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Biomedical subjects

R Bissett

Publications and source records attributed to R Bissett.

9 recordsLinked to original sources
PubMed2000

Impact of noninvasive imaging on increased incidental detection of renal cell carcinoma.

OBJECTIVE: To determine the impact of non-invasive imaging, specifically ultrasound imaging and computed tomography, on the incidental detection of renal cell carcinoma during two consecutive time periods, one prior and one subsequent to the acquisition of imaging equipment. METHODS: All located patient charts (83% of 207) of renal cell carcinoma cases (n = 172) were reviewed, and categorized by presentation method as 'incidental' or 'nonincidental' cases, based on defined criteria. Clinical information was recorded, cases were staged, and survival estimates were calculated. RESULTS: More than a third of the 172 cases were categorized as incidentally detected, most of which (82.5%) were detected during the latter time period. Either ultrasound or CT imaging was credited with detecting over 80% of the incidentally detected tumors. CONCLUSION: Ultrasound and CT imaging have contributed to the incidental detection of renal cell carcinomas during the two time periods. Stage significantly predicted survival (p<0.001) in a Cox proportional hazard model that also controlled for presentation, sex, and age.

Carcinoma, Renal Cell↗
PubMed1999

Computer-assisted decision making in portal verification--optimization of the neural network approach.

PURPOSE: Conventional portal verification requires that a qualified radiation oncologist make decisions as to the set-up acceptability. This scheme is no longer sustainable with the large numbers of images available on-line and stringent time constraints. Therefore the objective of this study was to develop, optimize, and evaluate on clinical data an artificial intelligence decision-making tool for portal verification. The tool, based on the artificial neural network (ANN) approach, should approximate, as closely as possible, portal verification assessments made by a radiation oncologist expert. METHODS AND MATERIALS: A total of 328 electronic portal images of tangential breast irradiations were included in the study. A radiation oncologist expert evaluated these images and rated the treatment set-up acceptability on a scale from 0 to 10. Translational and rotational errors in the placement of the radiation field boundaries formed seven-dimensional feature vectors that represented each of the 328 portal images/treatments. The feature vectors were used as inputs to a three-layer, feedforward ANN. The neural network was trained on the oncologist's ratings. RESULTS: The rms discrepancy between the ANN and the expert's ratings was 1.05 rating points. Using the decision threshold equal to 5 for both sets of ratings, the ANN classifier was capable of detecting 100% of the portals classified as "unacceptable" by the expert. Only 6.5% of portals acceptable to the oncologist were misclassified as "unacceptable" by the ANN. CONCLUSION: The results of this study indicate the feasibility of using the ANN portal image classifier as an automated assistant to the radiation oncologist. Its role would be to recommend an appropriate decision as to the acceptability or otherwise of a given treatment set-up depicted in a portal image.

Breast Neoplasms↗
PubMed1999

Application of a fuzzy pattern classifier to decision making in portal verification of radiotherapy.

With the large volume of electronic portal images acquired and stringent time constraints, it is no longer feasible to follow the convention whereby the radiation oncologist reviews and approves or rejects all portals. For that purpose we have developed a portal image classifier based on the fuzzy k-nearest neighbour (k-NN) algorithm. Each portal image is represented by a feature vector that consists of translational and rotational errors in the placement of radiation field borders that were measured in the portal image. Memberships in the acceptable portal class for the reference portal images within a training dataset were defined by a radiation oncologist expert. The fuzzy k-NN portal image classifier was trained and tested on a dataset of 328 portal images acquired during tangential irradiations of the breast. The memberships in the acceptable portal class produced by the fuzzy k-NN algorithm agreed very well with those defined by the expert. The linear correlation coefficient was equal to 0.89. Performance of the fuzzy k-NN classifier was also evaluated from the portal decision-making point of view using the measures of accuracy, sensitivity and specificity. The fuzzy k-NN portal classifier was capable of identifying almost all the truly unacceptable portals with an acceptably low false alarm rate.

Artificial Intelligence↗
PubMed1997

Prostate specific antigen levels during radical radiation therapy and the prediction of outcome in localized carcinoma of the prostate.

