Biomedical subjects

D H Hristov

Publications and source records attributed to D H Hristov.

4 recordsLinked to original sources

PubMed1999

Three-dimensional anatomy setup verification by correlation of orthogonal portal images and digitally reconstructed radiographs.

A method for three-dimensional verification of anatomy setup that uses the correlation of portal images and reference megavoltage digitally reconstructed radiographs (MDRRs) is presented. Prior to a treatment, an orthogonal pair of portal images is acquired from which subimages containing anatomical features are selected. These subimages are consequently matched to MDRRs that represent different rotations of the anatomy around axes going through the treatment isocenter. The Pearson correlation coefficient is employed for the matching since it is invariant with respect to global scaling and shifting of the image intensities. Furthermore, it does not require feature extraction or point-pair identification. The greatest value of the correlation coefficient corresponds to the proper rotational alignment of the anatomy and the location of the correlation maximum in each view indicates the translational shifts of the anatomy. The mean accuracy of translation and rotation registrations tests were a fraction of a millimeter and a fraction of a degree, respectively, for MDRR-to-MDRR matching. For portal-to-MDRR matching, the mean translation registration error is on the order of 1 mm and the mean error in radial displacement is of the order of 2.7 mm.

Algorithms↗

PubMed1998

A continuous penalty function method for inverse treatment planning.

Conventional inverse treatment planning attempts to calculate dose distributions that may not be feasible given the specified dose levels to various anatomical structures. A technique for inverse treatment planning has been developed that uses only target dose levels which are easily selectable to be feasible. A nonlinear constrained minimization problem is formulated to reflect the goal of sparing critical organs as much as possible while delivering a certain target dose within specified uniformity. The objective function is the squared dose delivered to critical organs. The constraints require the delivery of certain target dose within specified uniformity and non-negative pencil beam weights. A continuous penalty function method is introduced as a method for solving the large-scale constrained minimization problem. The performance of the continuous penalty function method is optimized by numerical investigation of few numerical integration schemes and a pair of weighting functions which influence the utility of the method. Clinical examples are presented that illustrate several features of the technique. The properties of the continuous penalty function method suggest that it may be a viable alternative to conventional inverse treatment planning.

Biophysical Phenomena↗

PubMed1997

An active set algorithm for treatment planning optimization.

An active set algorithm for optimization of radiation therapy dose planning by intensity modulated beams has been developed. The algorithm employs a conjugate-gradient routine for subspace minimization in order to achieve a higher rate of convergence than the widely used constrained steepest-descent method at the expense of a negligible amount of overhead calculations. The performance of the new algorithm has been compared to that of the constrained steepest-descent method for various treatment geometries and two different objectives. The active set algorithm is found to be superior to the constrained steepest descent, both in terms of its convergence properties and the residual value of the cost functions at termination. Its use can significantly accelerate the design of conformal plans with intensity modulated beams by decreasing the number of time-consuming dose calculations.

Algorithms↗

PubMed1996

A grey-level image alignment algorithm for registration of portal images and digitally reconstructed radiographs.

An algorithm for automatic registration of pairs of portal images based on image correlation is presented. It uses a fast-Fourier-transform-based cross-correlation operator to find the optimal registration, accounting for both in-plane translations and rotations. Different cross-correlation operators have been tested: the Pearson linear correlation coefficient has been implemented by fast Fourier transform and its performance has been compared to that of the more conventional normalized cross-correlation. A sequential approach has been applied to speed up the registration considerably without degrading the performance of the algorithm. The algorithm has also been applied to the automatic registration of portal images to digitally reconstructed radiographs (DRRs), which have been modified to resemble megavoltage images. The results are indicative of the feasibility of this approach to the inspection of patient setup in radiation therapy.

Algorithms↗