Surface radiation dose comparison of a dedicated extremity cone beam computed tomography (CBCT) device and a multidetector computed tomography (MDCT) machine in pediatric ankle and wrist phantoms

<div><p>Objectives</p><p>To evaluate and compare surface doses of a cone beam computed tomography (CBCT) and a multidetector computed tomography (MDCT) device in pediatric ankle and wrist phantoms.</p><p>Methods</p><p>Thermoluminescent dosimeters (TLD) were used to measure and compare surface doses between CBCT and MDCT in a left ankle and a right wrist pediatric phantom. In both modalities adapted pediatric dose protocols were utilized to achieve realistic imaging conditions. All measurements were repeated three times to prove test-retest reliability. Additionally, objective and subjective image quality parameters were assessed.</p><p>Results</p><p>Average surface doses were 3.8 ±2.1 mGy for the ankle, and 2.2 ±1.3 mGy for the wrist in CBCT. The corresponding surface doses in optimized MDCT were 4.5 ±1.3 mGy for the ankle, and 3.4 ±0.7 mGy for the wrist. Overall, mean surface dose was significantly lower in CBCT (3.0 ±1.9 mGy vs. 3.9 ±1.2 mGy, p<0.001). Subjectively rated general image quality was not significantly different between the study protocols (p = 0.421), whereas objectively measured image quality parameters were in favor of CBCT (p<0.001).</p><p>Conclusions</p><p>Adapted extremity CBCT imaging protocols have the potential to fall below optimized pediatric ankle and wrist MDCT doses at comparable image qualities. These possible dose savings warrant further development and research in pediatric extremity CBCT applications.</p></div

Box plots displaying surface doses in mGy for both examined devices.

<p>a) ankle and wrist, and b) for the different exposure settings “low”, “medium”, and “high”. c) Mean surface doses at different positions around the joints in CBCT and MDCT.</p

Measured surface doses at the six positions around the ankle and wrist.

<p>Measured surface doses at the six positions around the ankle and wrist.</p

Independent samples t-test results between CBCT and MDCT (routine).

<p>Independent samples t-test results between CBCT and MDCT (routine).</p

Exposure parameters for CBCT and MDCT protocols and phantoms.

<p>Exposure parameters for CBCT and MDCT protocols and phantoms.</p

A Bland-Altman plot shows test-retest reliability of all TLD surface dose measurements among each other.

<p>Mean 0.003 (SD ±0.66) mGy shown as solid horizontal line, and upper and lower 1.96 SD intervals presented as dotted horizontal lines at 1.288 and -1.282 mGy respectively. All valid measurements from all six TLD positions were included in the plot.</p

Objective image quality assessment.

<p>CNR, SNR and noise in a) ankle and b) wrist phantom across all exposure settings.</p

Images of measurement setup.

<p>a) CBCT (front) and MDCT (background) scanners used for dosimetry, b) pediatric ankle phantom in the CBCT gantry, c) pediatric wrist phantom in the CBCT gantry.</p

Examples of images quality at different dose levels and image artifacts.

<p>a) Side-by-side comparison of matching slices in CBCT (left) and MDCT (right) ankle examinations rated with good image quality. b) Wrist phantom scanned in CBCT (left) and MDCT (right) rated poor image quality. c) Beam hardening artifacts in CBCT. d) Aliasing artifacts and image noise in MDCT.</p

Positioning of TLDs around the ankle and wrist.

<p>Dosimeter pairs were attached to the phantoms in clockwise position at 1, 3, 5, 7, 9, and 11 o’clock as displayed. a) ankle phantom. b) wrist phantom.</p