Value of the Acuros reconstruction CBCT algorithm for conventional (non-HyperSight) Ethos systems

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Reconstruction

Background:

• Online adaptive radiotherapy utilizes cone-beam CT (CBCT) to adjust treatment based on daily anatomical changes.
• Varian's Ethos system enables CBCT-based adaptive radiotherapy, but pelvic CBCTs suffer from low contrast.
• Non-HyperSight Ethos Systems (NHES) require optimized image reconstruction for adaptive treatments.

Purpose of the Study:

• To evaluate the added value of the Acuros algorithm for reconstructing pelvic CBCT images on NHES.
• To compare Acuros reconstruction against standard iCBCT reconstruction for phantom and clinical data.
• To assess image quality metrics and observer preference for Acuros-reconstructed CBCTs.

Main Methods:

• Anthropomorphic pelvis phantom CBCTs were acquired bi-weekly, with CT contours propagated.
• Image quality metrics including Signal-to-Noise Ratio (SNR), Contrast-to-Noise Ratio (CNR), uniformity, and resolution were calculated.
• Clinical CBCTs from five prostate cancer patients undergoing adaptive radiotherapy were analyzed, with Acuros reconstruction applied to the pre-treatment CBCTs. Observer scoring was also performed.

Main Results:

• Acuros reconstruction demonstrated superior contrast-to-noise, signal-to-noise, and uniformity compared to iCBCT in phantom studies.
• For clinical CBCTs, Acuros yielded improvements in contrast-to-noise, uniformity, and resolution.
• Observers rated Acuros images as better or similar to iCBCT in 85-95% of cases for the adaptive task.

Conclusions:

• The Acuros algorithm generally outperforms standard reconstruction for pelvic CBCTs on NHES, particularly in phantom studies.
• Clinical evaluation and observer preference indicate that Acuros provides superior or comparable image quality for adaptive radiotherapy.
• The use of Acuros reconstruction is recommended for NHES to enhance adaptive pelvic radiotherapy accuracy.