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Biomedical subjects

R G Parker

Publications and source records attributed to R G Parker.

At least 19 recordsLinked to original sources
PubMed2001

High-grade carcinoma of the prostate: a comparison of current local therapies.

OBJECTIVES: To determine the impact of either single or combined local therapeutic modalities for poorly differentiated (Gleason score 8 to 10) prostate cancer. METHODS: Between 1987 and 1996, 156 patients were diagnosed with biopsy proven, poorly differentiated (Gleason score 8 to 10), clinically localized prostate cancer. Of these patients, 87 were treated with radical prostatectomy alone, 19 with radiotherapy, and 24 with both prostatectomy and postoperative radiotherapy. RESULTS: The median follow-up time was 74.6 months. The 5-year biochemical progression-free survival (PFS) for patients with a Gleason score of 8 to 10 was 65%, 30%, and 20% for patients treated with surgery plus postoperative radiotherapy, radiotherapy alone, and surgery alone, respectively (P <0.0001 between postoperative radiotherapy and all other groups, P = 0.6131 between surgery and radiotherapy). The 5-year clinical PFS was 80%, 60%, and 35% for patients treated with surgery plus postoperative radiotherapy, radiotherapy alone, and surgery alone (P <0.0001 between postoperative radiotherapy and all others, P = 0.1975 between surgery and radiotherapy). The independent prognosticators for biochemical failure included serum prostate-specific antigen level greater than 20 ng/mL and seminal vesicle invasion; only seminal vesicle invasion was prognostic for clinical failure. CONCLUSIONS: Patients with high-grade prostate cancer (Gleason score 8 to 10) have uniformly poor, but apparently similar, biochemical and clinical PFS rates when treated by either prostatectomy or radiotherapy alone. The addition of postoperative radiotherapy in the treatment of these patients may be associated with improved biochemical and clinical PFS compared with either modality alone.

Combined Modality Therapy↗
PubMed2001

Radiation oncology: contributions of the United States in the last years of the 20th century.

The advancements in radiation oncology in the past 50 years in the United States were probably more dramatic than those in the first half of the 20th century. Not only were there major technical achievements, but there was also an associated increase in the overall cure rates of cancer, from 20% at 5 years 50 years ago to now nearly 60% at 5 years. The cure rates in selected tumor sites at 5 years in 1950 and in 2000, respectively, were as follows: breast, 50% and 80%; colon and rectum, 40% and 85%; lung, 5% and 15%-20%; prostate, 40% and 80%; Hodgkin disease, 50% and more than 90%; cervix, 40% and 70%-80%; uterus (endometrium), 80% and more than 90%; bladder, 30% and 50%; head and neck, 30% and 60%; and esophagus, 2% and 15%. Much of this has been due to a broader array of techniques in radiation therapy available for treatment but also because of new emphasis on combined integrated modalitities (surgery, radiation therapy, and chemotherapy). New imaging techniques have contributed substantially, allowing better selection of patients for treatment and better selections of treatment modalities.

Combined Modality Therapy↗
PubMed2000

Outcomes and factors impacting local recurrence of ductal carcinoma in situ.

BACKGROUND: The optimal management of ductal carcinoma in situ (DCIS) remains controversial. Investigators have focused on identifying patients who are eligible for treatment by excision alone. A retrospective analysis of patients with DCIS treated by various modalities was conducted to compare outcomes and determine factors significant for local recurrence (LR). METHODS: Between 1985-1992, 88 consecutive diagnoses of DCIS were identified in 85 patients. Seventy-four percent were detected mammographically. The most common histologic subtypes were comedo (54%) and cribriform (23%). Tumor sizes were < 2.5 cm (49%), > 2.5-5 cm (26%), > 5 cm (23%), and unknown (2%). Final resection margins were tumor free (75%), close/positive (23%), and unknown (2%). Treatment methods included mastectomy (30%), localized surgery and radiation therapy (LSR) (43%), or wide localized surgery alone (LS) (27%). Radiation therapy (RT) was comprised of 50 grays to the breast, and 53% of treated patients received local "boost" irradiation. RESULTS: The median follow up was 8.3 years. The overall recurrence rate was 13. 6%, whereas the median time to LR was 27.8 months. Recurrence rates according to treatment modality were: LS: 25%; LSR: 13%; and mastectomy: 4%. However, if surgical margins were tumor free, LSR had a LR rate of 3.4%. After RT, no LR occurred prior to 15 months, and 4 of 5 tumors were noninvasive. Nine patients treated by excision alone conformed to the criteria of Lagios et al. criteria and LR occurred in three of nine tumors. Of the factors analyzed, margin status was found to be the best predictor for LR (P = 0.05). CONCLUSIONS: If surgical margins are tumor free, the LSR regimen is equivalent to mastectomy for local tumor control. Annual mammograms may be adequate for the follow-up of patients with irradiated breasts, but biannual studies still are recommended for patients treated with excision alone.

