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Biomedical subjects

M P Mehta

Publications and source records attributed to M P Mehta.

At least 73 records · Page 4Linked to original sources
PubMed1990

Monte Carlo and convolution dosimetry for stereotactic radiosurgery.

The dosimetry of small photon beams used for stereotactic radiosurgery was investigated using Monte Carlo simulation, convolution calculations, and measurements. A Monte Carlo code was used to simulate radiation transport through a linear accelerator to produce and score energy spectrum and angular distribution of 6 MV bremsstrahlung photons exiting from the accelerator treatment head. These photons were then transported through a stereotactic collimator system and into a water phantom placed at isocenter. The energy spectrum was also used as input for the convolution method of photon dose calculation. Monte Carlo and convolution results were compared with the measured data obtained using an ionization chamber, a diode, and film.

Brain Neoplasms↗
PubMed1990

90Y.B72.3 against pancreatic cancer: dosimetric and biological analysis.

Nude mice xenografted with a human pancreatic carcinoma cell line were injected with yttrium-90 (90Y) conjugated to diethylene triaminepenta acetic acid (DTPA) alone, and DTPA covalently linked to a monoclonal antibody, B72.3. The animals were sacrificed in temporal sequence to evaluate isotope distribution. Dosimetry was carried out using the principles outlined in MIRD and ICRU Report 32. Results are expressed as percent uptake per unit mass in organs and tumor and as relative absorbed dose normalized to 90Y uptake in liver at 7 hr. When conjugated to B72.3, an 8-fold increase in isotope localization in the tumor was noted by 24 hr. When the relative absorbed dose is calculated for 90Y and 90Y.B72.3, a 26-fold increase in tumor dose is noted for the 90Y conjugate. Normal tissues show no to modest (less than 5x) enhanced dose with 90Y.B72.3. B72.3, therefore, deserves further investigation as a potential monoclonal antibody for targeting therapeutic radioisotopes and possibly diagnostic radioisotopes to pancreatic cancer. Radiobiological aspects of the low dose rates from radioimmunotherapy are discussed.

Animals↗
PubMed1990

Minimization of small bowel volume within treatment fields utilizing customized "belly boards".

Thirty consecutive patients with pelvic malignancies were evaluated prospectively for the impact of a novel bowel minimization device ("belly board") on the volume of small bowel included within a four field pelvic radiation plan. A customized polyurethane and styrofoam bowel immobilization mold was created for each patient in the prone position. Using contrast enhanced CT scanning on a dedicated radiation treatment planning scanner, we imaged the location of the small intestine in the supine position and the prone position aided by the "belly board". Custom in-house interactive image analysis software was developed to allow volumetric determination of small bowel within the treatment portals. The mean small bowel volume was reduced by 66% (299 cm3 to 102 cm3), comparing the standard supine position to the prone position assisted by the "belly board". In 13 patients without prior pelvic surgery, the small bowel volume reduction was a more dramatic 74% (334 cm3 to 88 cm3). All patients were found to benefit from this prone "belly board" setup regardless of body habitus, weight, and age. Compliance with the set-up including use of bladder distension was excellent. All patients completed their pelvic radiotherapy without requiring a treatment break. Weight loss at completion averaged less than 5%. Seventy-six percent of patients experienced little or no diarrhea. This technique is comfortable, inexpensive, highly reproducible, and permits maximal bowel displacement from standard pelvic radiotherapy fields.

Adult↗
PubMed1990

Additive contribution of nitrous oxide to halothane MAC in infants and children.

Fifty-one infants and small children (14.7 +/- 7.2 mo) were studied to determine the MAC of halothane in O2 (n = 11) and in the presence of three different nitrous oxide (N2O) concentrations (25% [n = 13], 50% [n = 13], and 75% [n = 14]). In the three N2O groups, after randomly assigning patients to an N2O group, anesthesia was induced with halothane and N2O using a pediatric circle system. After endotracheal intubation, halothane and N2O end-expired concentrations were adjusted to predetermined concentrations. The initial halothane concentrations in each group were based on the assumption that each percent N2O reduced halothane concentrations by 0.01 vol % (assumed halothane MAC = 1.0 vol %). Based on the response of the preceding subject in each group, halothane concentrations were increased or decreased depending on whether the response was to move or not to move, respectively, in response to the surgical incision. The mean duration of constant end-tidal concentrations before skin incision was 10 min. End-tidal gases were sampled and measured from a separate distal sampling port of an endotracheal tube during controlled ventilation (Perkin-Elmer Mass Spectrometer). The MAC value for halothane in O2 was 0.94 +/- 0.08 vol % (mean +/- SD). The MAC values of halothane in the presence of 25%, 50%, and 75% N2O were 0.78 +/- 0.12 vol %, 0.44 +/- 0.10 vol %, and 0.29 +/- 0.06 vol %, respectively. All concentrations of N2O significantly reduced the MAC of halothane. A regression analysis through all four data points yielded a linear relationship (r2 = 0.87) with a predicted MAC for N2O of 105 vol %. Unlike halothane and isoflurane, the predicted MAC of N2O in infants and children is similar to that reported by others in adults. Similar to the results of clinical studies in adults, the contribution of N2O to halothane MAC in children is additive.

