2051 - Development of Surface Deformation Heatmaps as a Clinical Decision Support Tool for Surface-Guided Deep-Inspiration Breath-Hold Treatments

Purpose/Objective(s): The success of surface-guided deep-inspiration breath-hold (SG-DIBH) treatments depends on accurate identification of suitable candidates and optimal region-of-interest (ROI) placement for surface tracking. Suboptimal selection can result in prolonged treatment times, additional imaging dose, and compromised treatment accuracy. This work presents a patient-specific clinical decision support tool designed to facilitate candidate identification and optimize ROI selection for SG-DIBH stereotactic body radiotherapy (SBRT).

Materials/Methods: The surfaces of 14 SBRT patients were analyzed using an in-house tool developed to assess surface deformation between DIBH and free-breathing (FB). Displacement between DIBH and FB (or mid-ventilation) surfaces, derived from planning CTs, was evaluated both visually and quantitatively. Heatmaps provided a detailed spatial representation of surface displacement, highlighting deformation patterns across the anatomy. Areas of higher deformation most sensitive to surface monitoring appear more red, while areas with minimal deformation between FB and DIBH appear more blue. Quantitatively, the maximum global surface displacement was compared with the internal target motion in the superior-inferior (S/I), anterior-posterior (A/P), and left-right (L/R) directions, as measured between FB and DIBH in the treatment planning system.

Results: Surface deformation patterns vary widely across patients in both magnitude and location. Maximum surface displacement ranged from 6 – 40 mm between patients, with some patients exhibiting maximal displacement inferiorly near the umbilicus, and others superiorly around the sternum. This variability emphasizes the need for patient-specific approaches to ROI selection for accurate surface tracking. Heatmaps effectively visualized these deformation patterns, aiding in optimal ROI placement to maximize the sensitivity of SGRT systems. A significant linear correlation was observed between the maximum surface displacement and internal target S/I motion (R² = 0.73, p<0.05). However, several DIBH patients exhibited minimal surface deformation (<10 mm) despite substantial internal target motion (up to 37 mm S/I), suggesting that surface deformation analysis may provide additional insight for individualized DIBH candidate selection.

Conclusion: DIBH surface deformation and its relationship with internal target motion are highly patient-specific, emphasizing the need for individualized candidacy assessment and ROI selection in SG-DIBH. Surface deformation heatmaps may serve as a valuable decision support tool for a more efficient and robust ROI selection process. Future work will increase the patient cohort to further develop the tool and expand functionality to better inform SG-DIBH treatments.