Monte Carlo simulation of eye lens dose reduction from CT scan using organ based tube current modulation

Purpose: To investigate lens dose reduction with organ based tube current modulation (TCM) using the Monte Carlo method. Methods: To calculate lens dose with organ based TCM, 36 pairs of X-ray sources with bowtie filters were placed around the patient head using a projection angle interval of 10 degrees for one rotation of Computed Tomography (CT). Each projection was simulated respectively. Both voxelized and stylized eye models and Chinese reference male phantoms were used in the simulation, and tube voltages 80, 100, 120 and 140 kVp were used. Results: Dose differences between two eye models were less than 20%, but large variations were observed among dose results from different projections of all tube voltages investigated. Dose results from 0 degrees (AP) directions were 60 times greater than those from 180 degrees (PA) directions, which enables organ based TCM reduce lens doses by more than 47%. Conclusions: Organ based TCM may be used to reduce lens doses. Stylized eye models are more anatomically realistic compared with voxelized eye models and are more reliable for dose evaluation.