Characterization of an advanced cone beam CT (CBCT) reconstruction algorithm used for dose calculation on Varian Halcyon linear accelerators

Abstract

In this study, the performance of a new iterative reconstruction algorithm, the pre-clinical AcurosXB iCBCT algorithm, has been characterized on Varian Halcyon linear accelerators with respect to the potential of radiotherapy dose calculations on CBCT images. The study utilized various phantom setups to verify the accuracy of the pre-clinical algorithm under different scatter conditions and compared dose calculations performed on CBCT images reconstructed with the pre-clinical algorithm to those performed on typical planning CT images. The results indicated that despite showing improvements compared to the existing iCBCT protocol, certain restrictions should be introduced when the pre-clinical AcurosXB iCBCT algorithm was used for dose calculations. Changes in the scatter condition exhibited a larger effect on CBCTs than on planning CTs. Therefore, users should be careful in offsetting the patient and positioning the patient’s arms if the resultant images will be used for dose calculations. In addition, protocols with different kV settings should be approached with caution, where 100 kV protocols should only be used to scan the head and neck area, while the rest of the body should be scanned with the 125 kV and 140 kV protocols. When the patient is set up properly and the appropriate energy is selected for the anatomical area, the uncertainty of using the novel AcurosXB iCBCT algorithm for treatment planning dose calculation is within ± 2.0%.

Feasibility of bone marrow edema detection using dual‐energy cone‐beam computed tomography

“…The proposed DE CBCT framework relies on algorithmic corrections to mitigate the impact of x-ray scatter and FPD lag and glare. While such corrections are increasingly available on advanced CBCT systems, [56][57][58][59] it is nevertheless important to understand their impact in BME imaging to inform the requirements for clinical translation. Figure 9 shows VNCa maps of Phantom-I scanned at Position 4 using 80 mm collimation; each row presents an image obtained by disabling one correction and executing the remaining processing steps and the span coefficient calibration procedure (Section 2.2.4) using the partly uncorrected input data.…”

Evaluation of a cone-beam computed tomography system calibrated for accurate radiotherapy dose calculation

“…Moreover, since anatomical variations in patients can occur, adaptive strategies are needed to account for discrepancies between planned and delivered dose. Therefore, there has been a growing interest in utilizing CBCT imaging for plan adaptation instead of repeat computed tomography (CT) [5] , [6] , [7] , [8] . However, the lower image quality caused by photon scatter, limited field-of-view (FOV), and inconsistency in CT numbers for conventional CBCT compared to fan-beam CT can lead to lower dose calculation accuracy [2] , [9] , [10] , [11] , [12] , [13] , [14] , [15] .…”

“…Dose calculations in photon therapy are typically based on a CT scan of the patient, with CT numbers converted to mass densities (MD) or relative electron densities (RED) by applying a conversion curve [17] , [18] . This has been adapted to CBCT in multiple studies, but the noise and scatter considerably influence the relationship between the CT numbers and corresponding MD/RED [5] , [9] , [15] , [16] , [19] , [20] , [21] , [22] . A study showed that for thoracic patients, the calibration method and accuracy were dependent on the CBCT system [23] .…”

“…The iCBCT is widely available for C-arm linacs and recently also for ring gantry linacs [35] , [36] , [37] , [38] . The iCBCT has led to improved accuracy in dose calculation, although inconsistencies remain when dealing with different scattering conditions [5] , [19] .…”

2D antiscatter grid and scatter sampling based CBCT method for online dose calculations during CBCT guided radiation therapy of pelvis

“…For example, scatter is one of the major reasons behind raw data contamination in CBCT.Improved scatter correction methods can improve CT number accuracy, and dose can be calculated more accurately by using the CBCT images directly. [28][29][30][31] This approach also simplifies the clinical workflow and reduces potential dosimetric errors associated with density overrides, deformable image registration, and synthetic CT generation. However, one potential drawback of existing methods is the accuracy of the achieved HU values through these physicsdriven approaches.…”