Radiation dose during CT scan with PET/CT clinical protocols

The purpose of this study was to evaluate the radiation doses during CT scans by changing tube voltage and tube current, and to estimate the radiation dose for our clinical protocols during transmission measurement in PET/CT scans. Radiation doses were evaluated for Philips GEMINI 16 slices PET/CT and GE DSTe 8 slices PET/CT systems. A CTDI was measured with standard head and body CT dosimetry phantoms in a variety of CT tube voltage and tube current. A pencil ionization chamber with an active length of 100 mm, and electrometer were used for the CTDI measurement. The measurement is carried out at the free-in-air, center and periphery. The average dose was calculated by the weighted CTDI (CTDI_w = 1/3CTDI_100,c + 2/3CTDI_100,p). Specific organ doses were measured with our clinical protocols for transmission measurement with the Philips PET/CT system and GE PET/CT system with TLDs and anthropomorphic phantom. The TLDs used for measurements were selected for an accuracy of plusmn5% and calibrated in an X-ray radiation field. The organ or tissue was selected by the recommendations of ICRP 60. The radiation dose measured by using standard CTDI phantoms during a CT scan is affected by the tube voltage and the tube current. The measured effective doses with transmission measurements for the Philips system were ranged from 0.14 mSv to 55.54 mSv. The measured effective doses with transmission measurements for GE system were ranged from 0.27 mSv to 24.83 mSv. Radiation dose for clinical protocols during transmission measurements in the PET/CT system can be measured using CTDI phantom with ionization chamber and anthropomorphic phantom with TLDs. Further studies need to be performed to find optimal CT acquisition protocols for reducing the patient exposure with same image quality.