Comparison of three differently shaped ROIs in free breathing breast radiotherapy setup using surface guidance with AlignRT®

Abstract

Background: Setup accuracy within adjuvant radiotherapy of breast cancer treated in free breathing is well studied, but a comparison of the typical regions of interest (ROI) used in surface guided radiation therapy (SGRT) does not exist.The aim of this study was to estimate the setup accuracy obtained with differently shaped ROIs in SGRT. Materials and methods: A total of 573 orthogonal image pairs were analyzed from free breathing breast patients in two groups: positioning using AlignRT® surface guidance system (Group A, n = 20), and setup using conventional laser and tattoo setup (Group L, n = 20). For SGRT, three different setup ROIs were used: a Breast-shaped, O-shaped and T-shaped (B-O and T-ROI). We evaluated the isocenter-, rotation-, pitch and arm position accuracy and residual errors for the chest wall and shoulder joint in kV orthogonal and tangential setup images with laser-or SGRT-based setup.Results: Less isocenter variance was found in Group A than in Group L. Rotations and posture errors were larger in group L than in Group A (p ≤ 0.05). Rotation error was smaller with T-shaped ROI than with O-or B-shape (p = 0.01-0.05). Conclusion:Setup with AlignRT® improves reproducibility compared to laser setup.Between the different ROI shapes only small differences were found in the patient posture or the isocenter position in the images. The T-ROI is recommended to set up the chest wall bony structure and an additional B-ROI may be used to fine-tune the soft tissue accuracy.

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

“…To best reproduce the breast shape and position, a two‐step breast SGRT setup procedure (to align the arm and chin first) has been studied and clinically implemented to minimize breast deformation 17 . Three different ROI definitions, including B‐ROI (the breast and chest), O‐ROI (the B‐ROI but carving out the central breast area), and inverse T‐ROI (the chest on the sternum and ribs below the breasts), produce similar SGRT breast setup results with only small differences 14 . For the DIBH setup, as the objective is to monitor the chest wall elevation that allows the heart to separate from the chest wall, so the same ROI can be used to monitor the rise of the thorax from FB to DIBH.…”

“…As SGRT is becoming more commonplace for breast patient setup (in both FB and DIBH settings), there is a general consensus on what the ROI should be to reproduce the breast position for radiotherapy treatment. 14 , 17 For FB setup, the ROI typically includes the central chest area on the sternum since this anatomy is the most stable (more consistent with bony movement and less deformable). Although the breast is often deformable (especially for large patients or patients with pendulous breasts), at least some part of the breast should be included in the ROI to localize the breast for accurate setup.…”

“… 17 Three different ROI definitions, including B‐ROI (the breast and chest), O‐ROI (the B‐ROI but carving out the central breast area), and inverse T‐ROI (the chest on the sternum and ribs below the breasts), produce similar SGRT breast setup results with only small differences. 14 For the DIBH setup, as the objective is to monitor the chest wall elevation that allows the heart to separate from the chest wall, so the same ROI can be used to monitor the rise of the thorax from FB to DIBH. Therefore, the ROI definition should be consistent between both FB and DIBH and can be copied from one DICOM surface to the other for preparing SGRT set up in the clinic.…”

“…It is critical to find reliable ROIs on the skin surfaces to serve as a good body surrogate for patient setup. 13 , 14 , 15 …”

Informe del Grupo de Trabajo de la SEFM sobre Radioterapia Guiada por Superficie (SGRT): Procedimientos recomendados para la aceptación y puesta en funcionamiento

“…En aquellos sistemas de SGRT que requieran la delimitación de una región de interés a monitorizar, dependiendo de qué parte de la anatomía incluya, proporcionará distintos valores de desplazamientos. 90 El usuario deberá establecer, para cada patología, la extensión y forma del área a monitorizar que mayor correlación presenta con la posición de la anatomía interna a tratar.…”