Measuring skin dose in CT examinations under complex geometries: Instruments, methods and considerations.

Area of Science:

• Medical Physics
• Radiological Sciences
• Diagnostic Imaging

Background:

• Accurate estimation of skin dose in Computed Tomography (CT) is crucial for patient safety.
• Scanning geometry significantly influences radiation dose distribution.
• Developing reliable methods for measuring entrance skin dose (ESD) is essential.

Purpose of the Study:

• To investigate skin dose in CT examinations.
• To evaluate the dependence of skin dose on scanning geometry.
• To compare the performance of two instruments for dose measurement.

Main Methods:

• Measurements of entrance surface air kerma (ESAK) and ESD were performed on an anthropomorphic phantom using a 64-slice CT scanner.
• Two instruments, the Dose Profiler (DP) and QED skin diode (QEDSD), were utilized.
• Axial and helical scan modes were employed to assess dose profiles and point doses.

Main Results:

• Both DP and QEDSD showed good agreement for point dose and profile measurements of ESAK.
• ESD measurements also agreed well, except in helical scans due to scan variability.
• Observed that ESD values correlated with ESAK at equivalent off-phantom distances.

Conclusions:

• DP and QEDSD are suitable for point ESD measurements in CT.
• Accurate calculation of comprehensive skin dose distribution in CT is complex.
• A practical approach involves using isocenter ESAK for a conservative peak skin dose estimate.