Search PubMed⌕ Search

Biomedical subjects

S Vijayakumar

Publications and source records attributed to S Vijayakumar.

At least 127 records · Page 7Linked to original sources
PubMed1989

Human neoplasm pH and response to radiation therapy: P-31 MR spectroscopy studies in situ.

Thirty-five human neoplasms from various sites and of various histologic types and stages were examined with phosphorus-31 magnetic resonance spectroscopy in situ. The tumors included 13 squamous cell carcinomas of the head and neck (lymph nodes), eight Hodgkin lymphomas, six non-Hodgkin lymphomas, four carcinomas of the breast, one melanoma, one sarcoma, one neuroblastoma, and one mucoepidermoid sarcoma of the salivary glands. Thirty-four of the neoplasms had normal to slightly alkaline pH before irradiation. During fractionated radiation therapy, the pH stayed in a range of from near neutral to alkaline and rose to 7.6-8.0 at several time points of radiation therapy for some tumors. These results suggest that most tumor cells in human neoplasms are well oxygenated and that only a negligible fraction are chronic hypoxic cells. The fluctuating alkaline pH during radiation therapy occurred regardless of the responsiveness of the treated tumors.

Carcinoma, Squamous Cell↗
PubMed1989

Less well known parameters of in vitro radiosensitivity.

In addition to well known parameters used for measuring in vitro cellular radiosensitivity (mean lethal dose, extrapolation number, quasithreshold dose), there are other, less well known measures that may be more important. The authors recently surveyed the literature and found that mean activation dose (D) has been neglected in the analyses. Among 70 articles published in the radiation oncology and biology literature that used cell survival curves or parameters to measure radiosensitivity, only two used the values of D in their analysis. By recalculating D from published survival curves, different conclusions may be drawn. The authors see a definite need for more prospective application of D and surviving fraction at 2 Gy.

Cell Survival↗
PubMed1988

Treatment of pulmonary mycosis fungoides with whole-lung radiation therapy.

Visceral involvement is a relatively common but poorly appreciated occurrence in patients with mycosis fungoides. The lungs are the most common site of visceral involvement. Here we present two cases of mycosis fungoides with pulmonary parenchymal involvement, one of them proven by biopsy. Both patients were treated with whole-lung radiation therapy, with complete disappearance of the lesions and improvement of respiratory symptoms. There was no significant radiation-induced pulmonary toxicity. One patient continues to be alive with no recurrence in the lungs 17 months after radiation therapy.

Adult↗
PubMed1988

Posterior spinal cord block: a dosimetric study.

To determine the optimal width of a midline posterior spinal block (MPSB) (to avoid delivering too great a dose to the cord and too small a dose to adjacent tissue), the authors determined with magnetic resonance (MR) imaging normal ranges of cord depth and width and correlated them with film dosimetric data. In 59 randomly selected patients there was a wide range for both depth and width. The average depths of the anterior and posterior surfaces of the cord were 6.7 cm +/- 1.4 and 5.4 cm +/- 1.3, respectively. The average cord width was 1.6 cm +/- 0.4. Optimal cord block width as a function of cord width was determined for a 6-MV photon beam. The optimal cord block width at the surface (half-value layer [HVL] thickness = 6) varied from 1.5 to 3.0 cm for cord widths of 0.8-2.4 cm, which correspond to two standard deviations from the average. There was no significant dependence on depth of the cord. For optimal treatment outcome, the MPSB width may have to be determined for each patient individually.

Film Dosimetry↗
PubMed1987

Response of a non-Hodgkin lymphoma to 60Co therapy monitored by 31P MRS in situ.

High quality 31P MR spectra (signal to noise ratio (S/N) approximately 18, 15 min acquisition for each spectrum) were consistently obtained with surface coils over a period of 6-week RT. Both transient and steady state alterations in metabolites in response to RT were found in this case. The transient changes occurred during the first 3 hr immediately after the 3rd fractionated RT, these changes include the transient elevation of the PCr resonance, a decrease in PDE and an increase in intracellular pH. The monitoring showed that the metabolites approached steady state approximately 2 hr after the fractionated radiation intervention, suggesting that in vivo MRS can be useful for studying the dynamics of tumor response to RT such as repair of potential lethal damage, growth delay, and reoxygenation etc. The steady-state MR spectra showed the net response to each intervention and can clinically be useful for predicting and measuring the result of the fractionated RT. In this case study, the PDE peak which contains the phospholipid metabolites GPC and GPE, is the most sensitive resonance in response to RT. After the 3rd RT, prior to tumor size reduction, the PDE to ATP ratio decreased 33% and intracellular pH increased to 7.34 +/- 0.05 from 7.27 +/- 0.05. In the subsequent RT interventions, both the tumor size and PDE/ATP ratio continually decreased whereas the pH values remained alkaline and fluctuated around 7.34 to 7.65. The data suggest that the phospholipid metabolite PDE may signal important alterations in membrane metabolism that eventually lead to cell death.

Cobalt Radioisotopes↗
PubMed1987

Brachytherapy implants with differently spaced Ir-192 seeds: a dosimetric study.

Brachytherapy implantations traditionally have been carried out with continuous line sources of radium. With the popularity of afterloading implantations, iridium-192 seeds in plastic ribbons have replaced radium in the United States, although continuous sources, such as iridium wires, are widely used in Europe. The authors analyzed the impact of the use of noncontinuous sources in brachytherapy implants. Computer simulations and film dosimetry of a two-planar implant were carried out. Seeds at standard spacing (1 seed/cm), nonstandard spacing (1 seed/6mm), and continuously arranged seeds were studied.

Brachytherapy↗
PubMed1986

Metastasis to the hand.

Metastasis to the hand is a rare occurrence. Here the authors report a case of metastasis to the hand, which typifies the natural history and behavior of this uncommon manifestation of malignancy. Incidence, sites of origin, presentation, and diagnosis are discussed. The aim of treatment is palliation. The rationale for selecting either radiation therapy or surgery is presented.

Adenocarcinoma↗
PubMed1985

Medulloblastoma therapy using electron beams.

The use of megavoltage photons for the spinal component of cerebrospinal axis irradiation is responsible for most of the long-term sequelae in children with medulloblastomas who undergo this procedure. The technique and advantages of using electrons for this component of the procedure are described.

Adolescent↗
PubMed1985

Medulloblastoma: are we overtreating?

Modern advances in the concept and the techniques of megavoltage radiation therapy have revolutionized the treatment of medulloblastoma. Five-year survivals of 50 to 70 percent are achieved by craniospinalaxis irradiation with a boost to the posterior fossa. However, the price paid by the long-term survivors is significant. Sequelae include growth retardation, thyroid deficiency and anomalies, marrow suppression, gonadal irradiation, IQ and psychological deterioration, immunological alterations, second malignancies, and pituitary hormonal deficiencies.The literature is reviewed in terms of these sequelae and analyzed to determine optimal therapeutic doses. Although the authors agree with the doses used to treat the posterior fossa, the current doses recommended to eradicate the microscopic disease in the rest of the neuroaxis appear excessive; a lesser dose can be as effective and may decrease the rate and severity of complications.The authors believe that there is enough evidence to initiate a randomized, multi-institutional clinical trial using 20 to 25 Gy to the neuraxis (other than the posterior fossa) in one of the arms, especially when there is no evidence of tumor outside the posterior fossa.Electron beam radiation of the spinal component can decrease the dose to some of the normal structures and prevent some of the long-term sequelae.

Cerebellar Neoplasms↗