Adult↗
PubMed2000

Examining the use of breast-conserving treatment for women with breast cancer in a managed care environment.

At a National Institutes of Health Consensus Conference in 1991, conservation treatment was considered preferable for patients with early-stage breast cancer. In the early and mid-1990s, however, less than half of the eligible patients received this treatment and the rates varied with patient and provider characteristics. This study explores whether more eligible patients with breast cancer received conservation treatment in recent years in a managed care environment compared to reports in the literature, and if patient and hospital characteristics affected the rate of acceptance. The study population included 753 women with breast cancer in clinical stages 0, I, or II. Patients with Stage III or IV tumors or with tumors larger that 5.0 cm were excluded. A multiple logistic regression incorporated in a mixed-effect model was used to estimate the effect of patient and facility characteristics on the likelihood of using breast-conserving surgery controlling for clinical stages and demographics such as age, race, and marital status. Among the 753 eligible patients, 474 (62.9%) received conservation surgery. Only Hispanic ethnicity and clinical stage significantly affected the likelihood of receiving conservation treatment. Factors such as patient age, hospital size, and teaching status that had been found to be significant predictors in earlier studies were not statistically significant in this study, although conservation treatment was more frequent in younger women and in teaching hospitals. A larger proportion of eligible patients received conservative treatment in this study than in previous reports. This treatment became available in a broader range of institutions, moving from large, academic teaching centers to smaller community hospitals.

Adult↗
PubMed2000

Structural barriers and facilitators in HIV prevention: a review of international research.

OBJECTIVES: This article provides an overview of a growing body of international research focusing on the structural and environmental factors that shape the spread of the HIV/AIDS epidemic, and create barriers and facilitators in relation to HIV-prevention programs. OVERVIEW OF STRUCTURAL-FACTORS LITERATURE: Most of the research on structural and environmental factors can be grouped into a small number of analytically distinct but interconnected categories: economic (under)development and poverty; mobility, including migration, seasonal work, and social disruption due to war and political instability; and gender inequalities. An additional focus in research on structural and environmental factors has been on the effects of particular governmental and intergovernmental policies in increasing or diminishing HIV vulnerability and transmission. INTERVENTIONS: A smaller subset of the research on structural factors describes and/or evaluates specific interventions in detail. Approaches that have received significant attention include targeted interventions developed for heterosexual women, female commercial sex workers, male truck drivers, and men who have sex with men. CONCLUSIONS: The structural and environmental factors literature offers important insights and reveals a number of productive intervention strategies that might be explored in both resource-rich and -poor settings. However, new methodologies are required to document and evaluate the effects of the structural interventions, which by their very nature involve large-scale elements that cannot be easily controlled by experimental or quasi-experimental research designs. Innovative, interdisciplinary approaches are needed that can move beyond the limited successes of traditional behavioral interventions and explicitly attempt to achieve broader social and structural change.

Developing Countries↗
PubMed1999

Patients with newly diagnosed carcinoma of the breast: validation of a claim-based identification algorithm.

The objectives of this study were to validate a claims-based algorithm for identification of patients with newly diagnosed carcinoma of the breast and to optimize the algorithm. Claims data from all females aged 21 years or older who enrolled in a large California health maintenance organization during the study period from October 1, 1994 through March 31, 1996 were analyzed. Medical records of the patients identified through the claims-based algorithm were reviewed to determine whether the patients were correctly identified. The initial algorithm had a positive predictive value of 84% which was similar to the previous study. The percentages of correct identification significantly increased with the patient's age at diagnosis. Other patient demographic characteristics and facility characteristics were not related to the accuracy of the identification. Using a classification tree procedure and additional information from the false-positive cases, the initial algorithm was modified for improvement. The best-modified algorithm had a positive predictive value of 92% while only 0.5% (4/837) of the true-positive cases were excluded. The results once again demonstrated that patients with newly diagnosed carcinomas of the breast can be identified using claims data. These databases provide an efficient and effective tool for performing health services studies on large patient populations.