Anesthesia, Inhalation↗
PubMed1990

Third place 1989 Alpha Cradle Award winner. Technical aspects in the use of "belly boards" for small bowel minimization.

The position in which a patient is treated for pelvic irradiation has been shown to have dramatic significance in regard to the volume of small bowel within the treatment field. Previous studies in the literature have repeatedly supported the fact that volume may be the leading factor in both acute and chronic morbidity. We have prospectively evaluated and treated 30 patients utilizing a custom-made polyurethane foam and styrofoam "belly board" with a dropout cut from the level of the xyphoid process to the superior border of the treatment field, specifically designed to allow maximal superior and anterior displacement of small bowel by bladder distention and gravity, while allowing reliable daily reproducibility, accurate immobilization and equally important, increased patient comfort and compliance. By evaluating all patients (in both the supine position alone, and prone in the "Belly Board") with a dedicated treatment planning CT scanner, we have been able to achieve 80-100% reduction in the volume of small bowel within the radiation portals. We will discuss data on the technical set-up, cost, and variations which allow the "Belly Board" to be specifically tailored for use when treating other intraabdominal sites. This technique is simple, inexpensive, highly reproducible, and permits maximal bowel displacement outside the treatment fields.

Adult↗
PubMed1989

Neuromuscular and cardiovascular effects of mivacurium chloride in surgical patients receiving nitrous oxide-narcotic or nitrous oxide-isoflurane anaesthesia.

The neuromuscular and cardiovascular effects of mivacurium chloride were studied during nitrous oxide-oxygen narcotic (fentanyl) (n = 90) and nitrous oxide-oxygen isoflurane (ISO) anaesthesia (n = 45). In addition, a separate group (n = 9) received succinylcholine during fentanyl anaesthesia to compare its neuromuscular effects with mivacurium. Mivacurium was initially administered as a single bolus in doses from 0.03 mg.kg-1 to 0.25 mg.kg-1 to study the dose-response relationships, as well as the cardiovascular effects of mivacurium. Neuromuscular block (NMB) was measured by recording the twitch response of the adductor pollicis muscle following ulnar nerve stimulation (0.15 Hz, 0.2 ms supramaximal voltage). The ED95 values for mivacurium were estimated to be 0.073 mg.kg-1 and 0.053 mg.kg-1 in the fentanyl and ISO groups respectively. The duration of block (time from injection to 95 per cent recovery) for a dose of 0.05 mg.kg-1 mivacurium was 15.3 +/- 1.0 min and 21.5 +/- 1.3 min for fentanyl and ISO anaesthesia, respectively. The recovery index (25-75 per cent) between initial bolus dose (6.1 +/- 0.5 min), repeat bolus doses (7.6 +/- 0.6 min), mivacurium infusion (6.7 +/- 0.7 min) and succinylcholine infusion (6.8 +/- 1.8 min) were not significantly different. There was minimal change in mean arterial pressure (MAP) or heart rate (HR) following bolus doses of mivacurium up to 0.15 mg.kg-1. Bolus administration of 0.20 mg.kg-1 or 0.25 mg.kg-1 of mivacurium decreased MAP from 78.2 +/- 2.5 to 64.0 +/- 3.2 mmHg (range 12-59 per cent of control) (P less than 0.05). The same doses when administered slowly over 30 sec produced minimal change in MAP or HR.

Adult↗
PubMed1989

Endobronchial irradiation for malignant airway obstruction.

An afterloading endobronchial irradiation (EBRT) technique using Iridium-192 (Ir-192), was piloted for malignant airway obstruction. Under bronchoscopic guidance, a catheter is threaded distal to the lesion. Orthogonal radiographs and computerized tomographic (CT) scans are obtained for dosimetry. Forty implants in 38 patients have been performed. Thirty-two patients had lung cancer; 23 had received prior irradiation and eight had prior chemotherapy. Eight patients underwent pre-endobronchial irradiation laser excision. Median implant duration was 50.5 hr; median dose at 1 and 2 cm from source center was 50 and 20 Gy, respectively. The procedure was well tolerated with four long-term complications (10.5%). Twelve of 38 patients are currently alive with a median survival of 5+ months and a range of 1 to 21+ months. Changes in performance status (PS), symptom resolution, radiographic demonstration of re-aeration of atelectatic lung, changes in pulmonary function (PFT), and post-endobronchial irradiation bronchoscopy were used to assess response. Seventy percent of the patients' remaining life was rendered symptom-free or improved. A 70% radiographic response was noted. Fourteen patients underwent post-endobronchial irradiation bronchoscopy with 12 complete responses. Endobronchial irradiation, therefore, appears to be a safe, effective technique to palliate malignant airway obstruction.

