Biomedical subjects

L Brewster

Publications and source records attributed to L Brewster.

9 recordsLinked to original sources

PubMed1995

Three dimensional conformal treatment planning with multileaf collimators.

PURPOSE: Three dimensional conformal radiation treatments are complex, often involving large numbers of blocked or multileaf collimated fields that shape regions of high dose to conform to the treatment volume. As manual definition and digitization of aperture shapes and their corresponding multileaf configurations can be impractically time consuming, it was necessary to integrate the planning of multileaf fields into an existing three dimensional treatment planning system and improve the efficiency of treatment delivery to make these treatments feasible on a routine basis. METHODS AND MATERIALS: A subfunction of the Beam's Eye View (BEV) component can be used to automatically generate a continuous aperture shape with a margin around the tumor to account for beam penumbra, and excluding any normal structures to be spared (each with its own margin). To convert a continuous aperture shape into one defined by the multileaf collimator (MLC), a leaf coverage mode is chosen to determine how leaves are fitted to aperture shapes. The conversion process also considers parameters of the specific MLC system, e.g., leaf thickness and the number of leaves. If normal structures to be shielded split the target into multiple regions, more than one multileaf aperture can result. An interactive leaf adjustment routine is also provided to allow for modification of individual leaf positions. Dose calculation programs then take into account multileaf apertures for computation of dose distributions using a pencil beam convolution model. Finally, prescription files specifying leaf and jaw configurations are prepared in treatment machine specific formats and downloaded to the computers driving the multileaf collimators and other components of the treatment machines. RESULTS AND CONCLUSION: An example is presented of a prostate treatment plan, with MLC configurations, dose distributions, and treatment delivery description, along with discussion of clinical implementation at Memorial Hospital.

Adenocarcinoma↗

PubMed1995

Phase I study of paclitaxel and topotecan in patients with advanced tumors: a cancer and leukemia group B study.

PURPOSE: To define the dose-limiting toxicities (DLTs) and the recommended phase II doses of paclitaxel combined with topotecan, without and with filgrastim support. PATIENTS AND METHODS: Patients with advanced solid tumors and a maximum of one prior chemotherapy regimen for metastatic disease were eligible if they had a performance status of 0 to 1 and normal renal, hepatic, and bone marrow function. Prior treatment with taxanes or comptothecin analogs, and prior pelvic irradiation were not allowed. Patients with a history of cardiac disease or on medications known to affect cardiac conduction were excluded. The dose of topotecan was fixed at 1.0 mg/m2/d for 5 days. The dose of paclitaxel was escalated until the maximum-tolerated dose (MTD), without and with filgrastim 5 micrograms/kg subcutaneously (SC) on days 6 to 14, was reached. Paclitaxel was administered over 3 hours on day 1 before topotecan. Treatment cycles were repeated every 21 days. RESULTS: Of 46 patients entered, 45 were assessable for toxicity and 34 for response. The principal toxicity was neutropenia. Without filgrastim, the MTD of paclitaxel was 80 mg/m2 on day 1 in combination with topotecan 1.0 mg/m2/d for 5 days. With filgrastim, the dose of paclitaxel was escalated to 230 mg/m2 in combination with the same dose of topotecan. At this dose level, one patient had hematologic DLT and a second patient developed neuromuscular DLT. Three patients had a partial response (PR): one with head and neck cancer, a second with non-small-cell lung cancer, and the third with colon cancer. CONCLUSION: We conclude that paclitaxel can be given at clinically relevant doses in combination with topotecan and filgrastim. The recommended dose for phase II studies is paclitaxel 230 mg/m2 on day 1 and topotecan 1.0 mg/m2/day for 5 days with filgrastim 5 micrograms/kg on days 6 to 14.

Adult↗

PubMed1991

Dose-volume histograms.

A plot of a cumulative dose-volume frequency distribution, commonly known as a dose-volume histogram (DVH), graphically summarizes the simulated radiation distribution within a volume of interest of a patient which would result from a proposed radiation treatment plan. DVHs show promise as tools for comparing rival treatment plans for a specific patient by clearly presenting the uniformity of dose in the target volume and any hot spots in adjacent normal organs or tissues. However, because of the loss of positional information in the volume(s) under consideration, it should not be the sole criterion for plan evaluation. DVHs can also be used as input data to estimate tumor control probability (TCP) and normal tissue complication probability (NTCP). The sensitivity of TCP and NTCP calculations to small changes in the DVH shape points to the need for an accurate method for computing DVHs. We present a discussion of the methodology for generating and plotting the DVHs, some caveats, limitations on their use and the general experience of four hospitals using DVHs.

Humans↗

PubMed1991

Histogram reduction method for calculating complication probabilities for three-dimensional treatment planning evaluations.

New tools are needed to help in evaluating 3-D treatment plans because of the large volume of data. One technique which may prove useful is the application of complication probability calculations. A method of calculating complication probabilities for inhomogeneously irradiated normal tissues is presented in this paper. The method uses clinical estimates of tolerance doses for a few discreet conditions of uniform partial organ irradiation, an empirical fit of a continuous function to these data, and a technique (the effective volume method) for transforming nonuniform dose-volume histograms into equivalent uniform histograms. The behavior of the effective volume histogram reduction method for various boundary conditions is reviewed. The use of complication probabilities in evaluating treatment plans is presented, using examples from an NCI 3-D treatment planning contract.

Humans↗

PubMed1991

Three-dimensional photon treatment planning of the intact breast.

