Cone-beam CT localization of internal target volumes for stereotactic body radiotherapy of lung lesions.
OBJECTIVE
In this study, we investigate a technique of matching internal target volumes (ITVs) in four-dimensional (4D) simulation computed tomography (CT) to the composite target volume in free-breathing on-board cone-beam (CB) CT. The technique is illustrated by using both phantom and patient cases.


METHODS
A dynamic phantom with a target ball simulating respiratory motion with various amplitude and cycle times was used to verify localization accuracy. The dynamic phantom was scanned using simulation CT with a phase-based retrospective sorting technique. The ITV was then determined based on 10 sets of sorted images. The size and epicenter of the ITV identified from 4D simulation CT images and the composite target volume identified from on-board CBCT images were compared to assess localization accuracy. Similarly, for two clinical cases of patients with lung cancer, ITVs defined from 4D simulation CT images and CBCT images were compared.


RESULTS
For the phantom, localization accuracy between the ITV in 4D simulation CT and the composite target volume in CBCT was within 1 mm, and ITV was within 8.7%. For patient cases, ITVs on simulation CT and CBCT were within 8.0%.


CONCLUSIONS
This study shows that CBCT is a useful tool to localize ITV for targets affected by respiratory motion. Verification of the ITV from 4D simulation CT using on-board free-breathing CBCT is feasible for the target localization of lung tumors.
Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA. zhiheng.wang@duke.edu
Zhiheng
Z
Wang
Q Jackie
QJ
Wu
Lawrence B
LB
Marks
Nicole
N
Larrier
Fang-Fang
FF
Yin
D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D019047:Phantoms, Imaging; D012119:Respiration; D013238:Stereotaxic Techniques / Q000295:instrumentation; D047368:Tumor Burden