Biomedical subjects

M C Ferris

Publications and source records attributed to M C Ferris.

6 recordsLinked to original sources

PubMed2003

A toolbox for intensity modulated radiation therapy optimization.

We have designed a toolbox that provides an environment for testing radiotherapy optimization techniques, objective functions, and constraints. A set of three-dimensional (3D) pencil beam dose distributions have been computed for a cylindrical phantom. The 6 MV pencil beams were computed using a superposition-based dose engine commissioned for an Elekta SL20 linear accelerator. Due to the cylindrical symmetry of the phantom, the pencil beam dose distributions for any arbitrary beam angle can be determined by simply rotating the pencil beam data sets. Thus, the full accuracy is maintained without the need for additional dose calculations or large data storage requirements. In addition to the pencil beam data sets, tools are included for (1) rotating the pencil beams, (2) calculating the beam's eye view, (3) drawing structures, (4) writing the pencil beam dose data out to the optimizer, and (5) visualizing the optimized results. The pencil beam data sets and the corresponding tools are available for download at http://medschool.umaryland.edu/departments/radiationoncology/pencilbeam/. With this toolbox, researchers will have the ability to rapidly test new optimization techniques and formulations for intensity modulated radiation therapy and 3D conformal radiotherapy.

Algorithms↗

PubMed2001

An iterative sequential mixed-integer approach to automated prostate brachytherapy treatment plan optimization.

Conventional treatment planning for interstitial prostate brachytherapy is generally a 'trial and error' process in which improved treatment plans are generated by iteratively changing, via expert judgement, the configuration of sources within the target volume in order to achieve a satisfactory dose distribution. We have utilized linear mixed-integer programming (MIP) and the branch-and-bound method, a deterministic search algorithm, to generate treatment plans. The rapidity of dose falloff from an interstitial radioactive source requires fine sampling of the space in which dose is calculated. This leads to a large and complex model that is difficult to solve as a single 3D problem. We have therefore implemented an iterative sequential approach that optimizes pseudo-independent 2D slices to achieve a fine-grid 3D solution. Using our approach, treatment plans can be generated in 20-45 min on a 200 MHz processor. A comparison of our approach with the manual 'trial and error' approach shows that the optimized plans are generally superior. The dose to the urethra and rectum is usually maintained below harmful levels without sacrificing target coverage. In the event that the dose to the urethra is undesirably high, we present a refined optimization approach that lowers urethra dose without significant loss in target coverage. An analysis of the sensitivity of the optimized plans to seed misplacement during the implantation process is also presented that indicates remarkable stability of the dose distribution in comparison with manual treatment plans.

Algorithms↗

PubMed2000

Inverse treatment planning for Gamma Knife radiosurgery.

An inverse treatment planning system for Gamma Knife radiosurgery has been developed using nonlinear programming techniques. The system optimizes the shot sizes, locations, and weights for Gamma Knife treatments. In the patient's prescription, the user can specify both the maximum number of shots of radiation and a minimum isodose line that must surround the entire treatment volume. After satisfying all of the constraints included in the prescription, the system maximizes the conformity of the dose distribution. This automated approach to treatment planning has been applied retrospectively to a series of patient cases, and each optimized plan has been compared to the corresponding manual plan produced by an experienced user. The results demonstrate that this tool can often improve the tumor dose homogeneity while using fewer shots than were included in the original plan. Therefore, inverse treatment planning should improve both the quality and the efficiency of Gamma Knife treatments.

Algorithms↗

PubMed1994

The FEF25-75% and the clinical diagnosis of asthma.

Nonspecific bronchial provocation testing is clinically useful in the evaluation of patients with symptoms suggestive of asthma. Testing is usually reserved for those with normal or near normal baseline spirometry. Although bronchial provocation testing is safe and widely available, the protocol is time consuming and not without expense. It has been reported that a reduced FEF25-75% in the context of an otherwise normal spirogram suggests that asthma should be considered. To evaluate this suggestion, we compared the baseline FEF25-75% (expressed as percent of predicted) with the results of the subsequent methacholine bronchial provocation test in 205 consecutive patients referred for testing. The mean baseline FEF25-75% in the 112 patients with normally responsive airways (ie, a negative bronchial provocation test) was 95.4 +/- 27.5%. In the 93 patients with a positive bronchial provocation test, the mean FEF25-75% was 77.6 +/- 27.2%. The mean FEF25-75% in those with hyperresponsive airways was significantly lower (t = 4.616, P < .0001). Of those patients with a positive bronchial provocation test, there was no significant correlation, however, between the baseline FEF25-75% and the degree of bronchial hyperresponsiveness as assessed by the PC20FEV1 (r = .154, P = .141). When a significant reduction in FEF25-75% was defined as less than 60% of predicted, the sensitivity of the prediction rule was 25.8%, the specificity was 92.0%, the positive predictive value was 72.7%, and the negative predictive value was 60.0%. From these results, we conclude that the FEF25-75% derived from simple spirometry may be useful in predicting the presence or absence, but not the degree, of bronchial hyperresponsiveness.

Adolescent↗

PubMed1979

Tumour incidence, growth, reproduction and longevity in female C3H mice fed polyunsaturated ruminant-derived foodstuffs.

Earlier studies with the random-bred Quackenbush mouse strain showed that human-type diets based on linoleic acid-enriched foodstuffs derived from ruminants fed protected polyunsaturated oils have no detrimental effects on growth, reproduction or longevity. Tumour incidence and time of onset of tumour development have now been studied in the inbred, tumour-prone mouse strain C3H, in addition to growth, reproduction and longevity. Mice were fed a polyunsaturated human diet, a conventional human diet, or mouse cubes. The results with C3H mice tended to confirm those with Quackenbush strain mice-growth rates and reproductive productivities were very similar in the two groups eating human diets. Mice on the conventional human diet tended to survive better to about 60 weeks of age than mice on the polyunsaturated diet or the cube diet, after which the mortality rates of the mice on the three diets were similar. The degree of unsaturation of the dietary fat had no significant effect on the incidence of tumours. The tumour incidence was about 40% which, taken in conjunction with the average age of onset (about 80 weeks), suggested that the NIV virus rather than the MMTV virus was responsible. It would appear that the high-fat human diets had no effect on the incidence of mammary tumours caused by this virus.

Animal Feed↗

PubMed1979

Growth, reproductive productivity and longevity of mice fed polyunsaturated ruminant-derived foodstuffs.

The effects on the well-being of mice of feeding linoleic acid-enriched foodstuffs derived from ruminants receiving protected polyunsaturated oil were determined. Growth, reproductive productivity and longevity were compared in mice fed freeze-dried human diets containing either these products or the corresponding conventional ruminant-derived foods. A laboratory mouse pellet diet was used as a standard for the comparison. Growth rates and life spans were found to be similar in all three groups. Although the reproductive productivity of the mice on the polyunsaturated diet was never significantly different from that of mice on the conventional human diet, productivities of both groups on human diets were usually significantly below those of mice eating pellets. By the third generation of the second reproduction study, productivities of both these groups of mice had returned to the same level as those of mice eating pellets. Possible reasons for the depression in reproductive productivity in mice on the human diets are discussed. It was concluded that the polyunsaturated human diet neither impaired nor improved the lives of the animals eating the diet relative to the lives of animals eating the conventional human diet.

Adipose Tissue↗