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A Comparison of Conebeam CT-Derived and 4DCT-Derived Internal Target Volume for Lung Tumors

V Sarkar

V Sarkar*, L Huang, A Paxton, M Szegedi, P Rassiah-Szegedi, H Zhao, Y Huang, V Pigrish, B Salter, University of Utah, Salt Lake City, UT


SU-H3-GePD-J(A)-5 (Sunday, July 30, 2017) 4:00 PM - 4:30 PM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: This work compares 4DCT and kV conebeam CT (CBCT) imaging to determine whether the internal target volume (ITV) is accurately represented by CBCT acquired for lung SBRT patients.

Methods: Daily 4DCT and CBCT datasets were acquired for each fraction for four different lung SBRT patients. A single clinical expert contoured the ITV on all of the 4DCT datasets. For each patient, the first day’s 4DCT-derived ITV was then copied onto the first day’s CBCT. This CBCT and contour were used to create a patient-specific atlas model in the MIM contouring software. This atlas was then used to auto-contour the ITV on subsequent daily CBCTs for that patient. These atlas-generated CBCT-based ITV volumes were compared to the 4DCT-derived ITV contours for the same day.

Results: The atlas-generated CBCT-derived ITV volumes were similar to the 4DCT-derived volumes. Due to resolution differences between CBCT and 4DCT, small volume differences were observed even when the contours were copied between 4DCT and CBCT (i.e. prior to atlas model generation). Even with this small baseline variation included, the range of ITV volume difference was 0.2% - 4.0%. The average absolute volume difference ranged from 0.03 cc to 1.78 cc. These differences would be even smaller after accounting for the baseline variation due to resolution.

Conclusion: For the patients studied here the present study confirmed that a daily, patient-specific ITV is well represented by kV CBCT acquired for IGRT purposes. Data for additional patients, along with phantom data, is being collected and will be presented.

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