Evaluating the impact of cone-beam computed tomography scatter mitigation strategies on radiotherapy dose calculation accuracy

Abstract

Background and purpose: The scatter induced image quality degradation of cone-beam computed tomography (CBCT) prevents more advanced applications in radiotherapy. We evaluated the dose calculation accuracy on CBCT of various disease sites using different scatter mitigation strategies. Materials and methods: CBCT scans of two patient cohorts (C1, C2) were reconstructed using a uniform (USC) and an iterative scatter correction (ISC) method, combined with an anti-scatter grid (ASG). Head and neck (H&N), lung, pelvic region, and prostate patients were included. To achieve a high accuracy Hounsfield unit and physical density calibrations were performed. The dose distributions of the original treatment plans were analyzed with the γ evaluation method using criteria of 1%/2 mm using the planning CT as the reference. The investigated parameters were the mean γ (γ mean ), the points in agreement (P γ≤1 ) and the 99th percentile (γ 1% ). Results: Significant differences between USC and ISC in C1 were found for the lung and prostate, where the latter using the ISC produced the best results with medians of 0.38, 98%, and 1.1 for γ mean , P γ≤1 and γ 1% , respectively. For C2 the ISC with ASG showed an improvement for all imaging sites. The lung demonstrated the largest relative increase in accuracy with improvements between 48% and 54% for the medians of γ mean , P γ≤1 and γ 1% . Conclusions: The introduced method demonstrated high dosimetric accuracy for H&N, prostate and pelvic region if an ASG is applied. A significantly lower accuracy was seen for lung. The ISC yielded a higher robustness against scatter variations than the USC.

Comparison of CBCT‐based dose calculation methods in head and neck cancer radiotherapy: from Hounsfield unit to density calibration curve to deep learning

“…This simple method appeared to be insufficient owing to artifacts and patient scattering. 50,51 Using this method, the main dose discrepancies were obtained at the shoulder level (Fig. S3), where scatter artifacts are more present.…”

Evaluation of a cycle-generative adversarial network-based cone-beam CT to synthetic CT conversion algorithm for adaptive radiation therapy

“…A CBCT possesses image artifacts due to detector scatter, patient specific scatter, image lag and beam hardening, making dose calculations prone to errors. Many calibration approaches for accurate dose calculations on CBCT currently exist [10]: Patient-or population-specific CT number to electron density calibration (CT-ED-calibration) [11], bulk density override [12], image processing algorithms that further improve the image quality [13][14][15] or deformable image registration (DIR) [7,8] between the CBCT and the treatment planning CT (pCT) to create a deformed CT or a deformed dose in order to assess anatomical and dosimetric changes [16,17]. Recently, deep learning (DL) approaches gained popularity since they can be custom tailored to individual treatment components like image processing and can substantially accelerate time-consuming workflow steps in ART [18,19].…”

Technical Note: Long‐term stability of Hounsfield unit calibration for cone beam computed tomography

“…One limitation of our study was that only CBCT systems with ASG were investigated but no ASG influence on calibration stability is expected, even if the ASG improves HU and dose calculation accuracy . Furthermore, CBCT systems from only one vendor were investigated and the dosimetric evaluation was limited to water.…”

“…Improvements in image quality may facilitate the expansion of its field of use in adaptive radiotherapy . Various adaptive strategies involve dose calculations, which requires an accurate Hounsfield unit (HU) calibration. Different characteristics of linac integrated CBCT scanner such as image lag, panel sensitivity, bad pixels, source output may vary over time and may impact the (CB)CT number but its temporal stability has not been investigated extensively.…”