SU‐E‐T‐524: The Effect of CT Contrast on CyberKnife Treatment Planning

Purpose: To investigate the effect of CT contrast enhancement (CE) on the 3D dose distributions of non‐coplanar small field beams in the CyberKnife (CK) treatment planning system. Methods: Twenty patients treated by pre‐CE CT plans were recruited to this retrospective plan study. Their post‐CE CT plans were based on the pre‐CE CT plan data and calculated using the same MU and beam paths in either Ray‐Tracing or Monte Carlo (MC) algorithms. The differences in doses of the beam path and the reference point and in DVHs of target and OARs between the pre‐CE CT and the post‐CE CT plans were compared. The minimum dose, the maximum dose, the mean dose, and the dose received to 50% of the target and OARs volumes, and the target volume coverage were also compared. Results: The dose differences between the pre‐CE and post‐CE plans in a single beam path were less than 50 cGy in both calculation algorithms. At the center of target volume, it was 1.9% (maximum 6.2%) in Ray‐Tracing and 1.5% (maximum 4.0%) in MC, with respect to the prescription dose. The post‐CE plans showed on average 2% decrease in the OAR maximum dose (maximum 6.4% in Ray‐Tracing and 5.8% in MC). Regardless of the algorithms, the dose to the target and the target volume coverage of post‐CE plans were on average reduced by 2% and 1 %, respectively, with a maximum reduction of 6.1% (in Ray‐Tracing) in the minimum target dose. Conclusions: The CK treatment plan using the post‐CE CT could generally result in a few % dose differences from the pre‐CE CT plan. However, it could be more than 6%, depending on the target positions in the body and the calculation algorithms. Thus the post‐CE CT in CK treatment plans should be used with a caution.