Dose reduction in 4D CT imaging: Breathing signal-guided deep learning-driven data acquisition.

Purpose: 4D CT imaging is essential for radiotherapy planning in thoracic tumors. However, current protocols tend to acquire more projection data than is strictly necessary for reconstructing the 4D CT, potentially leading to unnecessary radiation exposure and misalignment with the ALARA (As Low As Reasonably Achievable) principle. We propose a deep learning (DL)-driven approach that uses the patient's breathing signal to guide data acquisition, aiming to acquire only necessary projection data.

Material and methods: This retrospective study analyzed 1,415 breathing signals from 294 patients, with a 75/25 training/validation split at patient level. Based on the signals, a DL model was trained to predict optimal beam-on events for projection data acquisition. Model testing was performed on 104 independent clinical 4D CT scans. The performance of the model was assessed by measuring temporal alignment between predicted and optimal beam-on events. To assess the impact on the reconstructed images, each 4D dataset was reconstructed twice: (1) using all clinically acquired projections (reference) and (2) using only the model-selected projections (dose-reduced). Reference and dose-reduced images were compared using Dice coefficients for organ segmentations, deformable image registration (DIR)-based displacement fields, artifact frequency, and tumor segmentation agreement, the latter evaluated in terms of Hausdorff distance and tumor motion ranges.

Results: The proposed approach reduced beam-on time and imaging dose by a median of 29% (IQR: 24-35%), corresponding to 11.6 mGy dose reduction for a standard 4D CT CTDIvol of 40 mGy. Temporal alignment between predicted and optimal beam-on events showed marginal differences. Similarly, reconstructed dose-reduced images showed only minimal differences to the reference images, demonstrated by high lung and liver segmentation Dice values, small-magnitude (DIR) displacement fields, and unchanged artifact frequency. Minor deviations of tumor segmentation and motion ranges compared to the reference suggest only minimal impact of the proposed approach on treatment planning.

Conclusions: The proposed DL-driven data acquisition approach has the ability to reduce radiation exposure during 4D CT imaging while preserving diagnostic quality, offering a clinically viable, ALARA-adhering solution for 4D CT imaging.