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Technical Note: Long‐term stability of Hounsfield unit calibration for cone beam computed tomography
Author(s) -
Schröder Lukas,
Stankovic Uros,
Sonke JanJakob
Publication year - 2020
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.14015
Subject(s) - hounsfield scale , imaging phantom , cone beam computed tomography , scanner , nuclear medicine , calibration , cone beam ct , computed tomography , image guided radiation therapy , calibration curve , mathematics , medicine , optics , physics , radiology , statistics , detection limit
Purpose The goal of this study was to investigate the stability of a phantom‐based Hounsfield unit (HU) calibration for cone beam CT (CBCT). Methods Three consecutive scans of a large phantom configuration and a small phantom configuration were acquired and reconstructed with a uniform scatter correction method. The CBCT gray values of the phantom inserts were measured and the three values of each insert averaged. The linear calibration curve was determined and its slope and intercept were evaluated. This procedure was performed for three CBCT scanners (Elekta Synergy) over a period of 10 months with 1, 2, or 4 weeks between measurements. A dosimetric estimation of the HU fluctuations was carried out. Results The CBCT HUs were stable over time with only small variations in slope and intercept resulting in HU differences on the water level, that is, intercepts, of less than 7 HU (standard deviation). Therefore, the dosimetric influence of these HU differences was limited. The inter‐scanner disparities (up to ~ 16 HU) were larger than the intra‐scanner ones (up to ~ 7 HU). Conclusions Stable HUs were observed over a period of 10 months. Due to the differences between the CBCT scanners, scanner‐specific calibration curves are necessary.