R Nosrati, M Callahan, S Voss, D Zhang*, Boston Children's Hospital, Harvard Medical School

• 
  D Zhang

TU-D1000-IePD-F8-6 (Tuesday, 7/12/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 8

Purpose: ACR/SPR Practice Guidelines recommend urine/serum pregnancy screening for all post-menarcheal females (≥11YO) undergoing CT examinations. The goal of this study is to estimate patient-specific fetus dose to a potentially pregnant pediatric patient from a low dose hip/pelvis CT (LDCT) and determine whether pelvic LDCT examinations can be safely performed with verbal pregnancy screening.

Methods: A retrospective study was performed on 160 female pediatric patients (unknown pregnancy status) between 11-22YO (17.5±3.6YO) who underwent hip/pelvis LDCT (Siemens Somatom-Force). LDCT exams were performed using a weight-adjusted kVp (CarekV) and tube current modulation (CareDose4D). Patient-specific dose from the LDCT was calculated using the National Cancer Institute Dosimetry System for CT (NCICT) database. In brief, each patient was matched to a phantom from the NCI non-reference phantom library (360 size-dependent phantoms) based on patient sex, weight, and height. Patient-specific organ doses were estimated using pre-calculated Monte Carlo simulation results for the selected phantom and CT parameters. Uterus dose was used as a surrogate for fetus dose. Effective dose (ED) was calculated by applying tissue weighting factors. The estimated patient-specific ED were compared to the Dose-Length-Product (DLP) -based ED using age-specific k-factors.

Results: The average patient-specific ED for hip/pelvis LDCT was 0.48±0.19mSv (range: 0.15-1.22mSv) whereas the average DLP-based ED was 1.57±0.76mSv (range: 0.40-4.69mSv). The average uterus dose was 1.52±0.61mSv (range: 0.42-4.81mSv). Both ED and uterus dose were poorly correlated with patient age, weight, and height but highly correlated with CTDIvol (average: 1.83±0.85; range:0.52-5.83mGy). Patient-specific ED and uterus dose by average were 28.43±7.74% and 88.64±19.64% of the numerical value of CTDIvol respectively.

Conclusion: The estimated fetus dose in case of pregnancy was significantly lower than ACR recommended dose limit of 20 mSv suggesting that hip/pelvis LDCT can be safely performed in adolescent and young adult female patients following verification of pregnancy status by verbal attestation only.

Keywords

Not Applicable / None Entered.

Taxonomy

IM- CT: Radiation dosimetry & risk

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