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Biomedical subjects

K Mah

Publications and source records attributed to K Mah.

At least 19 recordsLinked to original sources
PubMed2001

Observer variation in contouring gross tumor volume in patients with poorly defined non-small-cell lung tumors on CT: the impact of 18FDG-hybrid PET fusion.

PURPOSE: To quantify interobserver variation in gross tumor volume (GTV) localization using CT images for patients with non-small-cell lung carcinoma and poorly defined tumors on CT and to determine whether variability would be reduced if coregistered 2-[18F]fluoro-2-deoxy-d-glucose (FDG)-hybrid positron emission tomography (PET) with CT images were used. METHODS AND MATERIALS: Prospectively, 30 patients with non-small-cell lung carcinoma had CT and FDG-hybrid PET examinations in radiation treatment position on the same day. Images were coregistered using eight fiducial markers. Guidelines were established for contouring GTVs. Three radiation oncologists performed localization independently. The coefficient of variation was used to assess interobserver variability. RESULTS: The size of the GTV defined showed great variation among observers. The mean ratios of largest to smallest GTV were 2.31 and 1.56 for CT only and for CT/FDG coregistered data, respectively. The addition of PET reduced this ratio in 23 of 30 cases and increased it in 7. The mean coefficient of variation for GTV based on the combined modalities was significantly smaller (p < 0.01) than that for CT data only. CONCLUSIONS: High observer variability in CT-based definition of the GTV can occur. A more consistent definition of the GTV can often be obtained if coregistered FDG-hybrid PET images are used.

Adult↗
PubMed2001

The nature of human orgasm: a critical review of major trends.

This critical review presents a synthesis of the available theoretical and empirical literatures on human orgasm. Findings from both normal and clinical human populations are included. Two major trends in the literature, the dichotomization of biological and psychological perspectives and the assumption of gender differences, are highlighted. A new multidimensional model of the psychological experience of orgasm is described with a view to futhering a biopsychological approach applicable to both sexes. Clinical applications of this new model are discussed.

Female↗
PubMed2001

Decreased bone mineral density is common after autologous blood or marrow transplantation.

Survivors of autologous blood or marrow transplantation (ABMT) are predisposed to decreased bone mineral density (BMD), but data are lacking on the incidence and risk factors for this condition. Therefore, we measured BMD in 64 of 68 consecutive ABMT survivors (35 men and 29 women) attending the University of Toronto ABMT long-term follow-up clinic. Patients were evaluated a median of 4.2 years (range: 4.9 months-11.4 years) after ABMT. Median age at evaluation was 49.6 years (range: 23.5-68.2 years). At the L1-L4 vertebrae, 17 (26%) patients (eight men and nine women) had osteopenia and one male (2%) had osteoporosis. Mean BMD at L1-L4 did not differ from healthy young adults or age and sex matched controls. At the femoral neck, 30 patients (46%) (18 men and 12 women) had osteopenia and five (8%) (two men and three women) had osteoporosis. Mean BMD at the femoral neck was significantly lower than in healthy young adults and age- and sex-matched controls. By regression analysis, patients with decreased BMD were older than those with normal BMD (P = 0.02). Gender, body mass index, time from BMT to evaluation and presence of hypogonadism were not associated with decreased BMD. Treatment of decreased bone density was instituted and follow-up data were obtained 1 year after treatment in 22 of 39 patients with reduced BMD. Nineteen (86%) patients had stabilization or improvement of their bone density at follow-up. We conclude that, after ABMT, over half of the patients have evidence of osteopenia or osteoporosis. Men and women were equally affected. In our study, only older age at evaluation was predictive for loss of BMD. We recommend the measurement of BMD as an integral component to the follow-up of ABMT patients.

Adult↗
PubMed1998

Target position variability throughout prostate radiotherapy.

