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Improvements to the Computational Environment for Radiotherapy Research

A Apte

Aditya P. Apte*, Ya Wang, Joseph O. Deasy, Memorial Sloan Kettering Cancer Center, New York, NY

SU-E-J-87 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To present new tools in CERR to analyze image registration, as well as other software updates and additions.

Method: Two new features were added to CERR to evaluate the accuracy of image registration: (1) gamma-based metric for comparing base and registered scans: All scan quantitative scan-comparison methods rely on using image intensities. This means, these methods cannot quantify spatial misalignment between base and registered images. The gamma metric (similar to the ones used for dose comparisons) was modified for image-comparisons. (2) a color-coded mirror grid, based on mutual information or mean-square-error metrics: Color-coding blocks within the grid help users focus on the well vs. poorly registered areas. In addition to these features, other noteworthy additions to CERR include (1) the ability to use colormaps for scans. This is an improvement over grayscale-only scan display and is particularly useful for images produced in nuclear medicine. (2) the ability to change scan-windowing by dragging the mouse along a view, similar to PACS viewers. Interactive windowing is particularly useful while delineating structures. (3) The ability to import Image-annotations. The DICOM modality PR is used to store graphical and text annotations for images. These are widely used in diagnostic radiology and could be extracted from PACS. CERR can now imports these objects and store them under the planC{indexS.GSPS} element.

Results: A 3-d gamma metric was implemented in CERR for comparing image registration. It was evaluated on prostate cancer registration with criteria of 4mm and 50HU. The fused images were compared against the Gamma metric map. It was observed that the regions that matched up poorly had gamma value above 1.

Conclusion: A novel gamma based approach to compare image registration allows for specification of acceptance criteria. Features added to CERR increase its utility in ART, registration, segmentation and collaboration.

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