Abstract
Image-guided radiotherapy (IGRT), adaptive radiotherapy (ART), and online reoptimization rely on accurate mapping of the radiation beam isocenter(s) from planning to treatment space. This mapping involves rigid and/or nonrigid registration of planning (pCT) and intratreatment (tCT) CT images. The purpose of this study was to retrospectively compare a fully automatic approach, including a non-rigid step, against a user-directed rigid method implemented in a clinical IGRT protocol for prostate cancer. Isocenters resulting from automatic and clinical mappings were compared to reference isocenters carefully determined in each tCT. Comparison was based on displacements from the reference isocenters and prostate dose-volume histograms (DVHs). Ten patients with a total of 243 tCTs were investigated. Fully automatic registration was found to be as accurate as the clinical protocol but more precise for all patients. The average of the unsigned x, y, and z offsets and the standard deviations (σ) of the signed offsets computed over all images were (avg. ± σ (mm)): 1.1 ± 1.4, 1.8 ± 2.3, 2.5 ± 3.5 for the clinical protocol and 0.6 ± 0.8, 1.1 ± 1.5 and 1.1 ± 1.4 for the automatic method. No failures or outliers from automatic mapping were observed, while 8 outliers occurred for the clinical protocol.
Highlights
Image-guided radiotherapy (IGRT) [1], off-line adaptive radiotherapy (ART) [2], and online reoptimization [3] involve pretreatment imaging, taken here to be CT imaging
The rationale for using a model to map the isocenter stems from several considerations: (1) during planning the isocenter is positioned relative to the prostate; (2) a point in an image can be more accurately found by relying on regional image features that are correlated spatially with the point rather than using local information near the point itself [18]; and (3) the trainable models used in this study provide a means for determining both the rigid and nonrigid components of the mapping transformation
The fully automatic mapping algorithm is as accurate as the clinical protocol but more precise
Summary
Image-guided radiotherapy (IGRT) [1], off-line adaptive radiotherapy (ART) [2], and online reoptimization [3] involve pretreatment imaging, taken here to be CT imaging. A procedure held in common by all three methods is registration of the planning (pCT) and treatment (tCT) images to map the planned isocenter to treatment space. Accuracy and precision of this step are important for delivering an accumulated dose distribution that closely matches the treatment plan. Mapping methods involve at least rigid registration. A nonrigid step would be included to account for differences in organ shape between planning and treatment times (Figure 1). The composite of the rigid, and possibly nonrigid, matrices is used to map the planned isocenter to the tCT
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