PURPOSE: To quantify the variability in prostate and seminal vesicle position during a course of external beam radiotherapy, and to measure the proportion of target variability due to setup error. METHODS AND MATERIALS: Forty-four weekly planning computerized tomography (CT) studies were obtained on six patients undergoing radiotherapy for prostate cancer. All patients were scanned in the radiotherapy treatment position, supine with an empty bladder, with no immobilization device. All organs were outlined on 3-mm-thick axial CT images. Anterior and lateral beam's eye view digitally reconstructed radiographs and multiplanar reformatted images were generated. The position of the prostate and seminal vesicles relative to the isocenter location as set that day was recorded for each CT study. Target position relative to a bony landmark was measured to determine the relative contribution of setup error to the target position variability. RESULTS: The seminal vesicle and prostate position variability was most significant in the anterior-posterior (AP) direction, followed by cranial-caudal (CC) and mediolateral (ML) directions. Setup error contributed significantly to the total target position variability. Rectal filling was associated with a trend to anterior movement of the prostate, whereas bladder filling was not associated with any trends. Although most deviations from the target position determined at the initial planning CT scan were within 10 mm, deviations as large as 15 mm and 19 mm were seen in the prostate and seminal vesicles respectively. Target position variations were evenly distributed around the initial target position for some patient studies, but unpredictable patterns were also seen. From a simulation based on the observed variability in target position, the AP, CC, and ML planning target volume (PTV) borders around the clinical target volume (CTV) required for target coverage with 95% certainty are 12.4 mm, 10.3 mm, and 5.6 mm respectively for the prostate and 13.8 mm, 8.6 mm, and 3.9 mm respectively for the seminal vesicles. CONCLUSION: Target position variability is significant during prostate radiotherapy, requiring large PTV borders around the CTV. This target position variability may be potentially reduced by improving the setup accuracy.

Humans↗
PubMed1998

Computed tomographic simulation of craniospinal fields in pediatric patients: improved treatment accuracy and patient comfort.

PURPOSE: To reduce the time required for planning and simulating craniospinal fields through the use of a computed tomography (CT) simulator and virtual simulation, and to improve the accuracy of field and shielding placement. METHODS AND MATERIALS: A CT simulation planning technique was developed. Localization of critical anatomic features such as the eyes, cribriform plate region, and caudal extent of the thecal sac are enhanced by this technique. Over a 2-month period, nine consecutive pediatric patients were simulated and planned for craniospinal irradiation. Four patients underwent both conventional simulation and CT simulation. Five were planned using CT simulation only. The accuracy of CT simulation was assessed by comparing digitally reconstructed radiographs (DRRs) to portal films for all patients and to conventional simulation films as well in the first four patients. RESULTS: Time spent by patients in the CT simulation suite was 20 min on average and 40 min maximally for those who were noncompliant. Image acquisition time was <10 min in all cases. In the absence of the patient, virtual simulation of all fields took 20 min. The DRRs were in agreement with portal and/or simulation films to within 5 mm in five of the eight cases. Discrepancies of > or =5 mm in the positioning of the inferior border of the cranial fields in the first three patients were due to a systematic error in CT scan acquisition and marker contouring which was corrected by modifying the technique after the fourth patient. In one patient, the facial shield had to be moved 0.75 cm inferiorly owing to an error in shield construction. CONCLUSIONS: Our analysis showed that CT simulation of craniospinal fields was accurate. It resulted in a significant reduction in the time the patient must be immobilized during the planning process. This technique can improve accuracy in field placement and shielding by using three-dimensional CT-aided localization of critical and target structures. Overall, it has improved staff efficiency and resource utilization.

Adolescent↗
PubMed1996

Home safe home.

Explore the source record for details and available documents.

Accidents, Home↗
PubMed1994

Genetics of a pheromonal difference contributing to reproductive isolation in Drosophila.

