Author: Savannah Decker, Grace Gwe-Ya Kim, Laura Padilla 👨🔬
Affiliation: UC San Diego, University of California San Diego 🌍
Purpose: The success of surface-guided deep-inspiration breath-hold (SG-DIBH) treatments depends on accurate identification of suitable candidates. Sub-optimal patient selection can result in prolonged treatment times, additional imaging dose, and compromised treatment accuracy. This work presents a tool to facilitate reliable patient identification for SG-DIBH stereotactic body radiotherapy (SBRT) based on surface deformation and target displacement.
Methods: The surfaces of 14 SBRT patients were analyzed using an in-house tool developed to assess surface deformations. Displacement between DIBH and mid-ventilation phase surfaces from planning CTs was evaluated visually and quantitatively. Visually, heat maps provided a detailed spatial representation of surface displacement, highlighting deformation patterns across the anatomy. Quantitative metrics included maximum global displacement (MGD) and average local displacement (ALD) closest to the internal target. Internal target displacement (ITD) was evaluated as the shift between DIBH and mid-ventilation in the S/I, A/P, and L/R directions. Analysis also examined the correlation between ITD and surface deformation.
Results: There exists large variation in both the location and magnitude of MGD across patients. A significant linear correlation was observed between MGD and internal target A/P displacement (R2 = 0.73, p<0.05). However, several DIBH patients exhibited small MGD (<1 cm) despite substantial ITD (up to 3.7cm S/I). MGD correlated more strongly with ITD compared to ALD, suggesting that a tool providing patient-specific ROI selection may be useful to maximize the sensitivity of SGRT systems.
Conclusion: DIBH surface deformation and its correlation with internal target displacement are patient-specific. Thus, ROI selection for surface tracking and overall assessment of DIBH SGRT candidacy should be as well. Deformation heat maps may provide a valuable 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.