Image-Guided Radiotherapy in Near Real Time With Intensity-Modulated Radiotherapy Megavoltage Treatment Beam Imaging

Department of Radiation Oncology, Stanford University, Palo Alto, CA, USA.
International journal of radiation oncology, biology, physics (Impact Factor: 4.26). 11/2009; 75(2):603-10. DOI: 10.1016/j.ijrobp.2009.04.068
Source: PubMed

ABSTRACT To utilize image-guided radiotherapy (IGRT) in near real time by obtaining and evaluating the online positions of implanted fiducials from continuous electronic portal imaging device (EPID) imaging of prostate intensity-modulated radiotherapy (IMRT) delivery.
Upon initial setup using two orthogonal images, the three-dimensional (3D) positions of all implanted fiducial markers are obtained, and their expected two-dimensional (2D) locations in the beam's-eye-view (BEV) projection are calculated for each treatment field. During IMRT beam delivery, EPID images of the megavoltage treatment beam are acquired in cine mode and subsequently analyzed to locate 2D locations of fiducials in the BEV. Simultaneously, 3D positions are estimated according to the current EPID image, information from the setup portal images, and images acquired at other gantry angles (the completed treatment fields). The measured 2D and 3D positions of each fiducial are compared with their expected 2D and 3D setup positions, respectively. Any displacements larger than a predefined tolerance may cause the treatment system to suspend the beam delivery and direct the therapists to reposition the patient.
Phantom studies indicate that the accuracy of 2D BEV and 3D tracking are better than 1 mm and 1.4 mm, respectively. A total of 7330 images from prostate treatments were acquired and analyzed, showing a maximum 2D displacement of 6.7 mm and a maximum 3D displacement of 6.9 mm over 34 fractions.
This EPID-based, real-time IGRT method can be implemented on any external beam machine with portal imaging capabilities without purchasing any additional equipment, and there is no extra dose delivered to the patient.

Download full-text


Available from: Gary Luxton, Sep 28, 2015
1 Follower
33 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Rigorous studying of transfer of energy and behaviour of a wavefront in simulated fractal medium is based on application of new differintegral model of a space-time source. The relations featuring behaviour are considered α-form of wave packets, the wavefronts produced by a pulsed source.
    Ultrawideband and Ultrashort Impulse Signals, 2004 Second International Workshop; 10/2004
  • [Show abstract] [Hide abstract]
    ABSTRACT: To assess the current status and technological advances in image-guided external beam radiotherapy for prostate cancer. Modern imaging has improved the ability to define radiotherapy target volumes. Specifically, treatment margins have been reduced through the use of treatment planning and image-guidance technology. Increasing dose has led to increased disease control. Concurrent technological advances may improve treatment-related toxicity. Data continues to emerge on patient selection, treatment schedule, and use of additional systemic therapy in conjunction with radiation. In the present article, we review recent developments in radiation planning, image guidance, patient selection and fractionation, dose escalation, toxicity, systemic therapy, and follow-up.
    Current opinion in urology 02/2010; 20(3):223-8. DOI:10.1097/MOU.0b013e32833817aa · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In-treatment fiducial tracking has recently received attention as a method for improving treatment accuracy, dose conformity, and sparing of healthy tissue. 3-D fiducial localization in arc-radiotherapy remains challenging due to the motion of targets and the complexity of arc deliveries. We propose a novel statistical method for estimating 3-D fiducial motion using limited 2-D megavoltage (MV) projections. 3-D fiducial motion was estimated by a maximum a posteriori (MAP) approach to integrating information of fiducial projections with prior knowledge of target motion. To obtain the imaging geometries, short sequences of MV projections were selected in which fiducials were continuously visible. The MAP algorithm estimated the 3-D motion by maximizing the probability of displacement of fiducials in the sequences. Prior knowledge of target motion from a large statistical sample was built into the model to enhance the accuracy of estimation. In the case that a motion prior was unavailable, the algorithm can be simplified to the maximum likelihood (ML) approach. To compare tracking performance, a multiprojection geometric method was also presented by extending the typical two-project ion geometric estimation approach. The algorithms were evaluated using clinical prostate motion traces, and the performance was measured in quality indices and statistical evaluation. The results showed that the MAP method significantly outperforms the geometric method in all measures. In our simulations, the MAP method achieved an accuracy of less than 1 mm RMS error using only five continuous projections, whereas the geometric method required 15 projections to achieve a similar result. The approach presented can accurately estimate tumor motion using a limited number of continuous projections. The MAP motion estimation is superior to both the ML and geometric estimation methods.
    Medical Physics 06/2011; 38(6):3222-31. DOI:10.1118/1.3584197 · 2.64 Impact Factor
Show more