Program Information
Evaluation and Validation of CBCT 3D-Gamma Analysis to QA Patient Setup
C Nelson*, G Fisher , C Pham , K Casey , C Robinson , S Kirsner , UT MD Anderson Cancer Center, Houston, TX
Presentations
SU-I-GPD-J-94 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Daily patient alignment using CBCT is common practice for accurate localization for many treatment sites in radiation therapy. These alignments can be approved by the physician at the treatment console or offline. The alignment of the CBCT with the planning CT currently is a qualitative analysis. We present an evaluation and testing of a tool that performs a quantitative analysis to QA the CBCT alignment.
Methods: Planning CTs were acquired of three sections of an anthropomorphic phantom, the head and neck, the thorax, and the pelvis. The phantoms were then set-up on the treatment machine using alignment marks from the planning CT. CBCTs of each phantom were acquired. Shifts from 1-3cm in all directions were applied and the CBCT repeated. Post-acquisition, the CBCTs were transferred to the computation server (Mobius3D, Mobius Medical Systems). 3D-gamma comparisons were computed and shifts were recorded to compare to the actual known shifts to test the ability of the system to accurately determine the magnitude of the shift. In addition, 125 CBCTs from 17 patients who had clinically received CBCT for daily alignment were analyzed for 3D-gamma comparison and shift optimization.
Results: The system was able to predict the actual shift within 2.3mm (pelvis) and 2.1mm (thoracic) for shifts up to 2cm. For the head and neck phantom shifts were predicted accurately to than 2.1mm for shifts up to 1cm. Shifts of 3cm and larger in any direction (pelvis and thoracic phantom) and 2cm and larger (head and neck phantom) yielded erroneous shift determinations. On average for 125 CBCTs, the magnitude of a better shift, from the original alignment was 2.1mm, with an average 3D-gamma of 90.7%.
Conclusion: The Mobius software platform was able to QA patient setup using CBCT alignment for three phantoms accurately setup within 2cm in all directions of the target.
Contact Email: