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Biomedical subjects

R G Lane

Publications and source records attributed to R G Lane.

At least 19 recordsLinked to original sources
PubMed1992

Custom beam profiles in computer-controlled radiation therapy.

A computer-controlled radiation therapy technique is demonstrated which uses multiple concurrent boost fields to modify the beam profile of a conventional treatment beam. A principal field, identical to that of a corresponding conventional treatment plan, delivers the major component of the prescribed dose. Dose increments given from boost fields placed within this principal field compensate for variations in patient anatomy, for variations in target volume shape, and/or for imperfect beam characteristics, such as excessive off-axis dose or inadequate beam wedge angle. This concurrent boost field technique is demonstrated for several treatment sites. It produces significant improvement in uniformity of dose delivered to the target compared to conventional treatment. Implementation of these treatments requires a computer-controlled linear accelerator with independently-movable collimator jaws, an automatic beam set-up procedure, and a patient prescription database. Since all fields are delivered under computer control, concurrent boost technique treatment times are not much longer than those of conventional treatments.

Feasibility Studies↗
PubMed1991

Treatment planning optimization using constrained simulated annealing.

A variation of simulated annealing optimization called 'constrained simulated annealing' is used with a simple annealing schedule to optimize beam weights and angles in radiation therapy treatment planning. Constrained simulated annealing is demonstrated using two contrasting objective functions which incorporate both biological response and dose-volume considerations. The first objective function maximizes the probability of a complication-free treatment (PCFT) by minimizing the normal tissue complications subject to the constraint that the entire target volume receives a prescribed minimum turmourcidal dose with a specified dose homogeneity. Probabilities of normal tissue complication are based on published normal tissue complication probability functions and computed from dose-volume histograms. The second objective function maximizes the isocentre dose subject to a set of customized normal tissue dose-volume and target volume dose homogeneity constraints (MVDL). Although the PCFT objective function gives consistently lower estimates of normal tissue complication probabilities, the ability to specify individualized dose-volume limits, and therefore the individualized probability of complication, for an individual organ makes the MDVL objective function more useful for treatment planning.

Esophageal Neoplasms↗
PubMed1990

Constrained simulated annealing for optimized radiation therapy treatment planning.

A variation of simulated annealing optimization called 'constrained simulated annealing' is used with a simple annealing schedule to automatically optimize beam weights and beam angles in radiation therapy treatment planning. This optimization technique permits the straightforward utilization of any objective function and any set of dose constraints, even those described by non-analytic functions. Constrained simulated annealing is demonstrated using an objective function which minimizes the probability of normal tissue complications subject to the constraint that the entire target volume receive a tumoricidal dose within specified maximum and minimum limits. Target volume dose constraints are determined by points located on the perimeter of the target volume. Probabilities of normal tissue complications are based on published normal tissue complication probability functions and computed from dose-volume histograms calculated on points spread throughout the normal anatomy.

Algorithms↗
PubMed1990

The influence of dose constraint point placement on optimized radiation therapy treatment planning.

To efficiently use linear and quadratic programming for treatment planning optimization on a routine basis, automated methods are needed for placing dose constraint points. We have investigated, for linear programming optimization, the minimum number of constraint points needed to achieve an acceptable approximation to the desired (ideal) solution. Seven different constraint point placement algorithms were evaluated for a given objective function. One of these algorithms was chosen for routine clinical use at our institution. This algorithm places constraint points on the perimeter of the target volume and on the perimeter and in the interior of each normal structure. Additional points are placed on the perimeter of a constant thickness buffer region surrounding the target volume. Excellent optimization results are obtained with 40-70 constraint points per treatment planning slice.

Computer Simulation↗
PubMed1990

Improved dose homogeneity in the head and neck using computer controlled radiation therapy.

