Comparison of Targeting Accuracy for Treatment Localization with Different CT Images of Moving Target in Thorax Region
Rattanaporn Sirichai BSc1, Benjamas Ngamching BSc1, Chirasak Khamfongkhruea MSc1, Sunanta Rojwatkarnjana MD1, Danupon Nantajit PhD2, Chirapha Tannanonta MSc1
Affiliation : 1 Department of Radiation Oncology, Chulabhorn Hospital, HRH Princess Chulabhorn College of Medical Science, Chulabhorn Royal Academy, Bangkok, Thailand 2 Faculty of Medicine and Public Health, HRH Princess Chulabhorn College of Medical Science, Chulabhorn Royal Academy, Bangkok, Thailand
Objective : To compare the accuracy of four different reconstruction techniques of Computed Tomography [CT] images for
localization of moving targets.
Materials and Methods : A respiratory motion phantom was simulated for tumor motion with the respiratory rate of 15
breaths per minute, breathing amplitude 1.0 cm in craniocaudal [CC] direction. In treatment room, the four different
reconstruction of CT image: free breath [FB], maximum intensity projection [MIP], mid-position [MidP] and average
intensity projection [AIP], were compared with the FB kV-Cone-Beam CT obtained from the on-board imaging system of
TrueBeam linear accelerator. The accuracy of target localization was calculated in terms of mean deviation and matching index
[MI]. Additionally, image quality and tumor shape were evaluated using visual grading analysis of 10 observers.
Results : The mean deviation of target position was significant in CC direction with the maximum value of 3.11+0.65 mm in
the MidP images. The high MI values were 0.86 and 0.87 in AIP and FB images, respectively. Moreover, AIP and FB had high
grading scores for both image quality and tumor shape.
Conclusion : Both FB and AIP image datasets can be used as the reference image for localizing the lung tumor with less than
2 cm movement in CC direction.
Keywords : 4DCT image acquisition, kV-CBCT, Moving target, Target localization
