Standardization of scan protocols for RT CT simulator from different vendors using quantitative image quality technique.

Objective: To investigate the feasibility of standardizing RT simulation CT scanner protocols between vendors using target-based image quality (IQ) metrics.

Method And Materials: A systematic assessment process in phantom was developed to standardize clinical scan protocols for scanners from different vendors following these steps: (a) images were acquired by varying CTDI and using an iterative reconstruction (IR) method (IR: iDose and model-based iterative reconstruction [IMR] of CT-Philips Big Bore scanner, SAFIRE of CT-Siemens biograph PETCT scanner), (b) CT exams were classified into body and brain protocols, (c) the rescaled noise power spectrum (NPS) was calculated, (d) quantified the IQ change due to varied CTDI and IR, and (e) matched the IR strength level. IQ metrics included noise and texture from NPS, contrast, and contrast-to-noise ratio (CNR), low contrast detectability (d'). Area under curve (AUC) of the receiver operation characteristic curve of d' was calculated and compared.

Results: The level of change in the IQ ratio was significant (>0.6) when using IMR. The IQ ratio change was relatively low to moderate when using either iDose in CTp (0.1-0.5) or SAFIRE in CT (0.1-0.6). SAFIRE-2 in CT showed a closer match to the reference body protocol when compared to iDose-3 in CT. In the brain protocol, iDose-3 in CT could be matched to the low to moderate level of SAFIRE in CT. The AUC of d' was highest when using IMR in CT with lower CTDI, and SAFIRE in CT performed better than iDose in CT CONCLUSION: It is possible to use target-based IQ metrics to evaluate the performance of the system and operations across various scanners in a phantom. This can serve as an initial reference to convert clinical scanned protocols from one CT simulation scanner to another.