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  • 1. Nowik, Patrik
    et al.
    Bujila, Robert
    KTH, School of Engineering Sciences (SCI), Physics.
    Kull, Love
    Andersson, Jonas
    Poludniowski, Gavin
    The dosimetric impact of including the patient table in CT dose estimates2017In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 23, p. N538-N547Article in journal (Refereed)
    Abstract [en]

    he purpose of this study was to evaluate the dosimetric impact of including the patient table in Monte Carlo CT dose estimates for both spiral scans and scan projection radiographs (SPR). CT scan acquisitions were simulated for a Siemens SOMATOM Force scanner (Siemens Healthineers, Forchheim, Germany) with and without a patient table present. An adult male, an adult female and a pediatric female voxelized phantom were simulated. The simulated scans included tube voltages of 80 and 120 kVp. Spiral scans simulated without a patient table resulted in effective doses that were overestimated by approximately 5% compared to the same simulations performed with the patient table present. Doses in selected individual organs (breast, colon, lung, red bone marrow and stomach) were overestimated by up to 8%. Effective doses from SPR acquired with the x-ray tube stationary at 6 o'clock (posterior-anterior) were overestimated by 14-23% when the patient table was not included, with individual organ dose discrepancies (breast, colon, lung red bone marrow and stomach) all exceeding 13%. The reference entrance skin dose to the back were in this situation overestimated by 6-15%. These results highlight the importance of including the patient table in patient dose estimates for such scan situations.

  • 2.
    Persson, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Royal Inst Technol, Dept Phys, SE-10691 Stockholm, Sweden..
    Bujila, Robert
    Karolinska Univ Hosp, Unit Xray Phys, Sect Imaging Phys Solna, Dept Med Phys, SE-17176 Stockholm, Sweden..
    Nowik, Patrik
    Karolinska Univ Hosp, Unit Xray Phys, Sect Imaging Phys Solna, Dept Med Phys, SE-17176 Stockholm, Sweden..
    Andersson, Henrik
    Karolinska Univ Hosp, Unit Xray Phys, Sect Imaging Phys Solna, Dept Med Phys, SE-17176 Stockholm, Sweden..
    Kull, Love
    Sunderby Hosp, Med Radiat Phys, SE-97180 Lulea, Sweden..
    Andersson, Jonas
    Umea Univ, Radiat Phys, Dept Radiat Sci, SE-90185 Umea, Sweden..
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics. Royal Inst Technol, Dept Phys, SE-10691 Stockholm, Sweden..
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Royal Inst Technol, Dept Phys, SE-10691 Stockholm, Sweden..
    Upper limits of the photon fluence rate on CT detectors: Case study on a commercial scanner2016In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 43, no 7, p. 4398-4411Article in journal (Refereed)
    Abstract [en]

    Purpose: The highest photon fluence rate that a computed tomography (CT) detector must be able to measure is an important parameter. The authors calculate the maximum transmitted fluence rate in a commercial CT scanner as a function of patient size for standard head, chest, and abdomen protocols. Methods: The authors scanned an anthropomorphic phantom (Kyoto Kagaku PBU-60) with the reference CT protocols provided by AAPM on a GE LightSpeed VCT scanner and noted the tube current applied with the tube current modulation (TCM) system. By rescaling this tube current using published measurements on the tube current modulation of a GE scanner [N. Keat, "CT scanner automatic exposure control systems," MHRA Evaluation Report 05016, ImPACT, London, UK, 2005], the authors could estimate the tube current that these protocols would have resulted in for other patient sizes. An ECG gated chest protocol was also simulated. Using measured dose rate profiles along the bowtie filters, the authors simulated imaging of anonymized patient images with a range of sizes on a GE VCT scanner and calculated the maximum transmitted fluence rate. In addition, the 99th and the 95th percentiles of the transmitted fluence rate distribution behind the patient are calculated and the effect of omitting projection lines passing just below the skin line is investigated. Results: The highest transmitted fluence rates on the detector for the AAPM reference protocols with centered patients are found for head images and for intermediate-sized chest images, both with a maximum of 3.4 . 10(8) mm(-2) s-1, at 949 mm distance from the source. Miscentering the head by 50 mm downward increases the maximum transmitted fluence rate to 5.7 . 10(8) mm(-2) s(-1). The ECG gated chest protocol gives fluence rates up to 2.3 . 10(8)-3.6 . 10(8) mm(-2) s(-1) depending on miscentering. Conclusions: The fluence rate on a CT detector reaches 3 . 10(8)-6 . 10(8) mm(-2) s(-1) in standard imaging protocols, with the highest rates occurring for ECG gated chest and miscentered head scans. These results will be useful to developers of CT detectors, in particular photon counting detectors. (C) 2016 American Association of Physicists in Medicine.

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