Biomedical subjects

K A Langmack

Publications and source records attributed to K A Langmack.

7 recordsLinked to original sources

PubMed2001

Laser scanning of patient outlines for three-dimensional radiotherapy treatment planning.

In the planning of radiation treatments it is important to have a knowledge of the patient outline in order to correctly calculate the dose distribution that can be expected within the patient. This information is routinely obtained using x-ray computed tomography (CT). Although the CT data set is the ultimate data set, it can be impractical for economic and physical reasons. These impracticalities have been overcome using a commercial three dimensional (3D) laser scanning system. The system scans a laser line across the surface of the patient while a CCD camera views the patient from an offset angle. From a knowledge of the spatial orientation of the camera and the laser source, the system is able to detect the patient's surface and generate an equivalent 3D point cloud. Manipulation of 3D data sets allows the appropriate outlines of the patient to be obtained, that can then be used with the radiotherapy planning system. This has enabled the evaluation of 3D dose distributions for patients, and hence will allow the development of techniques for improving the uniformity of dose in breast treatments. The technique has no radiation overhead associated with it, is quick and is relatively cheap.

Breast↗

PubMed2001

Portal imaging.

Portal imaging is the acquisition of images with a radiotherapy beam. Imaging theory suggests that the quality of portal images could be much higher if the efficiency of the imaging media in detecting radiation could be improved. Introduction of new media (films and electronic portal imaging devices) has confirmed this by markedly increasing the quality of portal images. Images from these devices can then be used to verify a patient's treatment. Geometric verification requires the portal image to be registered with a reference image. Dosimetric verification requires the portal imager to be calibrated for dose. This review gives a brief overview of the current areas of interest in portal imaging: imaging theory; imaging media, film and electronic portal imaging devices; image registration; and dosimetry using these devices.

Humans↗

PubMed1999

Characterization of new portal film systems for radiotherapy verification.

Portal images are an important verification tool in radiotherapy. Their use has been limited by their poor image quality, which is due to the inherent lack of contrast at megavoltage energies. Recently CEA and Kodak have introduced new portal film-cassette systems with much improved contrast. We have determined the H-D curves for these systems and found the gamma (gamma) for the CEA system (8.5) to be larger than that for the Kodak EC-L system (6.3). The optimal doses were CEA TLF 1.2 cGy, CEA TVS 15.9 cGy and Kodak EC-L 1.5 cGy. We also obtained phantom images that were evaluated by 11 radiotherapists. They ranked the CEA B High Plus cassette with CEA TVS film the highest, followed by the Kodak EC-L system. Some clinical films of a lateral pelvis are also presented, to demonstrate the improvement in image quality with these new film systems as compared with conventional portal films.

Phantoms, Imaging↗

PubMed1998

An insight into the contributions of self-shielding and lamp reflectors to patient exposure in phototherapy units.

Calibration of phototherapy equipment can prove to be difficult. One problem is that the self-shielding produced by a patient reduces the irradiance relative to that determined when the cabinet is empty. A model has been developed to determine the factor to apply to the irradiance measured with the cabinet empty to give the irradiance with the patient present, i.e. the self-shielding correction factor. The model assumes that the cabinet consists of a number of discrete infinite line sources backed by perfect mirrors. The patient is treated as a barrier that prevents some of these sources being seen by the detector in the mirror it faces. The model was tested using a Waldmann 8001 K unit and three UV meters for UVA and UVB sources. The measurements suggested some modifications to the model--for UVA multiple reflections were important and for UVB the reflectors were only 30% efficient. The correction factors obtained were 0.87 for UVA and 0.96 for UVB.

Biophysical Phenomena↗

PubMed1998

An investigation into the use of carbon fibre for megavoltage radiotherapy applications.

Properties of carbon fibre of relevance to its use for megavoltage radiotherapy applications have been investigated. Measurements have been made of the percentage transmission and percentage build-up of carbon fibre at energies of 5, 6 and 8 MV. The results are presented in comparison with those obtained for other materials commonly used in radiotherapy: polymethylmethacrylate (PMMA), PETG copolyester and expanded polystyrene foam. It was found that carbon fibre has a higher percentage transmission and a lower percentage build-up than either PMMA or PETG copolyester. It was also found that the build-up due to a combination of carbon fibre and 5 cm of polystyrene foam was less than 65% over the energy range for which measurements were made, and much lower than that due to PETG copolyester. It is thus proposed that carbon fibre is a suitable material from which to make devices for use in megavoltage radiotherapy.

Calibration↗

PubMed1998

Characterization and use of a commercial n-type diode system.

The characteristics of n-type diodes (linearity, temperature, dose rate, radiation damage response, directional dependence, output factors, wedge factors and percentage depth dose determinations) were investigated. Subsequently, the diodes were used clinically for in vivo dose verification during external megavoltage photon beam therapy. It has been shown that n-type diodes are easy to use and the results obtained are comparable to those reported for p-type diodes. On most occasions, n-type diodes can be used without any additional correction factors apart from regular monthly calibration. There is good agreement between the uncertainty limits estimated from the diodes' characteristics and those obtained on the basis of 2261 patient measurements.

Equipment Failure↗

PubMed1995

The application of dose-volume histograms to the Paris and Manchester systems of brachytherapy dosimetry.

When the geometry of an implant does not exactly follow a system of dosimetry problems arise in choosing a treatment dose rate. This study has investigated the use of natural dose-volume histograms (DVHs) as a means for choosing the treatment dose level in these cases. A number of ideal geometrical cases have been investigated. For these, where appropriate, the Paris or Manchester dose rates have been calculated and compared with the peak position of the natural DVH. The dose rate at the peak of the DVH was found to agree with the basal dose rate calculated according to the Paris rules. For implants that completely obeyed the Paris rules the mean ratio was 1.009 +/- 4%. A series of clinical implants was also examined. For these the mean ratio was 1.002 +/- 2.5%. It is concluded that the peak position of a DVH can be used to predict the Paris basal dose rate of an implant. There was no systematic relationship found between the Manchester dose rate and the peak position of the DVH. The mean ratio between the Manchester dose rate and the peak dose rate position of the DVH was 0.82 +/- 13% for a series of implants.

Brachytherapy↗