Computer-controlled radiation therapy techniques are demonstrated which improve dose homogeneity throughout the nasopharynx when compared to conventional treatment techniques. The typical approach using a heavily weighted anterior field and opposed wedged lateral fields results in a dose gradient from 95% to 110% or greater. All three of the computer-controlled techniques investigated improved the dose uniformity to a range from 95% to 105% or less. Multiple overlapping fields are used to compensate for patient anatomy and treatment beam characteristics. Treatment planning and monitor unit calculations are quite time-consuming at this stage of development. Actual treatment time is not unreasonably long and can be improved in future releases of the therapy machine control software.

Humans↗
PubMed1990

Uncertainty in dose estimation for gynecological implants.

One source of uncertainty in doses computed for intracavitary gynecological applications is the imprecision inherent in localizing the sources and the points of interest on radiographs of the implant and in transferring that data into the treatment planning computer. To quantify the effect of these activities on the accuracy of computed doses, five physicists and two dosimetrists performed computerized dose calculations on five applications chosen randomly from our patient files. For each of these applications, doses were computed at the traditional points A and B and at points in the bladder and rectum. Using identical sets of films, each planner located both the radioactive sources and points of interest, or only the sources, or only the points of interest. Another set of films was used to measure the accuracy of digitizing alone. Planners received no instructions on either the definition or the placement of the points of interest. Overall uncertainties in computed doses to points A and B and bladder were found to be about 7%. Uncertainty in dose to the rectum was on the order of 50%. Analysis of the results showed that about 1% of the error was due to digitization and about 2% to identification of source locations. Among the individual planners, almost all of the dose variation was from differences in placement of the points of interest on the implant radiographs. The results demonstrate the need for standard definitions and locations for points of calculation so that meaningful comparisons can be made among institutions.

Brachytherapy↗
PubMed1978

A whole body repositioning system.

A versatile and easily used whole body repositioning system is described. It may be quickly and inexpensively constructed. The system has been found to be particularly helpful in the extended field treatment of Hodgkin disease, head and neck treatments, and in tumors of the abdomen and pelvis.

Radiotherapy↗
PubMed1978

Electron beam calibration constants.

Electron treatment beam calibration constants are tabulated in a convenient form for mean incident electron energies, Eo, of 6 to 21 MeV; and practical reanges, Rp, of 2.75 to 10.53 cm of water. Values of mean electron energy at depth Ed, chamber radius correction factors (Kp), and CE factors may be readily obtained from this chart.

Electrons↗
PubMed1977

A tissue compensation source-to-skin measurement system.

An easy to use, low-cost system for measuring the source-to-skin distance used in determining tissue compensation requirements is described. These measurements can be performed with accuracy and precision for any treatment field size and at any treatment beam angle. The system can be used in conjuction with several different tissue compensation methods.

Humans↗
PubMed1975

Extended field treatment flatness filter for 4 MV linear accelerators.

An auxiliary flatness filter for large field treatment on 4 MV linear accelerator provides an isodose distribution which does not vary more than 6% over the central 80% of the axis of a 32 x 32-cm field at 80 cm in air, and at a 2.5, 6, and 12-cm depth in water. This lead disc filter does not affect the central axis depth dose values, and results in only a 16% reduction in dose rate on the central field axis.

Radiotherapy, High-Energy↗
PubMed1975

A wedge filter interlock system for 4 MV linear accelerators.

The wedge filter interlock system on a 4 MV linear accelerator was modified to ensure proper selection and placement of filter. By using a series of microswitches to replace the two-pin connection for each wedge, proper placement of the wedge in the treatment beam was ensured. Both the chain and plug were eliminated by using a 6 pole, 6 position sub-miniature rotary switch to produce the remaining connections.

Filtration↗
PubMed1975

Malfunction of linear accelerator dose monitoring systems.

Malfunctions of the dose monitoring systems of two linear accelerators were studied. A variation of plus or minus 2.5% over an air density correction factor range from 1.02 to 1.07 was measured, suggesting that the ionization-type monitor chambers were open to the atmosphere. An average variation of minus 2.0% was present between early morning calibrations and those performed later in the day. Any variation caused by changes in control console temperature was within experimental error. This type of malfunction can lead to errors in delivered doses of 5%.

Electrons↗