Room: AAPM ePoster Library
Purpose: To investigate the optimal combination of volume and reconstruction kV CBCT presets for soft tissue contrast and visualization of the abdominal organs to allow for dose escalation techniques.
Methods: Using the onboard XVI system on an Elekta Versa HD, image quality metric low contrast visibility % was analyzed for different combinations of volume and reconstruction CBCT presets used on the Catphan CTP 503 phantom. Higher low contrast visibility % corresponds to higher noise. Custom volume and reconstruction presets were used to compare the resulting images from varying mA, collimator, filter, slice averaging, and interpolation.
Results: Increasing slice averaging from three to nine resulted in reduced low contrast visibility %. Decreasing mA with constant mS and collimator/filter resulted in decreasing low contrast visibility %. Decreasing the collimator size and not using a bowtie filter in the volume presets also resulted in decreasing low contrast visibility %. Comparisons between reconstruction presets showed that in every case the highest low contrast visibility % was observed with the Bilinear interpolation, while the lowest was when reconstruction used the Partial2 interpolation.
Conclusion: Using trends inferred from the study data, the recommended optimal combination should utilize a low mA, smallest collimator size, no use of a bowtie filter, high slice averaging, and Partial2 interpolation. Caution should be exercised with parameter changes that deviate significantly from clinical presets, especially mA when applied to a patient as opposed to this proof-of-concept phantom study.
Low Contrast Detectability, Image-guided Therapy, SNR