4D-CBCT reconstruction using MV portal imaging during volumetric modulated arc therapy

Satoshi Kida, Naoya Saotome, Yoshitaka Masutani, Hideomi Yamashita, Kuni Ohtomo, Keiichi Nakagawa, Akira Sakumi, Akihiro Haga
Radiotherapy and Oncology 2011, 100 (3): 380-5

BACKGROUND: Recording target motion during treatment is important for verifying the irradiated region. Recently, cone-beam computed tomography (CBCT) reconstruction from portal images acquired during volumetric modulated arc therapy (VMAT), known as VMAT-CBCT, has been investigated. In this study, we developed a four-dimensional (4D) version of the VMAT-CBCT.

MATERIALS AND METHODS: The MV portal images were sequentially acquired from an electronic portal imaging device. The flex, background, monitor unit, field size, and multi-leaf collimator masking corrections were considered during image reconstruction. A 4D VMAT-CBCT requires a respiratory signal during image acquisition. An image-based phase recognition (IBPR) method was performed using normalised cross correlation to extract a respiratory signal from the series of portal images.

RESULTS: Our original IBPR method enabled us to reconstruct 4D VMAT-CBCT with no external devices. We confirmed that 4D VMAT-CBCT was feasible for two patients and in good agreement with in-treatment 4D kV-CBCT.

CONCLUSION: The visibility of the anatomy in 4D VMAT-CBCT reconstruction for lung cancer patients has the potential of using 4D VMAT-CBCT as a tool for verifying relative positions of tumour for each respiratory phase.

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