Abstract
A direct visualization technique for verifying intrafractional localization accuracy of multiple brain metastases during single-isocentre volumetric-modulated arc therapy has been proposed using contrast media-assisted in-treatment cone beam CT (CBCT). Contrast-enhanced planning CT images were acquired immediately after intravenous bolus administration of iodized contrast media at a dose of 2 ml kg–1. Out of 41 nodules detected on the images, 8 lesions were contoured as high-risk gross tumour volumes (GTVs). Prior to each treatment, CBCT imaging was performed to match the skull structures with the planning CT images. Immediately after another intravenous bolus injection of the iodized contrast media at the same dose as administered for the planning CT imaging, contrast-enhanced CBCT images were acquired during volumetric-modulated arc therapy delivery, thereby providing direct verification of time-averaged tumour position during treatment. The planning target volume contours were overlaid with the in-treatment CBCT images, thereby allowing us to directly visualize the localization accuracy of each GTV when the beam delivery was completed. It was visually confirmed that each GTV was accurately localized inside each planning target volume during beam delivery.
Highlights
Contrast-enhanced CT scan has a long history of being used for visualizing brain lesions.[1]
It was later applied to on-board cone-beam CT (CBCT) equipped with a linear accelerator for localizing brain tumours prior to stereotactic treatment in 2008.2,3 The contrast-enhanced CBCT imaging prior to treatment facilitated visual confirmation of the localization accuracy because brain tumours were invisible without administration of the contrast media
When the single-isocentre volumetric-modulated arc therapy (VMAT) is employed for the multiple brain tumours,[7] localization accuracy of the tumours located distant from the isocentre may be of greater concern owing to rotational positioning errors.[8,9]
Summary
Contrast-enhanced CT scan has a long history of being used for visualizing brain lesions.[1] It was later applied to on-board cone-beam CT (CBCT) equipped with a linear accelerator for localizing brain tumours prior to stereotactic treatment in 2008.2,3 The contrast-enhanced CBCT imaging prior to treatment facilitated visual confirmation of the localization accuracy because brain tumours were invisible without administration of the contrast media. The localization accuracy may be decreased during treatment. When the single-isocentre VMAT is employed for the multiple brain tumours,[7] localization accuracy of the tumours located distant from the isocentre may be of greater concern owing to rotational positioning errors.[8,9]
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