Although sexual isolation is one of the most important causes of speciation, its genetic basis is largely unknown. Here evidence is presented that suggests that sexual isolation between two closely related species of Drosophila is largely caused by differences in female cuticular hydrocarbons. This difference maps to only one of the three major chromosomes, implying that reproductive isolation might have a fairly simple genetic basis. The effect of the hydrocarbons on courtship may help explain the ubiquitous asymmetry of sexual isolation between many pairs of Drosophila species.

Animals↗
PubMed1994

Quantitative effect of combined chemotherapy and fractionated radiotherapy on the incidence of radiation-induced lung damage: a prospective clinical study.

PURPOSE: The objective of this work was to assess the incidence of radiological changes compatible with radiation-induced lung damage as determined by computed tomography (CT), and subsequently calculate the dose effect factors (DEF) for specified chemotherapeutic regimens. METHODS AND MATERIALS: A prospective, clinical study was conducted to determine the response of normal lung tissue to combined chemotherapy and radiotherapy. Radiation treatments were administered once daily, 5 days-per-week. Six clinical protocols were evaluated: ABVD (adriamycin, bleomycin, vincristine, and DTIC) followed by 35 Gy in 20 fractions; MOPP (nitrogen mustard, vincristine, procarbazine, and prednisone) followed by 35 Gy in 20; MOPP/ABVD followed by 35 Gy in 20; CAV (cyclophosphamide, adriamycin, and vincristine) followed by 25 Gy in 10; and 5-FU (5-fluorouracil) concurrent with either 50-52 Gy in 20-21 or 30-36 Gy in 10-15 fractions. CT examinations were taken before and at predetermined intervals following radiotherapy. CT evidence for the development of radiation-induced damage was defined as an increase in lung density within the irradiated volume. The radiation dose to lung was calculated using a CT-based algorithm to account for tissue inhomogeneities. Different fractionation schedules were converted using two isoeffect models, the estimated single dose (ED) and the normalized total dose (NTD). RESULTS: A total of 102 patients were entered and 70 completed the study. Forty-two patients developed CT changes compatible with lung damage. The actuarial incidence of radiological pneumonitis was 71% for the ABVD, 49% for MOPP, 52% for MOPP/ABVD, 67% for CAV, 73% for 5-FU radical, and 58% for 5-FU palliative protocols. Depending on the isoeffect model selected and the method of analysis, the DEF was 1.11-1.14 for the ABVD, 0.96-0.97 for the MOPP, 0.96-1.02 for the MOPP/ABVD, 1.03-1.10 for the CAV, 0.74-0.79 for the 5-FU radical, and 0.94 for the 5-FU palliative protocols. CONCLUSION: Quantitative dose effect factors (DEF) were measured by comparing the incidences of CT-observed lung damage in patients receiving chemotherapy and radiotherapy to those receiving radiotherapy alone. The addition of ABVD or CAV appeared to reduce the tolerance of lung to radiation.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

Sexuality and end-stage renal disease: research and clinical recommendations.

Available studies of sexuality in end-stage renal disease (ESRD) patients are critically reviewed under three headings: (1) descriptive studies of dialysis patients, (2) intervention studies with dialysis patients, and (3) descriptive studies of renal transplant recipients. These studies suggest the presence of significant sexual deficits in uremic (predialysis) and dialysis patients that are only partially alleviated by transplantation or other medical interventions. There are no systematic evaluations of nonmedical interventions for sexual problems in ESRD patients. Most of the research has adopted a reductionist model of sexual behavior and suffers from poor methodology, unstandardized and incomplete measurement of sexual behavior, limited sample sizes, unrepresentative populations, an overemphasis on erectile problems, and a lack of attention to female sexuality. A holistic, biopsychosocial approach is recommended to guide further research and clinical work in this area.

Adult↗
PubMed1994

Learning about sex outside the gutter: attitudes toward a computer sex-expert system.

