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A Simple Approach to Account and Report Organ Dose From KV Image Guidance Procedures


A Nelson

A Nelson*, G Ding, Vanderbilt University, Nashville, TN

SU-E-I-11 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
To explore a simple approach to report and account for dose resulting from kV imaging procedures.

Methods:
Patient dose distributions resulting from Varian kV-CBCT scans with different imaging scan protocols were calculated by using Monte-Carlo methods. A total of 29 representative patients were studied including the Standard Head(15), Low-Dose Thorax(9), and Pelvis(5) scan protocols. Dose dependence on isocenter location was explored by simulating the same patient scanned with three different isocenters each 5cm apart in the anterior-posterior direction. Additionally, two pediatric head scans were simulated to demonstrate size dependence for the Standard Head protocol. The patient organ doses were analyzed using in-house software that performs DVH analysis.

Results:
The mean organ dose ranges across patients for Standard Head scans: Eye, Brain, Brainstem, Skin, and Bone: 0.03-0.32cGy, 0.22-0.31cGy, 0.19-0.29cGy, 0.26-0.38cGy, and 0.70-1.02cGy, respectively. The wide range in eye dose was due to isocenter dependence for the posterior 200° Standard Head scan, where the scan angle does not spare eye dose for highly anterior isocenters. For Thorax and Pelvis scans, the dose to soft tissues showed small variation: 0.32-0.61cGy and 1.20-2.20cGy for Thorax and Pelvis, respectively.

Conclusion:
The results show that both soft tissue organ doses and bone dose show small variation between the patients studied. Although a large variation was observed for eye dose from head scans due to the asymmetric scan rotation and isocenter position differences, the doses are much lower and can therefore be reasonably estimated with an upper limit. This study indicates that it may be acceptable to estimate and account for organ dose by using simple tabulated values based on scan procedure without using patient-specific data. While this approach is not as accurate as patient-specific calculations, the simplicity of this method can enable reporting and accounting for imaging dose in patient treatment planning feasible.

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