ABSTRACT
PURPOSE: To evaluate digital tomosynthesis (DTS) technology for daily positioning of patients receiving accelerated partial breast irradiation (APBI) and to compare the positioning accuracy of DTS to three-dimensional cone-beam computed tomography (CBCT). METHODS AND MATERIALS: Ten patients who underwent APBI were scanned daily with on-board CBCT. A subset of the CBCT projections was used to reconstruct a stack of DTS image slices. To optimize soft-tissue visibility, the DTS images were reconstructed in oblique directions so that the tumor bed, breast tissue, ribs, and lungs were well separated. Coronal and sagittal DTS images were also reconstructed. Translational shifts of DTS images were obtained on different days from the same patients and were compared with the translational shifts of corresponding CBCT images. Seventy-seven CBCT scans and 291 DTS scans were obtained from nine evaluable patients. RESULTS: Tumor beds were best visible in the oblique DTS scans. One-dimensional positioning differences between DTS and CBCT images were 0.8-1.7 mm for the six patients with clips present and 1.2-2.0 mm for the three patients without clips. Because of the limited DTS scan angle, the DTS registration accuracy along the off-plane direction is lower than the accuracy along the in-plane directions. CONCLUSIONS: For patients receiving APBI, DTS localization offers comparable accuracy to CBCT localization for daily patient positioning while reducing mechanical constraints and imaging dose.
Subject(s)
Breast Neoplasms/diagnostic imaging , Breast Neoplasms/radiotherapy , Cone-Beam Computed Tomography/methods , Imaging, Three-Dimensional/methods , Radiographic Image Enhancement/methods , Equipment Design , Female , Humans , Observer Variation , Radiation Injuries/prevention & control , Radiotherapy DosageABSTRACT
PURPOSE: On-board cone-beam computed tomography (CBCT) provides soft tissue information that may improve setup accuracy in patients undergoing accelerated partial breast irradiation (APBI). We used CBCT to assess the residual error in soft tissue after two-dimensional kV/MV alignment based on bony anatomy. We also assessed the dosimetric impact of this error. METHODS AND MATERIALS: Ten patients undergoing APBI were studied as part of an institutional review board-approved prospective trial. Patients were aligned based on skin/cradle marks plus orthogonal kV/MV images registered based on bony landmarks to digitally reconstructed radiographs from the planning CT. A subsequent CBCT was registered to the planning CT using soft tissue information. This "residual error" and its dosimetric impact was measured. RESULTS: The root-mean-square of the residual error was 3, 4, and 4 mm, in the right-left, anterior-posterior, and superior-inferior directions, respectively. The average vector sum was 6+/-2 mm. Average reductions in mean dose to the lumpectomy cavity, clinical target volume (CTV), and planning target volume were 0.1%, 0.4%, and 1%, respectively. The mean difference in the clinical target and planning target volumes that received 95% of the prescribed dose (V95) were 1% and 4%. CONCLUSIONS: In this initial study with a modest number of patients, the residual error in soft tissue was typically <5 mm, and with the field margins used, the resultant dosimetric consequences were modest. In patients immobilized in a customized cradle, setup using orthogonal kV images thus appears accurate and reproducible. The CBCT technique may have particular utility in patients with larger breast volumes or breast deformations. Further studies involving larger numbers of patients are needed to further assess the utility of CBCT.