In an ongoing research program investigating the utility of Sexpert, an expert computer system designed to counsel couples about their sexual relationships, we tested whether sexually active couples' attitudes concerning computerized sexual counseling could be affected by interacting with Sexpert. Eighty-one young heterosexual couples drawn from the university and general community were assigned to one of three sources of feedback about couple sexual functioning (Sexpert, a video, a self-help book) or a control condition. Attitudes toward all counseling sources used in the study were assessed through semantic differential and similarity-dissimilarity questionnaires. Subjects in the Sexpert condition showed significant improvements in their attitudes toward computerized sexual counseling and evaluated Sexpert significantly better and more similar to a human therapist as a result of exposure. Subjects in the other three conditions showed no significant changes in attitudes. This study provides strong evidence for the acceptability of a computerized sex-expert system.

Adolescent↗
PubMed1991

On the impact of tissue inhomogeneity corrections in clinical thoracic radiation therapy.

The magnitude and impact of the corrections required for calculated absorbed doses due to the presence of real anatomic inhomogeneities were studied in 100 "standard" clinical thoracic cases. Correction factor distributions were generated with the equivalent tissue-air ratio method. The correction factors at the point of target absorbed dose, the average within the high dose area, and the average and maximum within the irradiated lung tissue were determined. Results indicate that among patients undergoing similar treatment techniques and radiation energy, correction factors can vary greatly. The diversity in anatomy, geometry, and density emphasizes the need for patient-specific dose calculations if the appropriate accuracy is to be achieved. Even for simple parallel-opposed fields encompassing the mediastinal and bilateral lung regions, the correction at the point of target absorbed dose was found to be as much as 5 to 16% for photon energies between 60Co and 25 MV. The average correction factor within the high dose region was generally comparable in value. For beams that traverse the lungs obliquely, the correction factor at the point of target absorbed dose was as large as 1.21 with 25 MV photons. These values correlated linearly with the lung pathlength preceding the point. Within lung tissues, the corrections were often more dramatic. Using the dose response curve for normal lung tolerance, the clinical consequence of ignoring the increased dose to lung tissue can be predicted. For 100 patients, the use of uncorrected dose would result in an underestimation of the risk for radiological radiation pneumonitis by 7% on average and by as much as 19% maximally. These data suggest that whenever lung tissue and/or tumor response levels are critical, as is often the case for radical therapy, multi-center trials, and dose response determination, inhomogeneity corrections should be implemented.

Humans↗
PubMed1989

Radiation-induced lung damage: dose-time-fractionation considerations.

The comparison of different dose-time-fractionation schedules requires the use of an isoeffect formula. In recent years, the NSD isoeffect formula has been heavily criticized. In this report, we consider an isoeffect formula which is specifically developed for radiation-induced lung damage. The formula is based on the linear-quadratic model and includes a factor for overall treatment time. The proposed procedures allow for the simultaneous derivation of an alpha/beta ratio and a gamma/beta time factor. From animal data in the literature, the derived alpha/beta and gamma/beta ratios for acute lung damage are 5.0 +/- 1.0 Gy and 2.7 +/- 1.4 Gy2/day respectively, while for late damage the suggested values are 2.0 Gy and 0.0 Gy2/day. Data from two clinical studies, one prospective and the other retrospective, were also analysed and corresponding alpha/beta and gamma/beta ratios were determined. For the prospective clinical study, with a limited range of doses per fraction, the resultant alpha/beta and gamma/beta ratios were 0.9 +/- 2.6 Gy and 2.6 +/- 2.5 Gy2/day. The combination of the retrospective and prospective data yielded alpha/beta and gamma/beta ratios of 3.3 +/- 1.5 Gy and 2.4 +/- 1.5 Gy2/day, respectively. One potential advantage of this isoeffect formalism is that it might possibly be applied to both acute and late lung damage. The results of this formulation for acute lung damage indicate that time-dependent effects such as slow repair or proliferation might be more important in determining isoeffect doses than previously predicted by the estimated single dose (ED) formula. Although we present this as an alternative approach, we would caution against its clinical use until its applicability has been confirmed by additional clinical data.

