Purpose: To estimate patient-specific organ dose in children undergoing ¹⁸FDG-PET/CT scans and evaluate the correlation between CT size specific dose estimate (SSDE) and effective dose.
Methods: Organ and whole body doses were calculated on 181 scans in 100 pediatric patients (females/males: 47/53; 11.4±5.2 YO) who underwent ¹⁸FDG-PET/CT scans on a Siemens mCT Biograph-64 scanner. PET/CT scans consisted of 75 diagnostic (Dx) partial body CT, 36 whole body (WB) low-dose attenuation correction (AC) CT, and 74 partial body AC-CT. The CT scan parameters were similar between Dx and AC scans except for Quality Reference mAs (QRM) which was 150 for Dx-CT and 20/35 for AC-CT. Tube current modulation (TCM) was applied to the CT acquisitions and modeled in the dose estimation. The UF/NCI phantom library was used to calculated CT and PET patient-specific organ dose. The FDG administered activity was based on the North American Consensus Guidelines. In addition, CT SSDE values were calculated based on the AAPM TG-220 formulation and the correlation between CT effective dose and SSDE was investigated.
Results: The average PET effective dose was 7.63±2.06mSv. The mean WB-AC, WB-Dx-CT effective doses were 1.50±0.70mSv and 5.97±1.71mSv respectively. The mean total PET+CT effective dose for WB-AC-CT and WB-Dx-CT exams were 6.56±1.06mSv (range: 4.33-9.13mSv) and 11.11±2.29mSv (range: 7.61-16.78mSv) respectively. The four organs which received the highest PET dose were: bladder, heart, brain and liver; and, for the highest WB-AC-CTs, gonads, heart, bladder and small intestine. The estimated CT effective doses showed high correlation with SSDE (R²=0.9) for all examination types (excluding neck); the correlation increased with the CT scan length, demonstrating almost perfect correlation for WB-AC scans (R²=0.99).
Conclusion: This work provides a reference library of organ dose for a wide range of age/weight of pediatric ¹⁸FDG-PET/CT patients. Also, a linear relationship between CT effective dose and SSDE was determined.