There has been substantial interest in the effect of radiation therapy upon serum prostate specific antigen (PSA) levels in patients managed by radiation therapy and their ability to predict the eventual outcome. At our institute, an observational prospective longitudinal study was begun in 1989 to identify prognostic factors for biochemical relapse from among several variables, including PSA levels measured prior to treatment, during treatment, and post-treatment, and to summarize what happens to PSA levels over the course of treatment with radical radiation therapy. A total of 142 patients with adenocarcinoma of the prostate (T1-4, N0, M0) were radically irradiated (6-7 weeks) between February 1989 and January 1991. Serum PSA levels were recorded weekly during radiation therapy in 117 patients. Of these 117, weekly PSA measurements ranged in completeness from 95 to 113 cases. A number of statistical tests were performed on the data with investigative/ exploratory intent. There were 60 biochemical relapses documented in the whole group of 142 patients, with a maximum follow-up of 4.6 years and median follow-up of 3.3 years. Of the candidate prognostic variables tested by univariate analysis, the following emerged as statistically significant (i.e. P < 0.05): each of the four pretreatment factors (absolute PSA value, dichotomous PSA (normal versus above normal), T category and Gleason score); the treatment variables namely, the end-of-treatment PSA, the slope of PSA, and the absolute change in PSA from pretreatment to the end of treatment; and, among post-treatment variables, the first follow-up PSA, the absolute change in PSA from pretreatment to first follow-up, and the return to normal of an above-normal pretreatment PSA by first follow-up. The majority of these factors were then subjected to multivariate Cox proportional hazards (PH) regression analyses. The end-of-treatment PSA and T category were consistently identified as independently statistically significant factors associated with biochemical relapse. The Gleason score was selected less consistently, and never when defined on a categorical scale. Therefore, using a Cox PH model with the variables of end-of-treatment PSA and T category, both defined on a categorical scale, we developed three prognostic groups with good, intermediate and poor prognoses (chi 2 TREND = 40.7; P < 0.0001). Their 3-year biochemical relapse-free rates, for example, were: 91%, (standard error (SE) 5%); 64% (SE 9%); and 24% (SE 6%), respectively. However, substitution of the baseline value of PSA, which was also strongly associated with outcome, and using the data from all 142 patients, provided similarly distinct prognostic groups (chi 2 TREND = 41.6; P < 0.0001), with corresponding 3-year relapse-free rates of: 92% (SE 4%); 79% (SE 7%); and 30% (SE 6%). Mean weekly PSA levels measured during treatment were found to have a negatively sloping or decreasing tendency. A statistically significant decrease in PSA occurred from pretreatment to the end of treatment (t116 = 7.5; P < 0.0001); the geometric mean of the ratio of end-of-treatment PSA to PSA at pretreatment was 0.7 (95% CI 0.6-0.8). The end-of-treatment PSA and T category emerged as independently statistically significant prognostic variables predicting biochemical relapse. Using the fitted Cox PH model with these two variables, three distinct prognostic groups were identified. The results using pretreatment PSA instead of end-of-treatment PSA produced similarly distinct prognostic groups. Mean weekly PSA levels measured during treatment exhibited a decreasing tendency, and a statistically significant decrease in PSa from pretreatment to the end of treatment was observed.

Adenocarcinoma↗
PubMed1996

Quantitative vs. subjective portal verification using digital portal images.

PURPOSE: Off-line, computer-aided prescription (simulator) and treatment (portal) image registration using chamfer matching has been implemented on PC based viewing station. The purposes of this study were (a) to evaluate the performance of interactive anatomy and field edge extraction and subsequent registration, and (b) to compare observer's perceptions of field accuracy with measured discrepancies following anatomical registration. METHODS AND MATERIALS: Prescription-treatment image pairs for 48 different patients were examined in this study. Digital prescription images were produced with the aid of a television camera and a digital frame grabber, while the treatment images were obtained directly from an on-line portal imaging system. To facilitate perception of low contrast anatomical detail, on-line portal images were enhanced with selective adaptive histogram equalization prior to extraction of anatomical edges. Following interactive extraction of anatomical and field border information by an experienced observer, the identified anatomy was registered using chamfer matching. The degree of conformity between the prescription and treatment fields was quantified using several parameters, which included relative prescription field coverage and overcoverage, as well as the translational and rotational displacements as measured by chamfer matching applied to the boundaries of the two fields. These quantitative measures were compared with subjective evaluations made by four radiation oncologists. RESULTS: All the images in this series that included a range of the most commonly seen treatment sites were registered and the conformity parameters were found. The mean treatment/prescription field coverage and overcoverage were approximately 95 and 7%, respectively before registration. The mean translational displacement in the transverse and cranio-caudal directions were 2.9 and 3.4 mm, respectively. The mean rotational displacement was approximately 2 degrees. For all four oncologists, the portals classified as unacceptable, in terms of the field placement, exhibited significantly higher (p < 0.03) translational errors in the transverse direction. The field coverages were significantly lower (p < 0.05) and the translational errors in the cranio-caudal direction were significantly higher (p < 0.05) for the portals rated as unacceptable by two of the oncologists. CONCLUSIONS: From the parameters that were used to quantify the degree of conformity between the prescription and treatment fields, the translational error in the transverse direction correlated best with the oncologists' assessments on the field placement. Field coverage and translational error in the cranio-caudal direction correlated well with assessments of only two out of the four participating oncologists. This can be explained by the fact that for the majority of treatment sites included in the study the positioning of field borders was more critical for the transverse direction. A conclusion for the design of future quantitative and automated on-line portal verification systems is that they will have to model different perceived significances of different types of localization errors intrinsic to oncologist evaluation of portal images.

