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On-Treatment Volumetric Imaging During Respiratory Gated VMAT

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K Choi

K Choi*, L Xing, R Li, Stanford Univ School of Medicine, Stanford, CA

SU-E-J-4 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:

To obtain on-treatment volumetric patient anatomy during respiratory gated VMAT.

Methods:

On-board imaging device integrated with Linacs offers a viable tool for obtaining patient anatomy during radiation treatment delivery.
In this study, we acquired beam-level kV images during gated VMAT treatments
using a Varian TrueBeam\texttrademark STx Linac.
These kV projection images are triggered by a respiratory gating signal and can be acquired immediately before
treatment MV beam on
at every breathing cycle during delivery.
Because the kV images are acquired with an on-board imaging device
during a rotational arc therapy,
they provide the patient anatomical information from many different angles
or projection views (typically 20-40).
To reconstruct the volumetric image representing patient anatomy during the VMAT treatment,
we used a compressed sensing method with a fast first-order optimization algorithm.
The conventional FDK reconstruction was also used for comparison purposes.
The method was tested on a dynamic anthropomorphic physical phantom as well as a lung patient.

Results:

The reconstructed volumetric images for a dynamic anthropomorphic physical phantom
and a lung patient showed clearly visible soft-tissue target
as well as other anatomical structures,
with the proposed compressed sensing-based image reconstruction method.
Compared with FDK, the compressed sensing method leads to a ~2- and 3-fold increase
in contrast-to-noise ratio around the target area in the phantom and patient case,
respectively.

Conclusion:

The proposed technique provides on-treatment volumetric patient anatomy,
with only a fraction (<10%) of the imaging dose used in conventional CBCT procedures.
This anatomical information may be valuable for geometric verification and treatment guidance,
and useful for verification of treatment dose delivery, accumulation, and adaptation in the future.

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