Biomedical subjects

Dragan Tubic

Publications and source records attributed to Dragan Tubic.

4 recordsLinked to original sources

PubMed2006

Octree indexing of DICOM images for voxel number reduction and improvement of Monte Carlo simulation computing efficiency.

The purpose of the present study is to introduce a compression algorithm for the CT (computed tomography) data used in Monte Carlo simulations. Performing simulations on the CT data implies large computational costs as well as large memory requirements since the number of voxels in such data reaches typically into hundreds of millions voxels. CT data, however, contain homogeneous regions which could be regrouped to form larger voxels without affecting the simulation's accuracy. Based on this property we propose a compression algorithm based on octrees: in homogeneous regions the algorithm replaces groups of voxels with a smaller number of larger voxels. This reduces the number of voxels while keeping the critical high-density gradient area. Results obtained using the present algorithm on both phantom and clinical data show that compression rates up to 75% are possible without losing the dosimetric accuracy of the simulation.

Algorithms↗

PubMed2005

Sliding slice: a novel approach for high accuracy and automatic 3D localization of seeds from CT scans.

We present a conceptually novel principle for 3D reconstruction of prostate seed implants. Unlike existing methods for implant reconstruction, the proposed algorithm uses raw CT data (sinograms) instead of reconstructed CT slices. Using raw CT data solves several inevitable problems related to the reconstruction from CT slices. First, the sinograms are not affected by reconstruction artifacts in the presence of metallic objects and seeds in the patient body. Second, the scanning axis is not undersampled as in the case of CT slices; as a matter of fact the scanning axis is the most densely sampled and each seed is typically represented by several hundred samples. Moreover, the shape of a single seed in a sinogram can be modeled exactly, thus facilitating the detection. All this allows very accurate 3D reconstruction of both position and the orientation of the seeds. Preliminary results indicate that the seed position can be estimated with 0.15 mm accuracy (average), while the orientation estimate accuracy is within 3 deg on average. Although the main contribution of the paper is to present a new principle of reconstruction, a preliminary implementation is also presented as a proof of concept. The implemented algorithm has been tested on a phantom and the obtained results are presented to validate the proposed approach.

Algorithms↗

PubMed2004

Idealized line source configuration for permanent 125I prostate implants.

BACKGROUND AND PURPOSE: To validate the use of idealized seed orientations in conjunction with the line source formalism for post-implant dosimetry of permanent 125I prostate implants. PATIENTS AND METHODS: Post-implant, a CT scan and three fluoroscopic images were obtained for 32 patients having undergone permanent implants. From these images, the seed positions and orientations (phi,theta) were determined (1625 individual seeds). Two different dosimetric calculations were done: one using real orientations and one using idealized orientations (seeds along the axis of implantation). Dose volume histograms (DVHs) and key dosimetric parameters were compiled for the prostate, urethra, rectum, bladder and penile bulb, to evaluate the difference between the two approximations. RESULTS: The phi angle distribution (phi = 1.1 degrees; sigma phi = 22.9 degrees) and the theta angle distribution (theta= -4.29 degrees; sigma theta = 27.1 degrees) were found to be similar to the first order except for the pronounced peak of the phi angle distribution. The DVHs comparison and dosimetric parameters study reveal no significant difference between the two approximations. The difference in D90 for the prostate was only 0.02% (sigma = 0.91%) The differences were slightly higher in the case of the organs at risk, as expected from the dosimetric characteristics of the seed model used. CONCLUSIONS: The angular distributions (phi,theta) of individual seeds were determined. The dosimetric evaluation shows that line source formalism can be used in conjunction with an idealized seed configuration presented here to report prostate and organs at risk dose coverage.

Brachytherapy↗

PubMed2003

Automatic post-implant needle reconstruction algorithm to characterize and improve implant robustness analyses.

Post-implant analysis in permanent implant brachytherapy is an important process that provides a feedback on treatment quality. Random seed movements, edema, and needle related factors contribute to deteriorate dose coverage. For a complete study of these movements, it is important to reconstruct the post-implant seeds clusters but, up to now, this task was only possible via a long and difficult manual process. To facilitate post-implant analysis a simulated annealing algorithm was developed to perform automatic reconstructions. This process is fast (30-60 s on a 1.3 GHz pentium) and has a high level of success, even with up to 5% of seed loss. Tests on 21 clinical cases show that the algorithm yields exactly the same results as manual reconstructions. A realistic simulation tool was used to generate 58 synthetic post-implant data, in which cases the exact configuration was known. Even if some errors were found, pertinent information was extracted. For medium seed density [corresponding to seeds of 0.6 mCi (0.762 U)], 97% of seeds are matched with their correct needle and 89% are matched with their correct planned position. This method provides pertinent information that can be used to understand inhomogenous dose coverage in specific prostate quadrants; to make realistic post-implant simulations or to identify seeds belonging to a needle loaded with different seed types or activity.

Algorithms↗