Evidence‐based region of interest (ROI) definition for surface‐guided radiotherapy (SGRT) of abdominal cancers using deep‐inspiration breath‐hold (DIBH)

Abstract

To define and evaluate the appropriate abdominal region of interest (ROI) as a surrogate of diaphragm positioning in deep‐inspiration breath‐hold (DIBH) for surface‐guided radiotherapy (SGRT) of abdominal cancers using 3D optical surface imaging (OSI). Six potential abdominal ROIs were evaluated to calculate their correlations with the diaphragm position using 4DCT images of 20 abdominal patients. Twelve points of interest (POIs) were defined (six on the central soft tissue and six on the bilateral ribs) at three superior–inferior levels, and different sub‐groups represented different ROIs. ROI‐1 was the largest, containing all 12 POIs from the xiphoid to the umbilicus and between the lateral body midlines while ROI‐2 had only eight inferior POIs, ROI‐3 had six lateral POIs, and ROI‐4 had four superior‐lateral POIs over the ribs, ROI‐5 contained six central and two most inferior‐lateral POIs and ROI‐6 contained six central and four inferior‐lateral POIs. Internally, the right diaphragm dome was used to represent its positions in 4DCT (0% and 50% within the cycle). The Pearson correlation coefficients were calculated between the diaphragm dome and all 12 external POIs individually or grouped as six ROIs. The quality of the abdominal ROIs was evaluated as potential internal surrogates and, therefore, potential ROIs for SGRT DIBH setup. The four most inferior POIs show the highest mean correlation (r = 0.75) with diaphragmatic motion, and the correlation decreases as POIs move superiorly. The mean correlations are the highest for ROIs with little or no rib support: r = 0.67 for ROI‐2, r = 0.64 for ROI‐5, and r = 0.63 for ROI‐6, while lower for ROIs with rib support: ROI‐1 has r = 0.60, ROI‐3 has r = 0.50, and ROI‐4 has only r = 0.28. This study demonstrates that the rectangular/triangular soft‐tissue ROI (with little rib support) is an optimal surrogate for body positioning and diaphragmatic motion, even when treating tumors under the rib cage. This evidence‐based ROI definition should be utilized when treating abdominal cancers with free‐breathing (FB) and/or DIBH setup.

Feasibility assessment of real-time surface-guided intrafraction radiotherapy for prostate cancer without immobilization

“…The ROI of the optical detection system on the body surface is usually concentrated in a small area, limiting its ability to detect real-time position error outside the ROI. Songy recommends a basis for ROI selection when using OSMS on the abdomen [41]. The selection of ROI for reference images impacts the correlation between body surface optical guidance technology and X-ray image guidance [42].The results of this study con rm that intrafraction position motion error is normally distributed and has a strong correlation.…”

A Potential Pitfall and Clinical Solutions in Surface-Guided Deep Inspiration Breath Hold Radiation Therapy for Left-Sided Breast Cancer

“…First, within the SGRT approach, the ROI should be altered to cover the central part of the abdominal surface, which is correlated (r > 0.6) with the diaphragm motion. 22 The soft abdominal surface is not supported by the rib cage, which is moving with the chest. To ensure significant motion detection in SGRT for abdominal-driven breathing patients, a second ROI could be created on the central abdominal surface to sense the abdominal surface motion, distinguishing A-DIBH from FB, whereas the default chest-only ROI can still be used for FB setup ( Fig.…”

Advances and potential of optical surface imaging in radiotherapy

“…After the SGRT DIBH setup, the IGRT DIBH setup using CBCT yields significantly higher mean shifts in the liver (9 mm) than in the lung (5 mm). To monitor the abdominal motion, it is recommended to exclude the rib cage from the ROI (figure 3(C)) as the lower rib cage moves with the upper one, namely the thorax (Hughes et al 2009, Li et al 2015b, Li et al 2016b, Song et al 2022. The area of the abdominal surface with or without the support or restriction from the rib cage moves differently (further discussion in the clinical research section).…”