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arXiv · 2502.01509

Proposal and Evaluation of a Practical CBCT Dose Optimization Method

S. Gros·J. Bian·J. Jackson·M. Delafuente·H. Kang·W. Small Jr·M. Mahesh
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Abstract

Objective: To propose a CBCT dose optimization method using readily available measurement equipment in radiation oncology departments. Approach: A 0.6cc air kerma (Kair) calibrated Farmer chamber measured Kair at isocenter for five default CBCT protocols (HEAD, PELVIS, LARGE PELVIS, THORAX, SPOTLIGHT) on a Varian TrueBeam linac. Imaging parameters were modified to reduce cumulative exposure by reducing projections (by 25%, 50%, 75%) in FDK reconstruction, or lowering single frame exposure by 25%, 50%, 70 to 75%. Cone Beam Dose Index (CBDI) and weighted CBDI (CBDI_w) were measured in CTDI phantoms to correlate with Kair. Image quality was assessed quantitatively (HU linearity, uniformity, low-contrast visibility, high-contrast resolution, spatial integrity) using Catphan604, and qualitatively via anthropomorphic phantoms. Results: A linear relationship between Kair, CTDI, and CBDI_w was established. High-contrast resolution and spatial integrity were unaffected by dose reduction (R < 0.5), while low-contrast visibility strongly correlated with exposure (R > 0.75). HU uniformity and linearity remained stable (<40 HU deviation), except for LARGE PELVIS at <50% single-frame exposure. 80 to 50% dose reduction retained clinically acceptable image quality with minimal artifacts or noise. Significance: CBCT protocols on TrueBeam linacs were optimized for dose reduction. The method enables easy implementation by radiotherapy physicists without diagnostic physics equipment or expertise.

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S. Gros, J. Bian, J. Jackson, M. Delafuente, H. Kang, W. Small Jr, M. Mahesh. 2025-02-03. Proposal and Evaluation of a Practical CBCT Dose Optimization Method. https://arxiv.org/abs/2502.01509

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