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Biomedical subjects

R Mohan

Publications and source records attributed to R Mohan.

At least 19 recordsLinked to original sources
PubMed1992

Quality of life after open heart surgery 16-18 May 1991.

This is a review of papers presented at the international symposium on 'Quality of Life after Open Heart Surgery' comprising the experience in more than 20,000 patients. Early identification and operation of premorbid personalities, psychological counselling before and after the operation, explanation of true risks, an educational programme in redefinition of family roles, stressing the importance of returning to normal activity in education, employment and society, financial support through health insurance to cover the high cost of open heart surgery, and formulating socioeconomic policies which encourage returning to work yield improvement in all patient groups. Specific to valve replacement is patient participation in deciding the kind of prosthesis and improvement of anticoagulation strategies. Coronary bypass patients benefit broadly through a comprehensive rehabilitation programme. For congenital heart disease, emphasis was laid on the need to educate parents about the disease, the importance of open discussion between parents, the patient and the paediatric cardiologist, and the function of a parents' self-help group. For heart transplantation the endeavour must be to increase donor availability and to develop better immunosuppression schedules. Lastly, general awareness of patients' abilities will facilitate their social integration and improve their quality of life.

Adult↗
PubMed1992

Improved endothelial viability of heart valves cryopreserved by a new technique.

The aim of this study was to compare different techniques of aortic valve cryopreservation by studying the viability of the endothelial cells. Viability was assessed by measuring their in vitro prostacyclin (PGI2) production under basal and stimulated conditions. Fresh and cryopreserved porcine valves were incubated at 37 degrees C in tissue culture medium and PGI2 content in the medium was measured every 15 min up to 300 min. Cryopreservation by the older procedure A included 5% fetal calf serum (FCS) in the preservation medium, a plastic box inside a freezing plastic bag, a cooling schedule approximating -2 degrees C/min, a long thawing time and few dilution steps of the cryoprotectant dimethylsulphoxide (DMSO). The newer procedure B differed from A in packaging, freezing and thawing rates and DMSO dilution. Procedure C was similar to B with the exception that FCS was omitted. Leaflets preserved by procedure A produced significantly less prostacyclin as compared to those treated according to procedures B or C. We conclude that minor differences in the cryopreservation method can become critical to endothelial functional viability.

Animals↗
PubMed1992

Isolated coronary artery bypass grafting in patients 75 years of age and older: is age per se a contraindication?

137 patients with a mean age of 77.3 years (Group A) who underwent isolated coronary artery bypass grafting (CABG) were compared to 137 patients with a mean age of 55.6 years (Group B) who also underwent isolated CABG on the same or the adjacent day as the Group A patients. Group A patients were more commonly women, and had a significantly higher incidence of unstable angina, emergency operations, extensive coronary disease, peripheral vascular disease, and multiorgan debility. However, their left-ventricular function and the extent of revascularisation was similar to Group B patients. They also had significantly more operative mortality (7.2% vs 1.45%, p < 0.001). cardiac and non-cardiac complications, and longer hospital stay (14.2 vs 8.8 days, p < 0.001) than group B patients. At a mean follow-up of 29.8 months, no significant differences were noted in Group A versus Group B patients in terms of long-term survival (95% vs 94%), freedom from angina (82% vs 81%), cardiac readmission (10% vs 12%), or in the incidence of new myocardial infarction or new CABG. Actuarial survival at 4 years was 76.9% in Group A patients and 90.1% in Group B patients. Severe angina due to extensive coronary disease commonly makes urgent surgery unavoidable in this growing population of very old patients, but the operative mortality is modest and survivors do enjoy several years of life, remaining as free of angina, etc., as similar but younger patients.

Actuarial Analysis↗
PubMed1992

Coronary artery bypass grafting in the elderly--a review of studies on patients older than 64, 69 or 74 years.