Airway Obstruction↗
PubMed1989

Radiation induced thyroid neoplasms 1920 to 1987: a vanishing problem?

Radiation for benign diseases has been implicated as an etiologic factor in thyroid cancer. From 1930-60, over 2 million children may have been exposed to therapeutic radiation and it is estimated that up to 7% may develop thyroid cancer after a 5-40 year latency. Thyroid stimulating hormone, secondary to radio-induced hypothyroidism, has been implicated as causative in animals. Such data has led to expensive screening programs in high risk patients. Because of a decline in irradiation for benign diseases in children over the last 2 decades, we questioned whether the incidence of radiation induced thyroid neoplasms (RITN) was also decreasing. Twenty-six of 227 patients (11%) with thyroid malignancies seen at our institution from 1974-87 had a history of previous head and neck irradiation. These included 13 papillary, 3 follicular, and 7 mixed carcinomas as well as 2 lymphomas and 1 synovial cell sarcoma. None of these 26 patients had abnormal thyroid function tests at presentation. Mean latency from irradiation to the diagnosis of thyroid cancer was 25.4 years (6-55 year range). Compared to the reported increasing incidence of RITN from 1940-70, there appears to be a significant decrease since 1970. Based on our analysis, the use of expensive screening programs in high risk populations may no longer be warranted. Additionally, the routine use of thyroid replacement in previously irradiated chemically hypothyroid patients is not recommended.

Adolescent↗
PubMed1989

Serum potassium concentrations following succinylcholine in patients undergoing beta-adrenoceptor blocking therapy.

Efflux of serum potassium following succinylcholine was compared in surgical patients undergoing low-dose, long-term beta 1-adrenoceptor or beta 1,2-adrenoceptor blocking therapy and in those receiving neither of these therapies. There were no significant differences in serum potassium concentration prior to, and over a study period of, 2 hours following succinylcholine administration among the three groups of patients.

Administration, Oral↗
PubMed1989

Anterior dislocation of the shoulders with bilateral brachial plexus injury.

A case of bilateral anterior shoulder dislocation accompanied by bilateral brachial plexus injuries is presented. A 53-year-old man fell and landed on his chest and arms flexed at the elbows. The dislocations were satisfactorily reduced using the forward elevation, flexion maneuver. Electromyography and nerve conduction studies confirmed bilateral brachial plexus lesions. Arthrogram of the right shoulder demonstrated a rotator cuff tear. The patient is undergoing physical therapy and making a slow recovery.

Brachial Plexus↗
PubMed1989

Adult Wilms' tumor. Role of combined modality treatment.

Adults Wilms' tumor, unlike its pediatric counterpart, is extremely rare and highly lethal. Less than 200 cases have been reported in the world literature and a large proportion of these may not have been true Wilms' tumors. We report 3 cases seen at our institution who were treated with a multimodality approach, all three remaining alive without evidence of active disease at 6 years, 2.25 years and 8 months respectively from diagnosis. We also review results of multimodality management, emphasizing the poor outcome for stage III and IV tumors in spite of multi-agent chemotherapy. Alternative drugs, such as cisplatinum may have a role in management. Finally, we propose that prophylactic pulmonary irradiation may have a place in advanced stages of adult Wilms' tumor.

Adolescent↗
PubMed1989

A comparative study of methods of detection of esophageal intubation.

The trachea and esophagus of 21 patients were simultaneously intubated to comparatively evaluate methods for detecting esophageal intubation. In succession, the trachea and esophagus were ventilated with the same inspiratory volume of 621 +/- 45 mL (mean +/- SD). Carbon dioxide (CO2) levels, volumes, and temperatures of expired gas were measured from the tracheal and esophageal tubes. End-expired CO2 levels of gases from the trachea and esophagus were 4.9 +/- 0.7% and 0.6 +/- 0.6%, respectively, with CO2 waveforms observed in 7 (33%) patients with esophageal intubations. Volumes expired from the tracheal tube averaged 615 +/- 64 mL and from the esophageal tube 35 +/- 16 mL (P less than 0.001). Peak temperatures of expired gas recorded from the tracheal tube (32.0 +/- 0.73 degrees C) were higher than those from the esophageal tube (27.3 +/- 1.2 degrees C) (P less than 0.001). The shape of temperature waveforms with a correctly placed tracheal tube remained constant with each ventilation, contrary to that obtained from an esophageal tube. Although the occasional detected of CO2 waveforms from an esophageal tube might lead to an incorrect assessment of tube placement, this limitation of CO2 analyzer can be offset by measurement of volume and temperature of expired gas in identifying placement of an endotracheal tube.

