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Megavoltage computed tomography for tomotherapeutic verification
Author(s) -
Ruchala Kenneth J.
Publication year - 2000
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.598994
Subject(s) - tomotherapy , imaging phantom , linear particle accelerator , iterative reconstruction , nuclear medicine , image guided radiation therapy , image quality , tomography , medical physics , medical imaging , medicine , radiation therapy , computer science , radiology , optics , artificial intelligence , physics , image (mathematics) , beam (structure)
A helical tomotherapy system is being developed at the University of Wisconsin—Madison as a means of improving Intensity Modulated Radiotherapy (IMRT) delivery. The goal of this thesis was to develop megavoltage computed tomography (MVCT) capabilities to image the patient in the treatment position, before, during, or after IMRT treatment. This MVCT system uses a 738‐channel xenon detector and is similar to helical kilovoltage CT (kVCT) except that it utilizes the treatment linac as the x‐ray source. Due to the high (4 MV) photon energy, MVCT contrast is inferior to kVCT, but should be adequate to verify patient positioning for radiotherapy. Techniques were developed to preprocess transmission data and to correct for artifacts. Image quality was compared for several different reconstruction algorithms. MVCT scans on a tomotherapy research system demonstrated relative contrasts below 1% for 25 mm objects using a 7 cGy dose to the center of the phantom. High‐contrast resolutions are 1.25 mm for air cavities. Through calibration of this system with known materials, the reconstructed values have been demonstrated to be linear with electron density, which benefits subsequent dose calculations. MVCT using transmission data collected during IMRT treatment delivery was also investigated. By overcoming the problems of incomplete data availability and difficulty normalizing modulated beams, treatment data was incorporated into the reconstruction process. This has demonstrated improved image contrast while reducing the additional imaging dose, and also presents the opportunity to collect all of the data necessary for image reconstruction during the treatment delivery.