AbstractID: 9681 Title: Shielding calculations for a hybrid CT-PET scanner
The hybrid CT-PET scanner presents a unique problem for shielding calculations. These must consider higher radiation levels inside
the scanner room and inside the patient waiting room where the patient awaits for the uptake of positron emitting radiopharmaceutical
before the scanning process begins.
Shielding calculations were made for an installation housing a hybrid CT–PET scanner. For each barrier of the installation, the
shielding requirements for the CT and the PET workloads were calculated separately. The shielding calculations for CT-scanner were
based on iso-exposure lines measured by the manufacturer adjusted for the maximum patient workload, distances to the occupied
areas, occupancy factors of the surrounding areas and NCRP dose limits for the occupied areas. For the PET scanner, shielding
calculations were based on the exposure rates measured by the manufacturer for a positron-emitting source.
The control room wall and the viewing window in it were the only barriers in the scanner room, which needed 5 mm lead equivalence
shielding against PET (511 KeV) radiation. The other walls and the entrance door to the room needed 1.5 mm or less shielding for CT
x-rays of 140 kVp. Above the ceiling was an uncontrolled area with full occupancy and the dose limit was set to 0.02 mSv/week. The
ceiling needed additional shielding of 1.5 mm lead for 140 kVp x-rays. A portion of the wall in patient waiting room required 8 mm
lead shielding.
In conclusion, hybrid CT-PET scanners may require varying shielding for each barrier for PET and CT scanning processes.