Animals↗
PubMed1988

Quantitative measurement of changes in human lung density following irradiation.

In a recent clinical study, we have shown that computed tomography (CT) can provide a good qualitative endpoint for the presence of radiation-induced pulmonary damage. However, CT data are also potentially useful as a quantitative measure of lung damage. Changes in lung density were quantified by comparing CT images taken before and after radiotherapy for 54 patients. Lung densities were assessed separately in the irradiated and nonirradiated regions using both the average regional densities and density distributions. For the 36 patients demonstrating visible post-irradiation lung damage on CT, the mean relative increase in average lung density was 0.20 +/- 0.10 in the irradiated regions. The mean change in the nonirradiated regions was 0.02 +/- 0.09 for the same group. For 18 patients without visible damage, the mean relative changes were 0.00 +/- 0.09 and -0.05 +/- 0.07 for the irradiated and nonirradiated regions, respectively. The results suggest that an increase in average lung density of 5% or greater is associated with the visible detection of pulmonary damage. The dose-response relationship based on this quantitative criterion was comparable to that derived using the qualitative endpoint.

Electrons↗
PubMed1987

Acute radiation-induced pulmonary damage: a clinical study on the response to fractionated radiation therapy.

Acute radiation-induced pulmonary damage can be a significant cause of morbidity in radiation therapy of the thorax. A prospective, clinical study was conducted to obtain dose-response data on acute pulmonary damage caused by fractionated radiation therapy. The endpoint was a visible increase in lung density within the irradiated volume on a computed tomographic (CT) examination as observed independently by three diagnostic radiologists. Fifty-four patients with various malignancies of the thorax completed the study. CT chest scans were taken before and at preselected times following radiotherapy. To represent different fractionation schedules of equivalent biological effect, the estimated single dose (ED) model, ED = D X N-0.377 X T-0.058 was used in which D was the average lung dose within the high dose region in cGy, N was the number of fractions, and T was the overall treatment time in days. Patients were grouped according to ED and the percent incidence of pulmonary damage for each group was determined. Total average lung doses ranged from 29.8 Gy to 53.6 Gy given in 10 to 30 fractions over a range of 12 to 60 days. Five patient groups with incidence ranging from 30% (ED of 930) to 90% (ED of 1150) were obtained. The resulting dose-response curve predicted a 50% incidence level at an ED value (ED50) of 1000 +/- 40 ED units. This value represents fractionation schedules equivalent to a total average lung dose of 32.9 Gy given in 15 fractions over 19 days. Over the linear portion of the dose-response curve, a 5% increase in ED (or total dose if N and T remain constant), predicts a 12% increase in the incidence of acute radiation-induced pulmonary damage.

Adolescent↗
PubMed1987

Normal uveal melanocytes in culture.

Normal uveal melanocytes of rhesus and cynomolgus macaques can be grown in culture for 3-9 months and subcultured a few times. Postnatal and adult choroidal melanocytes are terminally differentiated cells. They are melanin-containing but not actively melanin-synthesizing cells. They do not undergo cell division, nor do they incorporate tritiated thymidine, but otherwise they are metabolically active. Postnatal and young adult iridial melanocytes are metabolically more active than choroidal cells. They require a feeder cell layer for attachment and to be maintained in a healthy condition. An endothelial cell line established from a rhesus fetal choroid-retina proves to be an effective feeder layer for adult iridial cells. Fetal uveal melanocytes divide slowly and usually require some stimulus and a special culture environment supplemented with 12-O-tetradecanolphorbol-13-acetate and cholera toxin. They can grow and differentiate in vitro. Iridial melanocytes grow and change into cells resembling postnatal choroidal melanocytes. Similar changes occur during development in utero. These findings further suggest that, in vivo, iridial melanocytes migrate and mature to become choroidal melanocytes.

Aging↗