDIvol are comparable, although Accuray reports lower Head CTDIvol with reduced kVp and mAs. Measured Accuray CTDIvol,free air average 25% higher (tolerance=50%/1cGy), while measured Philips CTDIvol are maximum 4% higher (tolerance=20%). V95% and V100% for GTV and PTV are similar between systems. Mean, max, and D1% doses to targets/OARs are <4% higher for Accuray. Accuray appears less susceptible to metal artifact: 1) PTV min dose reduces 13% for Philips versus 6% for Accuray and 2) PTV V100% reduces by 6% for Philips versus 1% for Accuray.
Conclusion
Accuray ClearRT offers comparable image performance to Philips Big Bore CT Simulator. Notably, both systems deliver imaging dose within specifications and experience similar dose effects from metal artifacts.