Biomedical subjects

L H Lanzl

Publications and source records attributed to L H Lanzl.

At least 19 recordsLinked to original sources

PubMed1998

A simple algorithm for planar image registration in radiation therapy.

A simple algorithm is presented for planar image registration and the method is applied to the simulator and portal image registration for patient setup verification in radiation therapy. Basically, the algorithm follows the concept proposed by Balter et al. [Med. Phys. 19, 329-334 (1992)], which converts the problem of open curve registration into matching a series of points along the curves. Balter's algorithm consists of three steps: (1) to determine a common starting point for each curve pair, (2) acquire two corresponding point sets along each curve, and (3) obtain a global transform matrix by matching two point sets. We integrate all three steps into one simple procedure which fits the sampled points along the intended curve pair by taking the relative path length shift as an independent fitting parameter. After being modified, the algorithm is able to take the different magnification factors of images into account, and it avoids curvature calculations. Numerical simulation as well as clinical and phantom images have been utilized to test the accuracy of the algorithm. The typical errors are less than 1 mm in translation and 1 degree in rotation. We also made a comparison study with the chamfer method. The results of the two methods agree to within 0.5 mm in translation and 0.5 degree in rotation.

Algorithms↗

PubMed1997

A method for more efficient source localization of interstitial implants with biplane radiographs.

The conventional method for source localization in an interstitial ribbon implant by means of biplane radiographs can be difficult, especially when a large number of seeds are involved. We present a new algorithm for more efficient source localization with the same conventional biplane radiographs. The method does not require a one-to-one source correspondence between two radiographs. The user needs only to digitize several points, following the shape of each ribbon from both films. The points that are digitized do not need to be the location of the seeds, and they do not have to correspond to the same points on both films. The algorithm uses the multidimensional minimization method to reconstruct the three-dimensional locus of the ribbon. The location of each seed is then determined by its pathlength relative to the corresponding starting point. We have used phantom experiments and clinical cases to test the reliability of the algorithm. The results show that the errors in the determination of seed locations are less than 2 mm, and the efficiency in source digitization for data entry can be increased by a factor up to 5.

Biophysical Phenomena↗

PubMed1990

Retrospective analysis of hyperthermia for use in the palliative treatment of cancer: a multi-modality evaluation.

Forty-two patients with local or superficial metastatic or recurrent malignant tumors were treated in a non-randomized Phase I/II study to assess the tumoricidal effects of heat combined with radiation and/or chemotherapy. Radiation doses administered averaged 3130 +/- 350 cGy; chemotherapeutic agents employed included bleomycin, mitomycin-C, adriamycin, and cis-platin, heat was induced by radiative or interstitial microwave applicators operating at frequencies ranging from 95 to 900 MHz. Forty-one of the forty-two patients were evaluated for initial therapeutic effects yielding the following response distributions: local hyperthermia with radiation--42% complete response (CR), 44% partial response (PR), and 15% no response (NR); local hyperthermia with chemotherapy--0% CR, 50% PR and 50% NR. Long-term response duration was evaluated for local hyperthermia with radiation, yielding mean time to recurrence of 9.4 months for CR's and mean time to progression of 3.4 months for PR's. In retrospective analysis, we examined the correlations of previously established response-predictor variables of tumor volume and minimum thermal dose with both initial and long-term response rates. Initial complete response rates were correlated directly with non-site-specific minimum thermal dose, varied inversely with tumor volume and exhibited a positive correlation for a limited histologic type/treatment site combination. Surprisingly, long-term response did not correlate either with tumor volume or thermal dose. The frequency of thermally induced complications, which did not correlate with any measured thermal parameters, was found to be 42%, expressed on a per-patient basis.

Adult↗

PubMed1982

World radiation therapy dosimetry network.

The ultimate responsibility for the standardization of radiation exposures and doses within a country lies with the country's national standardizing laboratory, provided that the country has such a laboratory. In the late 1960's, only 17 countries had primary national standards laboratories, whereas more than 100 countries did not. Therefore, the International Atomic Energy Agency undertook a program of developing a network of secondary standards dosimetry laboratories (SSDL) and was later joined in the project by the World Health Organization. By 1982, the network consisted of SSDL's in 35 countries. The United States has three secondary or regional dosimetry laboratories for instrument calibration traceable to the U.S. National Bureau of Standards. Studies of radiation responses of biological systems, including normal and tumor tissue, provide information on the accuracy of dose measurements required for assessment of these responses.

International Cooperation↗

PubMed1976