{'fraction_non_alphanumeric': 0.039777983348751156, 'fraction_numerical': 0.014338575393154487, 'mean_word_length': 4.9423076923076925, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Technical Note: Advancing size-specific dose estimates in CT examinations: dose estimates at longitudinal positions of scans.

PURPOSE
AAPM (Report 204) introduced the size-specific dose estimate (SSDE) for the average dose to the center of a fixed-mA scan. International standards establish a method that CT manufacturers and radiation dose index monitoring software may use to calculate SSDE(z) at longitudinal positions of scans with fixed mA or tube current modulation, and its scan range average. We sought to test how accurate SSDE(z) is in tracking the average dose to the transverse slab of an axial image slice (Dslice ), evaluated with Monte Carlo calculation, in chest and abdominopelvic examinations.


METHODS
We retrospectively identified 65 consecutive adult patients undergoing whole-body CT for transcatheter aortic valve implantation (TAVI) planning. Examination parameters (kV, mA, CTDIvol ) were extracted from the DICOM headers. Patient water equivalent diameter DW (z) was calculated at each image slice, excluding the patient table. A previously validated Monte Carlo simulation (Geant4) program was used to evaluate Dslice from chest and abdominopelvic examinations. Alternatively, SSDE(z) was calculated at each slice. The results of the two methods were compared with descriptive statistical outcomes (R, version 4.0.2).


RESULTS
In chest and abdominopelvic CT examinations, Dslice largely changed with anatomic location and uniformly fell off towards scan range edges. Scan range averages were consistent within 2.5-3.1% (median) and 6.3-10.4% (maximum) in two examinations. On individual image slices, SSDE(z) could be lower or higher than Dslice , with deviation ranging from -18.3-85% in two edges (2 × 5 cm) of scan range and from -35.2% to 18.7% in the remaining central region of the scan.


CONCLUSION
This study provides critical inputs for quality assurance programs. is useful to track the average dose of all image slices, but further development may be useful for tracking patient dose at the level of individual image slices, especially near a scan range edge. This article is protected by copyright. All rights reserved.