Adult↗
PubMed1999

Expression of risk factors for breast cancer in women younger than 49.

The definition of women younger than 49 who are at increased risk for breast cancer would enable intensified efforts in surveillance and use of preventive measures for this group. In this survey of 32,123 members of Health Net, an increased risk for breast cancer was related to age, breast cancer in the immediate family (mother, sister), and previous biopsies for cystic lesions of the breast. No increased risk was related to menarche, nulliparity, first pregnancy after age 30, or breast feeding.

Adult↗
PubMed1998

Axillary node dissection in ductal carcinoma in situ.

Intraductal carcinoma of the breast has become a well-defined entity that has been more frequently diagnosed since the introduction of mammography. For many years, the usual treatment has been mastectomy, often with axillary lymph node dissection. Concurrent with documentation that breast conservation treatment has been effective for many invasive breast cancers, such treatment has been introduced for noninvasive breast cancers (ductal carcinoma in situ and lobular cancer in situ). However, there is no basis for axillary dissection because tumor cells are contained by the basement membrane and should not metastasize. In this study, 107 axillary dissections were carried out, with an average of 20 nodes identified, and a single metastasis was identified.

Breast Neoplasms↗
PubMed1996

Postirradiation sarcoma of the gynecologic tract. A report of 13 cases and a discussion of the risk of radiation-induced gynecologic malignancies.

With improvement in survival after cancer treatment, it is becoming increasingly important to examine treatment-related morbidity and mortality. Sarcomas can develop within the irradiated field after radiation therapy (RT) for gynecologic malignancies. We undertook a study to assess the outcome after treatment of postirradiation sarcoma (PIS) of the gynecologic tract. In reviewing our data and the literature, we compare the absolute risk of PIS and other radiation-associated second malignant neoplasms (SMNs) with the mortality risk of surgery and general anesthesia. Between 1955 and 1987, 114 patients with uterine sarcomas were seen at the University of California, Los Angeles (UCLA), Medical Center. Thirteen had a prior history of RT. Conditions for which these patients received RT included choriocarcinoma (one), menorraghia (four), cervical cancer (six), and ovarian cancer (two). RT doses were known in six cases and ranged from 4,000 to 8,000 cGy. Latency time from RT to the development of PIS ranged from 3 to 30 years, with a median of 17 years. Twelve patients were treated with surgery or additional RT. Two patients remain alive 5 months and 57 months, respectively, following salvage therapy. Five-year disease-specific survival for all patients is 17%. From our data and a review of the literature, we estimate that the absolute risk of PIS with long-term follow-up ranges from 0.03 to 0.8%. Postirradiation sarcoma of the gynecologic tract is a relatively rate event associated with a poor prognosis. Mortality risks of radiation-associated SMN are similar to mortality risks of surgery and general anesthesia. Given the large number of patients with gynecologic malignancies who can be cured or palliated with RT, concern regarding radiation sarcomagenesis should not be a major factor influencing treatment decisions.

Adult↗
PubMed1996

The prognostic value of PSA levels in radiation therapy of patients with carcinoma of the prostate: the UCLA experience 1988-1992.

BACKGROUND AND OBJECTIVES: Pretreatment prostate-specific antigen (PSA) levels may be of prognostic significance for patients with prostate cancer. Posttreatment PSA data are more limited. This study was undertaken to examine the prognostic role of pretreatment and posttreatment PSA levels in the radiation treatment of patients with carcinoma of the prostate. METHODS: One hundred one patients who received primary radiation therapy at UCLA between 1988 and 1992 for clinical stage A to D1 prostate cancer were analyzed. Included were 4 patients with stage A, 77 with stage B, 16 with stage C, and 4 with stage D. All patients had pretherapy and posttherapy PSA values. Patients received definitive radiation therapy with photons (81), neutrons (13), or interstitial implant (7). Correlations were made with other prognostic factors and treatment outcome. RESULTS: Median follow-up was 28 months. At last follow-up, 64% were without evidence of disease, 17% had rising PSA profiles or failure of PSA to normalize (chemical failure), and 19% had local recurrence and/or distant metastases. The 4-year overall survival was 85%, whereas actuarial survival free of chemical or clinical failure was only 32%. Pretreatment PSA levels and posttreatment PSA level normalization at 6 months correlated significantly with disease-free survival. On univariate analysis, pretreatment PSA levels correlated significantly with stage, high versus low Gleason score, and outcome. Posttreatment PSA level normalization at 6 and 12 months correlated with stage, pretreatment PSA level, and outcome, but not with Gleason score. Only PSA level normalization at 6 months and age were independent variables using multivariate analysis. PSA nadir values differed significantly between patients free of disease and those who failed. CONCLUSIONS: In our analysis, posttreatment PSA levels were independently predictive of outcome, whereas pretreatment PSA levels, while correlating with other prognostic factors, were not independently predictive. Given the prognostic value of posttreatment PSA levels, it is appropriate that chemical failures be included in outcome analyses, although this will lower disease-free survival.

