Purpose: Although the use of thyroid shields for patients for head CT examinations is reasonable and even required by German regulations, so far available shields are often not used due to difficult applicability. New shields that are easier to use and therefore may gain wider acceptance and more frequent use are now available. In this work two new patient shields are investigated regarding their dose reduction effectiveness and applicability and compared to a thyroid/sternum shield typically used as a part of personal protective equipment. Materials and Methods: The reduction of organ doses for thyroid, sternum and mamma were measured with thermoluminescence detectors in an anthropomorphic female phantom. Additionally, the influence of the length or position of the overview scan at the beginning of the CT examination was taken into account. Results: Depending on the patient shield, a reduction of the organ doses for thyroid of 5???24?%, for sternum of 25???48?% and for mamma of 25???70?% could be found. A shift of 25?mm in the cranial direction for the overview scan resulted in a reduction of these organ doses of 12???15?%. Conclusion: Patient shields for cranial CT examinations provide a considerable dose reduction. New models are easily applied and no decrease in image quality through reconstruction artifacts could be found. Therefore, it is advised to use shields which are applied upon the patient without the need to be wrapped around the neck and the overview scan should be positioned as close as possible to the examined region. Key Points: ??New shields provide a compromise between usability and radiation protection. ??Patient shields reduce organ doses even when not directly exposed. ??The overview scan contributes considerably to out of field organ doses. ??Shielding factors are greatly influenced by the positioning of the examination field. Citation Format: ??Liebmann M, L?llau T, Kluge A et?al. Patient Radiation Protection Covers for Head CT Scans ? A Clinical Evaluation of Their Effectiveness. Fortschr R?ntgenstr 2014; 186: 1022???1027
New methods of dosimetry in computed tomography (CT) X‐ray fields require the use of high‐resolution detectors instead of pencil‐type ionization chambers typically used for CT dose index (CTDI) measurements. This paper presents a study on the suitability of a wide range of ionization chambers, diodes, and a two‐dimensional detector array, used primarily in radiation therapy, for CT and cone‐beam CT dosimetry. Specifically, the energy dependence of these detectors from 50 kVp up to 125 kVp is reported. All measurements were performed in reference to a calibrated diode for use in this energy region. The radiation quality correction factors provided by the manufacturer were used, depending on the measured half‐value layer (HVL) for the particular X‐ray beam. Our study demonstrated the general usability of thimble ionization chambers. These thimble ionization chambers showed a maximum variation in energy response of 5%. Ionization chambers with even smaller sensitive volume, and which exhibit similar variation in energy dependence, can be used if higher spatial resolution is required. Furthermore, the investigated detectors are better suited for dosimetry at CT and CBCT units than conventional large volume or flat detectors, due to their rotational symmetry. Nevertheless, a flat detector can be used for certain measurement tasks, such as the acquisition of percent depth‐dose curves or beam profiles for nonrotating beams, which are important for beam characterization.PACS numbers: 87.57.uq, 87.56.Da, 87.57.Q‐
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