Three-dimensional treatment planning for the intact breast was performed on two patients who had undergone CT scanning. A total of 38 treatment plans were evaluated. Multiple plans were evaluated for each patient including plans with and without inhomogeneity corrections, plans using varying photon energies of 60Co, 4 MV, 6 MV, 10 MV, and 15 MV, and three-dimensionally unconstrained plans. Increased hot spots were appreciated in the central axis plane when lung inhomogeneity corrections were used. Additional hot spots were appreciated in off-axis planes towards the cephalad and caudad aspects of the target volume because of lung inhomogeneity corrections and changes in the breast contour. The use of 60Co was associated with an increase in the magnitude and volume of hot spots, whereas the use of higher energy photons such as 10 MV and 15 MV was associated with an unacceptable target coverage at shallow depths. Therefore, for the two patients studied, the use of a medium energy photon beam (such as from a 6 MV linear accelerator) appeared to be the energy of choice for treatment of the intact breast. The three-dimensionally unconstrained plans were able to improve slightly upon the standard plans, particularly with relationship of dose to normal tissue structures. Areas for future research were identified, including the use of tissue compensators.

Adult↗

PubMed1991

Three-dimensional treatment planning for postoperative treatment of rectal carcinoma.

The role of three-dimensional (3-D) treatment planning for postoperative radiation therapy was evaluated for rectal carcinoma as part of an NCI contract awarded to four institutions. It was found that the most important contribution of 3-D planning for this site was the ability to plan and localize target and normal tissues at all levels of the treatment volume, rather than using the traditional method of planning with only a single central transverse slice and simulation films. There was also a slight additional improvement when there were no constraints on the types of plans (i.e., when noncoplanar beams were used). Inhomogeneity considerations were not important at this site under the conditions of planning, i.e., with energies greater than 4 MV and multiple fields. Higher beam energies (15-25 MV) were preferred by a small margin over lower energies (down to 4 MV). The beam's eye view and dose-volume histograms were found quite useful as planning tools, but it was clear that work should continue on better 3-D displays and improved means of translating such plans to the treatment area.

Combined Modality Therapy↗

PubMed1986

Respiratory disability in ex-flax workers.

Acute respiratory effects occur in a high proportion of subjects exposed to textile dusts. The extent to which these lead to permanent respiratory symptoms and loss of lung function is unknown. A survey of random population samples was therefore conducted in ten towns in Northern Ireland in which flax processing had been a major source of employment. The MRC questionnaire on respiratory symptoms was administered and Vitalograph tracings recorded on subjects aged 40 to 74 inclusive. An occupational history was taken at the end of each interview. Lung function in ex-flax workers was slightly lower than in control subjects never exposed to flax dust, but the presence of a positive interaction with age meant that differences were apparent only in the younger subjects. Over about the age of 65 the lung function in the ex-flax workers was comparable with that of the controls and overall the loss was at most about half that due to light smoking (1-14 cigarettes a day). The association between a "dust exposure score" and lung function was inconsistent in the two sexes. In men there was a small decrement with increasing dust exposure. In women there was also a small decrement, but a positive interaction with age meant that the women with the highest dust exposure scores had a lower loss with increasing age than the women with the least dust exposure. There was an excess in symptoms in the ex-flax workers but the size of the excess was greater than would be expected from the lung function results. It is possible that, although the survey was conducted without explicit reference to the flax industry, knowledge throughout Northern Ireland that many flax workers have been awarded compensation on the grounds of respiratory disablement may have led to an increased reporting of symptoms in the ex-flax workers.

Adult↗

PubMed1978

Early detection of childhood hearing impairment - problems and possible solutions.

The identification of infants with profound hearing loss is a complex task, and one that is beset with problems. This paper discusses some of these problems and points out a few of the ways by which, hopefully, they are coming closer to solution. The first problem results from the nature of the beast, which seems to have so many social, medical, educational, and political implications. There are also some problems with the high risk register and with screening for hearing loss; but probably the most disturbing are the conflicts that arise between professionals when their aims, objectives, and methods don't quite match. Current progress in the linking up of high risk and screening methodologies is discussed, as well as ways in which existing health care systems can be utilized in deafness detection.

Audiology↗

PubMedDate not supplied

Automatic generation of beam apertures.

In order to specify arbitrarily shaped beam apertures for three-dimensional radiation treatment planning, aperture contours (or outlines) are often manually drawn using a beam's eye view display of the target volume and nearby normal structures. This can be a very time consuming process, and can be impractical for multileaf collimation and computer-aided optimization of a large number of fields. A method has been developed that allows automatic generation of aperture shapes that outline the target volume and may spare neighboring structures whenever desired. Margins of user-specified sizes (positive or negative) around the target and normal structures are also incorporated. For a chosen beam orientation, a 3D surface of each anatomic structure of interest is formed and projected onto a plane at the beam's isocenter. The outlines of each projected object are detected by an edge following algorithm, and margins are added. The outlines of normal structures are combined with that of the target volume to obtain the final aperture shape. This is done by overlaying filled versions of the outlines in such a way that regions of the target overlapped by normal structures are cut away, leaving only the target volume region to be irradiated. The remaining target volume outline is again detected to produce an aperture contour. Normal structures may split the aperture into several pieces, so this method detects any number of disjoint aperture contours. The results of the algorithm are illustrated with apertures generated for nasopharynx and prostate tumors, including sparing of normal tissues.

Algorithms↗