Adenocarcinoma↗
PubMed1996

Empowerment, community mobilization and social change in the face of HIV/AIDS.

BACKGROUND: On the basis of recent social and behavioral research, together with more than a decade of practical experience in countries around the world, an important shift has begun to take place in the models or paradigms that have been developed to understand and respond to the HIV/AIDS epidemic. A growing awareness of the complex social, cultural, political and economic forces shaping the epidemic - and, in particular, of the link between the social injustice and increased vulnerability to HIV infection - has led to the reformation of both theory and practice aimed at responding to AIDS and meeting the needs of those most affected by the epidemic. HIV/AIDS PREVENTION: The focus of HIV/AIDS prevention efforts has increasingly shifted from models aimed at changes in individual risk behavior to models aimed at community mobilization. An earlier emphasis on information-based educational campaigns has given way to intervention programs aimed at enablement and empowerment in the face of the epidemic. PERSPECTIVES: These developments have been linked to a new awareness of the fundamental connection between public health and human rights, and to a new understanding of the fight against AIDS as part of a much broader process of social change aimed at redressing structures of inequality, intolerance and injustice.

Community Networks↗
PubMed1995

Biologically effective dose distribution based on the linear quadratic model and its clinical relevance.

PURPOSE: Radiotherapy plans based on physical dose distributions do not necessarily entirely reflect the biological effects under various fractionation schemes. Over the past decade, the linear-quadratic (LQ) model has emerged as a convenient tool to quantify biological effects for radiotherapy. In this work, we set out to construct a mechanism to display biologically oriented dose distribution based on the LQ model. METHODS AND MATERIALS: A computer program that converts a physical dose distribution calculated by a commercially available treatment planning system to a biologically effective dose (BED) distribution has been developed and verified against theoretical calculations. This software accepts a user's input of biological parameters for each structure of interest (linear and quadratic dose-response and repopulation kinetic parameters), as well as treatment scheme factors (number of fractions, fractional dose, and treatment time). It then presents a two-dimensional BED display in conjunction with anatomical structures. Furthermore, to facilitate clinicians' intuitive comparison with conventional fractionation regimen, a conversion of BED to normalized isoeffective dose (NID) is also allowed. RESULTS: Two sample cases serve to illustrate the application of our tool in clinical practice. (a) For an orthogonal wedged pair of x-ray beams treating a maxillary sinus tumor, the biological effect at the ipsilateral mandible can be quantified, thus illustrates the so-called "double-trouble" effects very well. (b) For a typical four-field, evenly weighted prostate treatment using 10 MV x-rays, physical dosimetry predicts a comparable dose at the femoral necks between an alternate two-fields/day and four-fields/day setups. However, our BED display reveals an approximate 21% higher BED for the two-fields/day scheme. This excessive dose to the femoral necks can be eliminated if the treatment is delivered with a 3:2 (anterio-posterior/posterio-anterior (AP/PA): bilaterally opposed (BLO)) dose weighting. With Co-60 beams, the increase of BED with alternate two-fields/day, 1:1 setup was even more pronounced (26%). CONCLUSION: We have demonstrated the feasibility of constructing a biologically oriented dose distribution for clinical practice of radiotherapy. The discordance between physical dose distributions and the biological counterparts based on the given treatment schemes was quantified. The computerized display of BED at nonprescription points greatly enhanced the versatility of this tool. Although the routine use of this implementation in clinical radiotherapy should be cautiously done, depending largely on the accuracy of the published biological parameters, it may, nevertheless, help the clinicians derive an optimal treatment plan with a particular fractionation scheme or use it as a quantitative tool for outcome analysis in clinical research.

Feasibility Studies↗