Abstract
The purpose of this study was to test the feasibility of using respiratory correlated mega voltage cone‐beam computed tomography (MVCBCT), taken during patient localization, to quantify the size and motion of lung tumors. An imaging phantom was constructed of a basswood frame embedded with six different‐sized spherical pieces of paraffin wax. The Quasar respiratory motion phantom was programmed to move the imaging phantom using typical respiratory motion. The moving imaging phantom was scanned using various MVCBCT imaging parameters, including two beam line types, two protocols with different ranges of rotation and different imaging doses. A static phantom was also imaged as a control. For all the 3D volumetric images, the contours of the six spherical inserts were measured manually. Compared with the nominal sphere diameter, the average relative error in the size of the respiratory correlated MVCBCT spheres ranged from 5.3% to 12.6% for the four largest spheres, ranging in size from 3.6 cc to 29 cc. Larger errors were recorded for the two smallest inserts. The average relative error in motion was 5.1% smaller than the programmed amplitude of 3.0 cm. We are able to conclude that it is feasible to use respiratory correlated MVCBCT to quantify tumor motion for lung cancer patients.PACS numbers: 87.19.Wx, 87.57.Q
Highlights
Lung tumor motion is of great concern in radiotherapy
There is some difference between the CT number in the respiratory correlated (RC) mega voltage cone-beam computed tomography (MVCBCT) and the CT number that corresponds to the actual density of the material
Since the difference of motion quantification between different inserts is small, we present the average and standard deviation of the relative error in Table 5 by summarizing all the inserts belonging to the same type of RC MVCBCT scan
Summary
Among the respiratory compensation techniques presently used, respiratory gating based on external surrogates has the advantage of requiring no extra fluoroscopy imaging dose[1] or surgery to implant fiducials.[2,3] Our clinic uses a strain gauge to record respiratory phases and normalized amplitudes for 4DCT imaging. We analyze these images to determine the strain gauge phases to use for gating the treatment beam and limit the treated motion to less than 1 cm. Calibrating these surrogates to tumor motion would provide a more accurate beam-on trigger, this could require daily respiratory-correlated cone-beam (CB) CT imaging
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