Topical contrast agents to improve soft-tissue contrast in the upper airway using cone beam CT: a pilot study

AbstractThe sharp dose gradients in intensity-modulated radiation therapy increase the treatment sensitivity to various inter- and intra-fractional uncertainties, in which a slight anatomical change may greatly alter the actual dose delivered. Image-guided radiotherapy refers to the use of advanced imaging techniques to precisely track and correct these patient-specific variations in routine treatment. It can also monitor organ changes during a radiotherapy course. Currently, image-guided radiotherapy using computed tomography has gained much popularity in radiotherapy verification as it provides volumetric images with soft-tissue contrast for on-line tracking of tumour. This article reviews four types of computed tomography-based image guidance systems and their working principles. The system characteristics and clinical applications of the helical, megavoltage, computed tomography, and kilovoltage, cone-beam, computed tomography systems are discussed, given that they are currently the most commonly used systems for radiotherapy verification. This article also focuses on the recent techniques of soft-tissue contrast enhancement, digital tomosynthesis, four-dimensional fluoroscopic image guidance, and kilovoltage/megavoltage, in-line cone-beam imaging. These evolving systems are expected to take over the conventional two-dimensional verification system in the near future and provide the basis for implementing adaptive radiotherapy.

Download Full-text

A comparison of kilovoltage and megavoltage cone beam CT in radiotherapy

Journal of Radiotherapy in Practice ◽

10.1017/s1460396907006115 ◽

2007 ◽

Vol 6 (03) ◽

pp. 173-178 ◽

Cited By ~ 10

Author(s):

M. Broderick ◽

G. Menezes ◽

M. Leech ◽

M. Coffey ◽

R. Appleyard

Keyword(s):

Computed Tomography ◽

Soft Tissue ◽

Cone Beam Ct ◽

Cone Beam ◽

Hounsfield Units ◽

Adaptive Planning ◽

Tissue Contrast ◽

Cross Calibration ◽

Conventional Ct ◽

Megavoltage Cone Beam Ct

AbstractAs more and more patients are planned in 3D, the need to verify their position and treatment in 3D also becomes apparent. Megavoltage (MV) and kilovoltage (KV) cone beam computed tomography (CBCT) provide 3D verification of patient position. However, the soft tissue contrast and thus the accuracy of delineation is superior with KV CT imaging. CBCT in conjunction with energy fluence maps from electronic portal imaging devices (EPIDs) could theoretically be used to verify the dose delivered. In this instance, a cross calibration between the KV CBCT and the EPID would be required which would not be necessary with MV CBCT. Adaptive planning with CBCT poses similar challenges for both KV and MV CBCT. Although KV CBCT can produce images with Hounsfield units (HUs) comparable with conventional CT in homogenous phantoms there are large discrepancies in inhomogeneous mediums. If the cupping artefact is corrected for in MV CBCT, the HU values can compare well with KV CBCT for homogenous media. However, advances need to be made to achieve a lower patient dose with MV CBCT. At present, the lower dose required for KV CBCT allows for more frequent imaging and better image quality.

Download Full-text