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Assessment of Thyroid Dose From Routine Chest CT Scans

K Brown, S King, M Erdman, R Al-Senan*, Penn State Milton S. Hershey Med Ctr., Hershey, PA


(Sunday, 7/12/2020) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]

Room: Track 1

Purpose: To evaluate the accuracy of dose estimates to the thyroid gland from routine chest CT examinations provided by Monte Carlo based estimates from commercially available dose monitoring software.

Methods: Six calibrated optically stimulated luminescent dosimeters (OSLD’s) were inserted into holes drilled in the sections of a Rando anthropomorphic phantom at the location of the thyroid gland. The AAPM recommended chest CT protocol was used to scan the phantom at two tube voltage settings (120 kV and 100 kV). The phantom was also scanned with reduced pitch at 120 kV. The phantom was scanned fifteen times using each protocol with dosimeters replaced between each scan. Scans were sent to CT dose monitoring software (Radimetrics, Bayer HealthCare LLC) for dose analysis using Monte Carlo software and comparison to measured values.

Results: The coefficient of variation for the 15 measurements using each of the three protocols was 16%, 14%, and 14% respectively for the 120 kV, 100 kV, and lower pitch scans. This variation was likely due to the random beam starting angle and beam location relative to the thyroid gland for each scan. The mean thyroid gland dose was calculated (21 mGy, 19 mGy, and 18 mGy) respectively and compared to the organ dose reported by the dose monitoring software (12 mGy, 9 mGy, and 11 mGy) respectively for each protocol. This represents a 40 to 50% discrepancy in OSLD measurements compared to the reported dose from Monte Carlo simulation software. Potential causes for this variation may be due to phantom selection, beam modeling, and scan range mapping by the software.

Conclusion: Monte Carlo based organ dose estimates from a commercially available dose monitoring program significantly underestimate thyroid gland dose from routine chest CT examinations.


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Not Applicable / None Entered.

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