21 studies reporting on at least 100 elderly patients were reviewed to assess the influence of patient age on outcome of isolated coronary artery bypass surgery. Elderly patients were variously defined as being older than 64, 69 or 74 years of age. They had significantly higher incidences of female sex, unstable angina, urgent surgery, extensive coronary disease, peripheral vascular disease and other risk factors, but left ventricular function was similar to younger patients. The number of grafts inserted and operation times were also similar. Operative mortality and multiorgan morbidity were significantly higher with advancing age. Late survival and relief of angina were generally good.

Age Factors↗
PubMed1992

Quality of life after heart valve replacement.

Over the last three decades, heart valve replacement has become a safe and routine surgical procedure, but replacement devices are still far from ideal. Despite improvements in materials and design, life-long anticoagulation remains mandatory for mechanical valves. The major shortcoming of the less thrombogenic bioprosthetic valves is early tissue failure. Parallel to the decrease in operative mortality after heart valve replacement, the potential quality of life for survivors has been becoming increasingly important in evaluating the late results and in selecting the appropriate device for the given patient. All factors that determine the quality of life are strongly affected by the operation due to the usually dramatic improvement both in subjective status and objective parameters postoperatively. The patient, thus, can return to normal activities, maintain self-esteem and keep normal relationships at work, in the community and at home. Psychoneurologic dysfunction was also found to decrease greatly within six months, although more than a quarter of patients were depressed preoperatively because of their disease. Overall, the experience was generally satisfying.

Adaptation, Psychological↗
PubMed1991

Interinstitutional experience in verification of external photon dose calculations.

Under the auspices of NCI contracts, four institutions have collaborated to assess the accuracy of the pixel-based dose calculation methods they employ for external photon treatment planning. The approach relied on comparing calculations using each group's algorithm with measurements in phantoms of increasing complexity. The first set of measurements consisted of ionization chamber measurements in water phantoms in normally incident square fields, an elongated field, a wedged field, a blocked field, and an obliquely incident beam. The second group of measurements was carried out using thermoluminescent dosimeters in phantoms designed to investigate the effects of surface curvature, high density heterogeneities, and low density heterogeneities. The final study tested the entire treatment planning system, including CT data conversion, in an anthropomorphic phantom. Overall, good agreement between calculation and measurements was found for all algorithms. Regions in which discrepancies were observed are pointed out, areas for algorithm improvement are identified and the clinical import of algorithm accuracy is discussed.

Humans↗
PubMed1991

Dose-volume histograms.

A plot of a cumulative dose-volume frequency distribution, commonly known as a dose-volume histogram (DVH), graphically summarizes the simulated radiation distribution within a volume of interest of a patient which would result from a proposed radiation treatment plan. DVHs show promise as tools for comparing rival treatment plans for a specific patient by clearly presenting the uniformity of dose in the target volume and any hot spots in adjacent normal organs or tissues. However, because of the loss of positional information in the volume(s) under consideration, it should not be the sole criterion for plan evaluation. DVHs can also be used as input data to estimate tumor control probability (TCP) and normal tissue complication probability (NTCP). The sensitivity of TCP and NTCP calculations to small changes in the DVH shape points to the need for an accurate method for computing DVHs. We present a discussion of the methodology for generating and plotting the DVHs, some caveats, limitations on their use and the general experience of four hospitals using DVHs.

Humans↗
PubMed1991

The role of uncertainty analysis in treatment planning.

The role of uncertainty analysis in 3-D treatment planning systems was addressed by four institutions which contracted with NCI to evaluate high energy photon external beam treatment planning. Treatment plans were developed at eight disease sites and the effects of uncertainties assessed in a number of experiments. Uncertainties which are patient-site specific included variations in the delineation of target volumes and normal tissues and the effects of positional uncertainties due to physiological motion and setup nonreproducibility. These were found to have a potentially major impact on the doses to the target volumes and to critical normal tissues which could result in significantly altered probabilities of tumor control and normal tissue complications. Other uncertainties, such as the conversion of CT data to electron densities, heterogeneities and dose calculation algorithms' weaknesses, are related to physical processes. The latter was noted to have the greatest potential contribution to uncertainty in some sites. A third category of uncertainty related to the treatment machine, the consequences of compensator misregistration, are exclusive to the site and the treatment portal. Because conventional treatment planning systems have not incorporated uncertainty analysis, tools and techniques had to be devised for this work; further development in this area is needed. Many of the analyses could not have been done without full 3-D capabilities of the planning systems, and it can be anticipated that the availability of uncertainty analysis in these systems which allow nontraditional beam arrangements will be of great value.

