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R Cormack

Publications and source records attributed to R Cormack.

16 recordsLinked to original sources
PubMed2001

Intraoperative planning and evaluation of permanent prostate brachytherapy: report of the American Brachytherapy Society.

PURPOSE: The preplanned technique used for permanent prostate brachytherapy has limitations that may be overcome by intraoperative planning. The goal of the American Brachytherapy Society (ABS) project was to assess the current intraoperative planning process and explore the potential for improvement in intraoperative treatment planning (ITP). METHODS AND MATERIALS: Members of the ABS with expertise in ITP performed a literature review, reviewed their clinical experience with ITP, and explored the potential for improving the technique. RESULTS: The ABS proposes the following terminology in regard to prostate planning process: *Preplanning--Creation of a plan a few days or weeks before the implant procedure. *Intraoperative planning--Treatment planning in the operating room (OR): the patient and transrectal ultrasound probe are not moved between the volume study and the seed insertion procedure. * Intraoperative preplanning--Creation of a plan in the OR just before the implant procedure, with immediate execution of the plan. *Interactive planning--Stepwise refinement of the treatment plan using computerized dose calculations derived from image-based needle position feedback. *Dynamic dose calculation--Constant updating of dose distribution calculations using continuous deposited seed position feedback. Both intraoperative preplanning and interactive planning are currently feasible and commercially available and may help to overcome many of the limitations of the preplanning technique. Dosimetric feedback based on imaged needle positions can be used to modify the ITP. However, the dynamic changes in prostate size and shape and in seed position that occur during the implant are not yet quantifiable with current technology, and ITP does not obviate the need for postimplant dosimetric analysis. The major current limitation of ITP is the inability to localize the seeds in relation to the prostate. Dynamic dose calculation can become a reality once these issues are solved. Future advances can be expected in methods of enhancing seed identification, in imaging techniques, and in the development of better source delivery systems. Additionally, ITP should be correlated with outcome studies, using dosimetric, toxicity, and efficacy endpoints. CONCLUSION: ITP addresses many of the limitations of current permanent prostate brachytherapy and has some advantages over the preplanned technique. Further technologic advancement will be needed to achieve dynamic real-time calculation of dose distribution from implanted sources, with constant updating to allow modification of subsequent seed placement and consistent, ideal dose distribution within the target volume.

Brachytherapy↗
PubMed2000

Identifying the predictors of acute urinary retention following magnetic-resonance-guided prostate brachytherapy.

PURPOSE: Larger prostate gland volumes have been associated with long-term urinary morbidity in prostate interstitial radiation therapy utilizing ultrasound image guidance technique. This study was performed to identify the clinical and technical predictors of acute urinary retention following magnetic-resonance (MR)-guided prostate interstitial brachytherapy. METHODS AND MATERIALS: Fifty patients underwent MR-guided prostate brachytherapy between December 1997 and March 1999. Patient selection was limited to men with stage T1cNXM0 disease, PSA of less than10 ng/mL, biopsy Gleason score not more than 3 + 4, and endorectal coil MR stage T2 disease. Dosimetry plans were developed in the operating room and (125)Iodine sources were implanted using MR real-time guidance. The peripheral zone (PZ) of the prostate gland was defined as the clinical target volume (CTV) and the minimum prescribed dose to the CTV was 137 Gy. The volumes of the PZ, transition zone (TZ), and total prostate gland volume were also determined by MR. Individual source strength ranged from 0.35 to 0.54 microGym(2)/h (NIST 99, median 0.46 microGym(2)/h) and the total implanted activity ranged from 17.0 to 43.1 mCi (median, 28.1 mCi) using 43-120 seeds (median, 79). The seeds were placed using MR-compatible biopsy needles (14-28, median, 19). RESULTS: The ability of clinical (MR defined prostate, PZ, and TZ volumes) and technical (number of catheters, number of seeds implanted, and total activity) factors to predict AUR for 50 men undergoing MR-guided prostate interstitial brachytherapy were evaluated using univariable and logistic regression multivariable analyses. Six men (12%) experienced AUR within 24 h after removal of the Foley catheter subsequent to prostate brachytherapy. The total number of seeds (p = 0.05), MR determined prostate volume (p < 0.01), and the MR-determined TZ volume (p < 0.01) were significant predictors of AUR on univariable analysis. Utilizing a multivariable logistic regression analysis, the TZ volume was the only significant predictor of AUR (p < 0.01). The prostate volume is highly correlated to the TZ volume (Spearman correlation coefficient of 0. 91) and was thus significant in the univariable analysis; however, the prostate volume did not add prognostic value in multivariable analysis. CONCLUSION: Benign prostatic hyperplasia (BPH) resulting in an enlarged TZ volume, is the most important predictor of AUR following MR-guided prostate interstitial radiation therapy. Although AUR was significant (60%) in men with moderate BPH (TZ volume >/= 50 cc), it was also self-limiting.

Analysis of Variance↗
PubMed2000

Real-time magnetic resonance imaging-guided brachytherapy in the treatment of selected patients with clinically localized prostate cancer.

