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Xu QY , He ZJ , Fan JJ , Hamilton RJ , Chen Y , Ma CM , Xing L
Registration of on-board X-ray images with 4DCT: A proposed method of phase and setup verification for gated radiotherapy
Physica Medica. 2010 Jul;26(3) :117-125
PMID: ISI:000280471600001   
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Current gated radiation therapy starts with simulation 4DCT images of a patient with lung cancer. We propose a method to confirm the phase of 4DCT for planning and setup position at the time of treatment. An intensity-based rigid algorithm was developed in this work to register an orthogonal set of on-board projection X-ray images with each phase of the 4DCT. Multiple DRRs for one of ten 4DCT phases are first generated and the correlation coefficient (CC) between the projection X-ray image and each DRR is computed. The maximum value of CC for the phase is found via a simulated annealing optimization process. The whole process repeats for all ten phases. The 4DCT phase that has the highest CC is identified as the breathing phase of the X-ray. The phase verification process is validated by a moving phantom study. Thus, the method may be used to independently confirm the correspondence between the gating phase at the times of 4DCT simulation and radiotherapy delivery. When the intended X-ray phase and actual gating phase are consistent, the registration of the DRRs and the projection images may also yield the values of patient shifts for treatment setup. This method could serve as the 4D analog of the conventional setup film as it provides both verification of the specific phase at the time of treatment and isocenter positioning shifts for treatment delivery. (C) 2009 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
Xu, Qianyi He, Zhijun Fan, Jiajin Hamilton, Russell J. Chen, Yan Ma, C. -M. Xing, Lei Susan Komen Breast Cancer Foundation [BCT0504071] LX wishes to thank Dr. Eduard Schreibmann from Emory University for useful discussions. He also acknowledges a grant support from the Susan Komen Breast Cancer Foundation (BCT0504071). 31 Ist editoriali polgrafici int; casella postale n 1, succursale n 8, 56123 pisa, italy 633al