Humans↗
PubMed1991

Histogram reduction method for calculating complication probabilities for three-dimensional treatment planning evaluations.

New tools are needed to help in evaluating 3-D treatment plans because of the large volume of data. One technique which may prove useful is the application of complication probability calculations. A method of calculating complication probabilities for inhomogeneously irradiated normal tissues is presented in this paper. The method uses clinical estimates of tolerance doses for a few discreet conditions of uniform partial organ irradiation, an empirical fit of a continuous function to these data, and a technique (the effective volume method) for transforming nonuniform dose-volume histograms into equivalent uniform histograms. The behavior of the effective volume histogram reduction method for various boundary conditions is reviewed. The use of complication probabilities in evaluating treatment plans is presented, using examples from an NCI 3-D treatment planning contract.

Humans↗
PubMed1991

Numerical scoring of treatment plans.

This is a report on numerical scoring techniques developed for the evaluation of treatment plans as part of a four-institution study of the role of 3-D planning in high energy external beam photon therapy. A formal evaluation process was developed in which plans were assessed by a clinician who displayed dose distributions in transverse, sagittal, coronal, and arbitrary oblique planes, viewed dose-volume histograms which summarized dose distributions to target volumes and the normal tissues of interest, and reviewed dose statistics which characterized the volume dose distribution for each plan. In addition, tumor control probabilities were calculated for each biological target volume and normal tissue complication probabilities were calculated for each normal tissue defined in the agreed-upon protocols. To score a plan, the physician assigned a score for each normal tissue to reflect possible complications; for each target volume two separate scores were assigned, one representing the adequacy of tumor coverage, the second the likelihood of a complication. After scoring each target and normal tissue individually, two summary scores were given, one for target coverage, the second reflecting the impact on all normal tissues. Finally, each plan was given an overall rating (which could include a downgrading of the plan if the treatment was judged to be overly complex).

Humans↗
PubMed1991

Three-dimensional photon treatment planning for carcinoma of the nasopharynx.

The role of 3-D treatment planning for carcinoma of the nasopharynx was assessed in a four institution study. Two patients were worked up and had an extensive number of CT scans on which target volumes and normal tissues were defined. Treatment planning was then performed using state of the art dose planning systems for these patients to assess the value of the new technology. In general, it was demonstrated that multi-field conformal plans could achieve good tumor dose coverage, while at the same time reducing normal tissue doses, compared to standard treatment planning techniques. The role of inhomogeneity corrections, beam energy, and the use of CT vs. simulation films for defining target volumes were also discussed. In addition, techniques to evaluate 3-D plans for the nasopharynx were considered, and some analysis of this problem is presented in this paper.

Adult↗
PubMed1991

Three-dimensional photon treatment planning in carcinoma of the larynx.