BACKGROUND AND PURPOSE: A real-time three-dimensional magnetic resonance imaging (MRI)-guided implant technique has been designed and implemented. This report summarizes the dosimetry achieved and the acute morbidity in the first patients. PATIENTS AND METHODS: To date, 43 patients with clinical stage T(1c)N(X)M(0) prostate cancer, serum prostate specific antigen <10 ng/mL, and biopsy Gleason score no higher than 3 + 4 have been treated. The procedure was performed using an open magnet, with axial T1-weighted and fast spin echo images. The prescribed minimum radiation dose to the peripheral zone was 160 Gy. The total activity implanted ranged from 18.8 to 47.5 mCi using 43 to 120 (median 80) (125)I seeds. Dosimetric analyses were performed intraoperatively in real time for the tumor, anterior rectal wall, and prostatic urethra. RESULTS: The percent of the clinical target volume receiving the prescription dose was 89% to 99% (median 96%). Using a conservative estimate of 164 Gy, no more than 9% of the urethral volume exceeded the tolerated dose. Using an estimated tolerated dose of 82 Gy, 30% to 100% (median 68%) of the anterior rectal wall volume was within the dose limit. Thirty-nine patients voided spontaneously within 3 hours of Foley catheter discontinuation, although four patients required recatheterization for a period. No patient reported gastrointestinal or sexual dysfunction during the first postoperative month. CONCLUSION: A real-time MR-guided technique can achieve a minimum of 89% coverage of the tumor volume while maintaining the prostatic urethra and most of the anterior rectal wall below tolerance levels. Acute morbidity was minimal. Further follow-up is needed to ascertain the impact on cancer control and quality of life.

Aged↗
PubMed2000

Three-dimensional real-time magnetic resonance-guided interstitial prostate brachytherapy optimizes radiation dose distribution resulting in a favorable acute side effect profile in patients with clinically localized prostate cancer.

PURPOSE: A large number of men are diagnosed with early-stage prostate cancer as a result of prostate-specific antigen (PSA) screening. For many of these men, prostatectomy results in long-term freedom from biochemical and clinical failure. Despite limited follow-up data, ultrasound-guided prostate brachytherapy has gained acceptance as a treatment for early-stage prostate cancer, in part due to its favorable side effect profile and brief recovery period. We report on the use of three-dimensional real-time magnetic resonance (MR) guidance, which has several advantages compared with biplanar ultrasound guidance for prostate brachytherapy, including enhanced geometric and dosimetric feedback during the procedure. MATERIALS AND METHODS: Median clinical target volume coverage of 96% was achieved using MR guidance. The ability to define more precisely the clinical target volume with MR and the use of real-time assessment of dose distribution resulted in an excellent acute side effect profile. Only 19% of patients required oral alpha1 blockers for postimplant urethritis and 9% required temporary reinsertion of the Foley catheter due to acute urinary obstruction. CONCLUSIONS: These results compare favorably to those of ultrasound-guided brachytherapy. Further follow-up is needed to ascertain the impact this technique will have on cancer control and long-term quality of life.

Aged↗
PubMed2000

Transperineal magnetic resonance image guided prostate biopsy.

PURPOSE: We report the findings of a transperineal magnetic resonance image (MRI) guided biopsy of the prostate in a man with increasing prostate specific antigen who was not a candidate for a transrectal ultrasound guided biopsy. MATERIALS AND METHODS: Using an open configuration 0.5 Tesla MRI scanner and pelvic coil, a random sextant sample was obtained under real time MRI guidance from the peripheral zone of the prostate gland as well as a single core from each MRI defined lesion. The patient had previously undergone proctocolectomy for ulcerative colitis and, therefore, was not a candidate for transrectal ultrasound guided biopsy. Prior attempts to make the diagnosis of prostate cancer using a transurethral approach were unsuccessful. RESULTS: The random sextant samples contained benign prostatic hyperplasia, whereas Gleason grade 3 + 3 = 6 adenocarcinoma was confirmed in 15% and 25% of the 2 cores obtained from the MRI targeted specimens of 2 defined lesions. The procedure was well tolerated by the patient. CONCLUSIONS: Transperineal MRI guided biopsy is a new technique that may be useful in detecting prostate cancer in men with increasing prostate specific antigen who are not candidates for transrectal ultrasound guided biopsy.

Adenocarcinoma↗
PubMed1998

Real-time magnetic resonance image-guided interstitial brachytherapy in the treatment of select patients with clinically localized prostate cancer.

