Mehran Miron Zaini PhD,MS, Presenter: Nothing to Disclose

W Bryan Jackson MS, Abstract Co-Author: Nothing to Disclose

Kellen K Thuo MS, Abstract Co-Author: Nothing to Disclose

Daily cone-beam CT-based 3D dosimetry allows the observation of anatomical and dosimetric changes in the patients undergoing radiation therapy. To derive meaningful anatomical and dosimetric information from the daily changes to the patient, one needs to observe the temporal changes in the three-dimensional cone-beam CT (CBCT) image volumes. Temporally varying 3D CBCT image volumes constitute a four-dimensional dataset. Four-dimensional spatiotemporal image processing techniques are employed for studying the three-dimensional anatomical and dosimetric videos of the radiation therapy patients.

CBCT image volumes of radiation therapy patients are obtained daily. The exit fluence of 3D-conformal, IMRT, and VMAT radiation beams are acquired using an electronic portal imaging device. Back-projected fluence images onto the CBCT image volumes employing inverse convolution produce 3D dosimetric maps of the daily radiation treatments. Organs and volumes of interest (VOI) are contoured on the daily CBCT image volumes. 3D dose values inside the daily normal and disease contours are tracked in time. Spatiotemporal filters and models are used to assist in extracting clinically relevant information. Velocity vector topographs are employed for visualization of the temporal changes in the radiation treatment delivery and outcome. Movies of the dose maps in the VOIs also aid in the clinical decision making process.

Daily changes in the imparted radiation dose and the shape of the VOIs are clearly visible in the four-dimensional dataset of this work. Spatial extent of the dosimetric shift in some anatomical regions was larger than the estimated values by up to 1.5 cm. It was found that intraframe filters are not needed for smoothing the sparsely sampled time dimension.

Temporal changes in the treated areas and their dose values are anticipated. Such expectations arise from the progress of the treatments, daily setup variations, and patient motion. At some points in the course of the treatment of certain anatomical sites, the need for altering the treatment plan could arise. Movies are a better visualization tool than both the velocity maps and the temporally modulated dose-volume histogram plots.

A clinician could employ the results of this work in assessing whether an alteration in the treatment plan during the course of a fractionated radiation therapy is warranted.

Zaini, M, Jackson, W, Thuo, K, Four-dimensional Image Processing of Daily Cone-Beam CT Volumes.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034298.html