Carbon Dioxide↗
PubMed1988

The neuromuscular blocking and cardiovascular effects of doxacurium chloride in patients receiving nitrous oxide narcotic anesthesia.

The purpose of this study was to evaluate neuromuscular and cardiovascular effects of doxacurium chloride, a new long-acting neuromuscular blocking agent, during a stable state of nitrous oxide and narcotic anesthesia. Ninety-three ASA physical status I or II patients were studied after informed written consent had been obtained. Eighty-one patients (group A) received doxacurium. The 81 patients were divided into nine subgroups according to the dose of doxacurium administered (0.01-0.06 mg.kg-1). Patients in a control group (group B) (n = 12) received pancuronium. To assess neuromuscular responses, a force displacement transducer recorded the twitch response of the adductor pollicis muscle following ulnar nerve stimulation. The ED50 and ED95 for doxacurium were estimated to be 0.013 mg.kg-1 and 0.023 mg.kg-1, respectively. The time to maximum twitch suppression following a dose of 1.0 (ED95) and 1.7 (ED95) was 10.3 +/- 1.3 min and 7.6 +/- 0.8 min, respectively. After an ED95 dose of doxacurium the time to spontaneous recovery to 95% of control twitch height was 73.7 +/- 8.7 min. With larger doses of doxacurium, 0.04 mg.kg-1 (1.7 X ED95) and 0.05 mg.kg-1 (2.2 X ED95), the time to spontaneous recovery to 95% of control twitch height was 125.8 +/- 24.8 and 204.0 +/- 21.2 minutes, respectively. When 25% twitch height recovery or more was present the reversal of doxacurium induced neuromuscular blockade was prompt.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Comparison of psychologic and cognitive functions after general or regional anesthesia.

The behavior of 105 patients randomly assigned to receive either general or regional anesthesia and who underwent one of three types of surgery (hysterectomy, prostatectomy, or joint replacement) was assessed before, immediately after, and 3 mo after surgery. Psychologic status was assessed by the Sickness Impact Profile, the SCL-90-R, and a Metamemory Questionnaire. Cognitive functioning was measured by a battery of ten psychomotor, memory, and skilled performance tasks. Physical health was scored by the ASA classification of physical status, a health index, postoperative complications ratings, and a self-rated measure of the patient's health. There were cognitive differences across surgery groups due to age and gender variability among the patients; however, the type of anesthesia produced no difference in behavior. Both the physical and mental health indices showed improvement from the preoperative to the postoperative periods. General anesthesia appears to pose no risk to mental function and recovery beyond that associated with regional anesthesia and surgery.

Adult↗
PubMed1988

An analysis of critical incidents in a teaching department for quality assurance. A survey of mishaps during anaesthesia.

A prospective survey was conducted from April 1984-January 1985 and April 1985-January 1986 to study the frequency of critical incidents and factors associated with them. Eighty-six mishaps were reported in the first period, the majority of which were because of human error (80.3%); the most common were the transmission of gases and vapours and errors in drug administration. Factors frequently associated with these mishaps were failure to perform a normal check and lack of familiarity with equipment or technique. An anaesthesia equipment checklist was incorporated in the survey during the second period and 43 mishaps were reported. This decrease in incidence may have resulted from the anaesthesia apparatus checklist, awareness of mishaps since they were discussed regularly at departmental meetings, and new anaesthesia machines (eight older machines were replaced during the first period and 11 at the beginning of the second).

Accidents↗
PubMed1988

Treatment of probable subclinical liver metastases and gross pancreatic carcinoma with hepatic artery 5-fluorouracil infusion and radiation therapy.

Since subclinical hepatic metastases are frequently present at time of diagnosis of pancreatic carcinoma, any meaningful effort to improve survival must include 'prophylactic' liver therapy in addition to treatment of the pancreatic primary. We report the results of a prospective, unrandomized clinical trial of a 2-week liver and pancreas infusion (by hepatic artery) of 5-fluorouracil (5-FU) and pancreatic irradiation to 50-60 Gy, combined with prophylactic irradiation of the liver with approximately 20 Gy. Of 21 evaluable patients, 17 completed therapy without excessive toxicity and had a median survival of 50 weeks. Contrary to historical controls, the liver in our series was rarely the first site of failure (6%), suggesting that the combination of hepatic artery 5-fluorouracil and 20 Gy liver radiation may suppress subclinical (microscopic) liver metastases without significant hepato-toxicity. When radiation doses to the pancreas were increased above 50 Gy there was improvement in primary tumor control, although failure in the pancreatic bed remained the most common site of failure. Future clinical investigation of this form of combined therapy for eradication of micro-metastasis in the liver, combined with more aggressive local pancreatic therapy, would seem appropriate.

Adenocarcinoma↗