PURPOSE: This study was performed to establish the dose-localization capability and acute toxicity of a real-time intraoperative magnetic resonance (MR) image-guided approach to prostate brachytherapy in select patients with clinically localized prostate cancer. METHODS AND MATERIALS: Nine patients with 1997 American Joint Commission on Cancer (AJCC) clinical stage T1cNxM0 prostate cancer, prostate-specific antigen (PSA) < 10 ng/ml, biopsy Gleason score not exceeding 3 + 4, and endorectal coil MR stage T2 disease were enrolled into this study. The prescribed minimum peripheral dose was 160 Gy to the clinical target volume (CTV), which was the MR-defined peripheral zone (PZ) of the prostate gland. Using a real-time 0.5 Tesla intraoperative MR imaging unit, 5-mm image planes were obtained throughout the prostate gland. The PZ of the prostate gland, anterior rectal wall, and prostatic urethra were identified on the T2 weighted axial images by an MR radiologist. An optimized treatment plan for catheter insertion was generated intraoperatively. Each catheter containing the 125Iodine sources was placed under real-time MR guidance to ensure that its position in the coronal, sagittal, and axial planes was in agreement with the planned trajectory. Real-time dose- volume histogram analyses were used intraoperatively to optimize the dosimetry. RESULTS: For the 9 study patients, 89-99% (median 94%) of the CTV received a minimum peripheral dose of 160 Gy and > or = 95% of the volume of the prostatic urethra and 42-89% (median 70%) of the volume of the anterior rectal wall received doses that were below the reported tolerance. All patients voided spontaneously within 3 h after discontinuation of the Foley catheter and no patient required more than a limited course (< or = 3 weeks) of oral alpha-1 blockers for postimplant urethritis. CONCLUSIONS: Real-time MR-guided interstitial radiation therapy provided the ability to achieve the planned optimized dose-volume histogram profiles to the CTV and healthy juxtaposed structures intraoperatively, with minimal acute morbidity.

Aged↗
PubMed1993

Estimating the population prevalence of injection drug use and infection with human immunodeficiency virus among injection drug users in Glasgow, Scotland.

Although data on the prevalence of injection drug use are an essential prerequisite for estimating the number of individuals infected with the human immunodeficiency virus (HIV), there have been few attempts to utilize statistical methods of population estimation based on multiple data sources. Data on 3,670 cases (2,866 individuals) were obtained from the HIV test register, drug treatment agencies, police records, and needle and syringe exchanges in Glasgow, Scotland, in 1990. Log-linear analysis was used to model the number of individuals in each of the sources. The model incorporating dependency among the three health care agencies (HIV test, drug treatment, and needle exchange) and independence of the police sample fitted the data well, with a residual chi 2 value of 2.9 (6 df). The expected value of the missing cell corresponding to absence from all four samples was 5,628, yielding an overall estimate of 8,494 injectors (95% confidence interval (CI) 7,491-9,721), for a prevalence rate of 1.35% for people aged 15-55 years in Glasgow during 1990. The high ratio of known to unknown injectors (1:2) resulted from the extensive coverage of known injectors and the relatively high level of overlap between the combined health care agency sample and the police sample. While further analysis demonstrated that the probability of appearing in the four samples varied by age and sex, heterogeneity in the population did not affect the choice of model or substantially alter the estimates for the total number of unknown injectors. A concurrent study of a community-wide sample of 503 injectors resulted in an HIV prevalence rate of 1.1% (95% CI 0.4-2.5%). The results of these studies were combined to produce a further estimate of 93 HIV-infected current injectors in Glasgow (95% CI 33-214).

Adolescent↗
PubMed1992

Misdirected visual motion in the peripheral visual field.

An object moving against a textured background is accurately perceived when viewed foveally, but when viewed peripherally the object's perceived direction of motion may deviate from veridical by as much as 90 deg. The illusory direction is oblique to the orientation of the background contours, which may themselves be moving or stationary. In several experiments, we examined the boundary conditions for occurrence of the illusion and tested hypotheses concerning its basis. This illusion of perceived direction dramatizes differences in motion processing between the fovea and the periphery.

Fixation, Ocular↗
PubMed1991

Discrepancy between the short and long term effects of ouabain on the sodium pumps of human cells grown in culture.

1. Human cells (HeLa) were cultured for periods up to 48 h in growth medium in the absence or presence of a range of concentrations of cardiac glycosides. In some experiments the potassium concentration of the medium was varied between 0.3 mM and the usual 5 mM. 2. For periods up to 2 h in ouabain the association and dissociation rate constants were measured and the equilibrium binding constant (KD) calculated; the apparent equilibrium binding constant (K'D) was measured after 1-2 days growth in ouabain. 3. Ouabain had a K'D after 2 days of 2-6 nM in 5 mM K+ growth medium, a 4 fold greater blocking effect on sodium pumps after 2 days than expected from the association and dissociation rate constants measured in untreated or previously ouabain-treated cells. 4. This effect was: (a) approximately the same over a range of external potassium concentrations from 0.3 to 5 mM, although the absolute effect of ouabain over this range of potassium was much different; (b) probably not due to different isoforms of pumps in cells grown in ouabain compared to untreated cells; (c) apparently not a consequence of internalisation of pump-glycoside complexes. 5. We conclude that ouabain has only a limited access to sodium pumps in whole cells; this could be because sodium pumps cycle continuously through an inaccessible region of the plasma membrane. This effect needs to be considered both in the assessment of the magnitude of the long term effects of cardiac glycosides on cells, and in the measurement of the glycoside affinities of various isoforms of the pump.

Cardiac Glycosides↗