Algorithms↗
PubMed1995

Radiotherapy portal verification: an observer study.

In many radiotherapy facilities radiotherapy portal verification is currently a subjective process based on the visual comparison of a treatment or portal image with a prescription or simulation image. The reliability of this process is unknown. We describe here a study in which 16 observers (oncologists, physicists and therapists) independently evaluated the geometric accuracy of 530 treatment fields on 45 patients. The treatment images were acquired by the BEAMVIEW on-line portal imaging system (Siemens Medical Laboratories, Concord, CA, USA). Illustrative examples of the large variation in observers' assessments of the same field are given. The kappa statistic is used to evaluate the degree of agreement between observers and between on-line (at the treatment unit) and off-line (in a quiet viewing room) assessments. The best interobserver agreement was between the four oncologists contributing to the study although this level of agreement was rated only as "fair". Comparison of on-line and off-line decisions made by therapists exhibited "poor" agreement. This study has provided statistical confirmation of the suspicions of many workers in the field of radiotherapy portal verification, viz that the subjective evaluation of field accuracy is unreliable. However, the degree of unreliability is surprisingly large. The inconsistencies between observers documented in this study need to be clearly acknowledged in the development of protocols for the clinical use of on-line portal imaging systems. Acceptable reliability in radiotherapy portal verification will only be achieved when subjective decision making is eliminated.

Humans↗
PubMed1993

The results of primary radiation therapy in the management of squamous cell carcinoma of the penis.

PURPOSE: The outcome of radical external beam radiation therapy for 26 consecutive patients with invasive carcinoma of the penis treated between 1970 and 1985 was assessed to test the efficacy, and side effects of such treatment. METHODS AND MATERIAL: A retrospective review of 26 patients with invasive carcinoma of the penis and 11 patients with carcinoma in-situ of the penis, treated at the Princess Margaret Hospital between 1970 and 1985, was performed. Radiation treatment was delivered using 60Co or 100-250 kv equipment to a dose ranging from 25 Gy in 10 fractions over 2 weeks to 60 Gy in 25 fractions over 5 weeks. The most often used XRT prescription was 50 Gy in 20 fractions over 4 weeks. RESULTS: The 5-year overall actuarial survival for patients with invasive cancers was 62% (+/- 10) and the cause-specific survival was 69% (+/- 9). The control of the primary lesion was 61.5%. Of five patients who progressed after initial radiotherapy, one patient was salvaged by penectomy. Of 11 patients who recurred after initial complete response, three did so in the penis alone and all were successfully salvaged by penectomy. Late complications were recorded in seven patients, two of whom underwent penectomy as a result. All patients with carcinoma in-situ achieved a complete response and, with follow-up ranging from 1 to 14 years, none recurred. CONCLUSION: We conclude that radiation therapy with surgery reserved for the management of local recurrence is an effective first line treatment for patients with carcinoma of the penis.

Actuarial Analysis↗
PubMed1988

"Ratio" and "difference" judgments for length, area, and volume: are there two classes of sensory continua?

Subjects were required to judge ratios and differences of (a) line length for pairs of lines, (b) area for pairs of squares, and (c) volume for pairs of cubes. Nonmetric analyses of these judgments indicated that all subjects were able to make consistent ratio judgments for all three continua. Many of the subjects, when asked to judge subjective differences, however, performed as if they were judging subjective ratios rather than differences. The data for the few subjects who appeared to be judging subjective differences were not consistent across subjects and conditions. Previous studies of ratio and difference judgments of loudness and heaviness, on the other hand, showed the opposite pattern, in that subjects most often behaved as if they were judging sensory differences when asked to judge sensory ratios. We propose that ratio judgments are more natural to perceptual continua along which stimuli are easily "decomposed" into a number of smaller perceptual units.

Attention↗