How low can you go? A CBCT dose reduction study

Abstract

Purpose Cone beam computed tomography (CBCT) is often used for patient setup based solely on bony anatomy. The goal of this work was to evaluate whether CBCT dose can be lowered to the level of kV image pair doses when used for bony anatomy‐based IGRT without compromising positioning accuracy. Methods An anthropomorphic phantom was CT scanned in the head, head and neck, chest, and pelvis regions and setup on the linear accelerator couch with the isocenter near the planned location. Cone beam computed tomographies were performed with the standard “full dose” protocol supplied by the linac vendor. With sequentially lowering the dose, three‐dimensional (3D) matching was performed for each without shifting the couch. The standard kV image pair protocol for each site was also used to image the phantoms. For all studies, six degrees of freedom was included in the 2D or 3D matching to the extent they could be employed. Imaging doses were determined in air at isocenter following the TG‐61 formalism. Results Cone beam computed tomography dose was reduced by 81–98% of the standard CBCT protocol to nearly that of the standard kV image pair dose for each site. Relative to the standard CBCT shift values, translational shifts were within 0.3 and 1.6 mm for all sites, for the reduced dose CBCT and kV image pair, respectively. Rotational shifts were within 0.2 degree and 0.7 degrees for all sites, for the reduced dose CBCTs and kV image pair, respectively. Conclusion For bony anatomy‐based image guidance, CBCT dose can be reduced to a value similar to that of a kV image pair with similar or better patient positioning accuracy than kV image pair alignment. Where rotations are important to correct, CBCT will be superior to orthogonal kV imaging without significantly increased imaging dose. This is especially important for image guidance for pediatric patient treatments.

TIGRE-VarianCBCT for on-board cone-beam computed tomography, an open-source toolkit for imaging, dosimetry and clinical research

“…Table 1 also indicates a general trend that when acquired projections were halved off, SNR and CNR values in reconstructed images declined by about 1/3, and SSIM values decreased about 10 %. The finding revealed in this patient-based study [24] is consistent with the phantom based study that CBCT dose can be significantly reduced by protocol optimization.…”

Cone‐beam computed tomography use in postgraduate orthodontic programs in North America and Europe

“…Thirteen multiple‐choice questions were included in the survey. The questions were structured with reference to the previous similar survey study 10 with necessary modifications based on the current reports on CBCT usage in the orthodontic field 1,3,4,6–9,11,12,14,15 . The survey was validated through pilot feedback from two orthodontic faculty members.…”

“…This study indicated that, in North America, only 18.2% of programs used CBCT as a diagnostic tool for every patient. In the 10 years since that study was conducted, there has been updated research regarding advances in low‐dose protocols for CBCT usages, such as mAs reduction, use of partial rotations, reduced numbers of projections, and larger voxel size, which were able to decrease the amount of ionizing radiation to orthodontic patients without compromising the diagnostic integrity of the radiographs 11–13 . Thus, an update on the modern perspectives regarding CBCT usage in orthodontics is needed.…”

Region‐of‐interest intra‐arc MV imaging to facilitate sub‐mm positional accuracy with minimal imaging dose during treatment deliveries of small cranial lesions

“…The imaging dose accrued with MV imaging 18 or CBCT 19 has been a concern with image‐guided radiation therapy, in particular with pediatric cases. Several works have explored the use of region‐of‐interest (ROI) CBCT 20 , 21 and MV‐CT 22 and found possible dose reductions of 16%–90% and 15%–75% with ROI‐based CBCT and MV‐CT, respectively, when compared with full‐field imaging.…”