Optimizing lens and organ dose evaluation in head CT examinations using Monte Carlo simulation; Influence of gantry tilt and scan range

Katsunuma, Yasushi*; Sato, Kaoru   ; Hasegawa, Takayuki*; Koba, Yusuke*

In recent years, head CT scans have been used to diagnose subarachnoid hemorrhage, brain tumors, and head trauma. However, because the lens located in the head is at increased risk of cataracts due to radiation exposure, reducing radiation dose is a key challenge. Therefore, adjusting the angle of the gantry (the generator and detector of X ray) of the CT scanner has been used as a means of reducing lens dose. However, the specific angle and imaging range have not been defined in the protocol. In this study, we simulated the behavior of X rays emitted during head CT scans using the JF103 phantom and PHITS code developed by the JAEA, and analyzed the dose distribution in body. Our results quantitatively demonstrated that optimizing the gantry angle and imaging range can significantly reduce the lens dose. This finding will be important for revising protocols to optimize lens protection during head CT scans.