The role of three-dimensional (3-D) treatment planning in the definitive treatment of carcinoma of the larynx with radiation was evaluated at four institutions as part of an NCI contract. A total of 30 different treatment approaches were devised for two patients with larynx cancer. CT scans were obtained for both patients and various treatment planning tools were employed to optimize beam arrangements and to evaluate the resulting dose distribution. The effect on dose distribution of a number of factors was also examined: 1) the use of dose calculation algorithms which correct for tissue inhomogeneities, 2) the variation of the CT numbers used for inhomogeneity corrections to simulate inaccuracies in the knowledge of the CT numbers, and 3) the modification of beam energy. A multitude of data was used in plan evaluation and a numerical score was given to each plan to estimate the tumor control probability and the normal tissue complication probability. We found 3-D treatment planning to be of potential value in optimizing treatment plans in larynx cancer. Improved target coverage was achieved when complete information describing 3-D geometry of the anatomy was utilized. In some cases, the treatment planning tools employed, such as the beam's eye view, helped devise novel beam arrangements which were useful alternatives to standard techniques. We found little effect of change in CT number on dose distributions. A comparison between dose distributions calculated with tissue inhomogeneity corrections to those calculated without this correction showed little difference. We did find some improvement in the dose to the primary tumor volume at lower beam energies, but with an increased larynx volume potentially receiving doses above tolerance.

Adult↗
PubMed1991

A genetic study of retinopathy in south Indian type 2 (non-insulin-dependent) diabetic patients.

Genetic marker studies in diabetic retinopathy are controversial and frequently complicated by possible independent associations of Type 1 (insulin-dependent) diabetes mellitus with the markers so far analysed. We have looked for associations of candidate genes with retinopathy in South Indian Type 2 (non-insulin-dependent) diabetic patients; patients were subdivided into those with exudative maculopathy (n = 53), proliferative retinopathy (n = 40) and patients free from diabetic retinopathy with a minimum disease duration of 15 years (n = 45). DNA was extracted from blood samples and studied by Southern blot hybridisation techniques and the following probe enzyme combinations: HLA-DQB1; Taq 1, HLA-DQA1; Taq 1, HLA-DRA; Bgl II, insulin gene hypervariable region; Pvu II and the switch region of the immunoglobulin IgM heavy chain gene (S mu); Sac I. Differences in genotype distributions between the study groups were only detected with the S mu probe which detects polymorphism of both S mu and S alpha 1 (the switch region of IgA). Two alleles of S alpha 1 were detected sized 7.4 kilobase and 6.9 kilobase. The frequency of 6.9 kilobase homozygotes was lower in proliferative retinopathy (19%) compared to patients free from diabetic retinopathy (54%, p = 0.005) and exudative maculopathy (46%, p = 0.03). This data suggests that there is a genetic predisposition to proliferative retinopathy in Type 2 (non-insulin-dependent) diabetes of South Indian origin and that this is determined by polymorphism of the heavy chain immunoglobulin genes located on chromosome 14.

Aged↗
PubMed1991

Improved dose distributions for 3D conformal boost treatments in carcinoma of the nasopharynx.

This study was designed to demonstrate the feasibility of 3-dimensional (3D) treatment planning in patients with carcinoma of the nasopharynx, and to explore its potential therapeutic advantage over the traditional 2-dimensional (2D) approach in this disease. Qualitative and quantitative comparisons between the two techniques were made for the boost portion of the treatment (19.8 Gy of a total 70.2 Gy treatment schedule) in 10 previously untreated patients and for the entire treatment in 5 patients with locally recurrent disease. The 2D and 3D plans were compared in each patient using dose-volume histograms (DVH's), tumor control probabilities (TCP's), normal tissue complication probabilities (NTCP's), and a new biologic figure of merit that describes the probability of uncomplicated control. Although there was no attempt to optimize the 3D treatment approach by using this method throughout the total treatment course (rather than for the boost only), it was still found that for each of the endpoints examined the 3D approach resulted in improved plans. An average of 22% of the target volume was underdosed at the 95% isodose level with the 2D plans compared to 7% with the 3D plans. The improved treatment planning by 3D increased the mean dose to the tumor volume by an average of 13% over 2D planning. The dose to normal structures such as the mandible and parotid glands was reduced with the 3D plans while the brain stem and spinal cord remained within tolerance limits. The probability of uncomplicated tumor control was increased by an average of 15% with 3D treatment planning compared to the 2D approach. Our findings demonstrate the potential of 3D planning for improving the treatment of carcinoma of the nasopharynx, but prospective studies are required to define the true clinical advantages of this methodology.

Humans↗