Biomedical subjects

S Nag

Publications and source records attributed to S Nag.

169 records · Page 10Linked to original sources

PubMedDate not supplied

The American Brachytherapy Society perspective on intravascular brachytherapy.

BACKGROUND: Recent clinical studies indicate that intravascular brachytherapy (IVB) can reduce the rate of restenosis substantially after angioplasty procedures. However, no clinical guidelines exist for optimal therapy. METHODS: The members of the IVB Subcommittee of the American Brachytherapy Society (ABS) identified the areas of consensus and controversies in IVB to issue the ABS perspective on IVB, based on analysis of published reports and the clinical experience of the members in brachytherapy. RESULTS: IVB is still experimental. The long-term efficacy, toxicity, the target tissue, and dose required for IVB are not established. The ABS recommends that IVB procedures must be performed, with careful attention to radiation-related issues, in the context of controlled multidisciplinary clinical trials with the approval of the institutional review board, the Nuclear Regulatory Commission, the Food and Drug Administration, and under an Investigational Device Exemption. The therapeutic radiologist, with a qualified radiation physicist, is responsible for dose prescription and delivery and needs to be present during the IVB procedure as part of this multidisciplinary team. The long-term outcome from these studies should be reviewed critically and published in peer-reviewed journals. The ABS endorsed the dosimetric guidelines of the American Association of Physicists in Medicine Task Group 60 (AAPM TG-60) report. The ABS recommends that dose specification be defined clearly; to allow comparisons between studies, the dose should be prescribed at 2 mm from the source for intracoronary brachytherapy and at an average luminal radius of +2 mm for peripheral vascular brachytherapy. The prescription doses at the above point is generally in the 12-18 Gy range. Comprehensive procedures for quality assurance, radiation protection, and emergencies should be in place before initiating an IVB program. Higher energy beta sources, lower energy gamma sources, dose-volume histograms, and correlation of three-dimensional reconstructions of delivered dose with patterns of failure are areas for further research. CONCLUSION: The ABS perspective on IVB is presented to assist the interventional team in developing protocols for the use of IVB in the prevention of restenosis. Long-term outcome data with a standardized reporting system are needed to establish the role of brachytherapy in preventing vascular restenosis. Endovascular brachytherapy is a new and evolving modality, and these recommendations are subject to modifications as new data become available.

Brachytherapy↗

PubMedDate not supplied

Brachytherapy for the interventional cardiologist and vascular surgeon.

PURPOSE: There has been recent interest in the use of brachytherapy for the possible prevention of restenosis after angioplasty. However, this field is unfamiliar to most interventional cardiologists. This article is meant to serve as an introduction to the principles of brachytherapy especially as it applies to intravascular brachytherapy. Because the intended audience is the interventional cardiologist, the details of physics, radiobiology, and radiation jargon has been kept at a minimum. METHODS: The main advantages of brachytherapy are that it can irradiate small volumes and conform to the target volume while sparing the surrounding normal tissues from the deleterious effects of irradiation. Various gamma- or beta-emitting radioisotopes can deliver the brachytherapy dose. In general, the beta emitters have fewer radiation exposure hazards, but the limited penetration of beta emitters can be a problem if deeper tissues need to be irradiated. Gamma sources can irradiate deeper but suffer from greater radiation exposure hazards. It should be remembered that the biological effects of radiation depend on a number of parameters, including the radiation modality, dose, dose rate, fractionation, treatment duration, dose prescription point, and the volume irradiated. The use of low energy isotopes, beta emitters, and remote-controlled afterloading has reduced the radiation exposure to the medical caregivers. CONCLUSION: Intravascular brachytherapy is currently considered to be experimental. Those wishing to start a new intravascular brachytherapy program should comply with the required federal and state regulatory guidelines issued by the Nuclear Regulatory Commission, Food and Drug Administration, and their individual Institutional Review Board.

Brachytherapy↗

PubMedDate not supplied

Technique for construction of dental molds for high-dose-rate remote brachytherapy.

High-dose-rate remote (HDR) brachytherapy eliminates radiation exposure hazard to personnel, allows for optimum dosage planning (dosimetry), and delivers high radiation dose close to the tumor in only a few minutes. The catheters can be incorporated into a fixed geometry within a mold, allowing for repeated treatments without the need for repeated implantation of radioactive isotopes or repeated dosimetry. This article presents the use of HDR brachytherapy in three patients to illustrate the advantages of HDR brachytherapy for the treatment of head and neck cancers in the following circumstances: (a) for outpatient therapy, (b) as an addition to or potentiation of external beam irradiation, (c) for preservation of function of regional structures, (d) for optimization of dosimetry, and (e) for palliation. It requires close interaction among the radiation oncologist, head and neck surgeon, and the dental oncologist and/or maxillofacial prosthodontist in order for optimum benefit for the patient to be achieved.

Acrylic Resins↗

PubMedDate not supplied

Gestational variation of glycerophosphate acyltransferase activity in maternal guinea pig lung and possible role of thyroid hormone in its de novo synthesis.

We have observed earlier that the pattern of gestational variation of microsomal glycerophosphate acyltransferase (GAT) activity is similar in maternal and fetal guinea pig lung. Furthermore, there is a close resemblance between these patterns and that of the gestational variation of fetal plasma thyroid hormone. It is known that triiodothyronine (T3) injected to pregnant rats can cross the placenta to some extent and cause an increase in phosphatidylcholine synthesis in fetal lung. It is possible, therefore, that the gestational increase of GAT activity in maternal and fetal lung is associated with an increase in maternal plasma thyroid hormone. The objective of this study was to investigate whether intramuscular injection of T3 to adult guinea pig causes any change in the activity of GAT in lung and, if so, to determine the mechanistic basis. The results indicated that T3 significantly increased the GAT activity in the microsomes but not in the mitochondria. Actinomycin D or cycloheximide abolished the hormone-mediated stimulation of the enzyme in the microsomes, suggesting that T3 is involved in both transcriptional and translational pathways of GAT synthesis. We also confirmed our previous preliminary finding that there is a gestational variation of GAT activity in maternal guinea pig lung and furthermore the increase in GAT activity during pregnancy is predominantly in the microsomes.

Animals↗

PubMedDate not supplied

Use of combined intraoperative radiotherapy and 125I brachytherapy in incompletely resected recurrent colorectal carcinoma.

This technique paper describes a new treatment strategy which involves the combination of 125I brachytherapy and intraoperative radiotherapy (IOERT) in the treatment of recurrent colorectal adenocarcinoma. IOERT is used to encompass the areas of presumed microscopic disease with the IOERT dose being kept below the threshold for severe neuropathy. Brachytherapy with 125I is used to boost areas of gross disease within the IOERT treated area that would otherwise require potentially neurotoxic IOERT doses to achieve local control. The outcome results of patients treated with this technique will be reported at a later date after further patient actual and longer follow-up.

Brachytherapy↗

PubMedDate not supplied

Intraoperative high dose rate brachytherapy can be used to salvage patients with previously irradiated head and neck recurrences.

PURPOSE: To develop a novel technique, intraoperative high-dose rate brachytherapy (IOHDR), in the treatment of previously irradiated head and neck cancers located at anatomical sites inaccessible to intraoperative electron beam radiotherapy (IOERT). METHODS: Between October 1992 and June 1997, seven patients (median age = 65 yrs; range = 52 to 71 years) with previously irradiated head and neck recurrences at anatomical sites inaccessible to IOERT in the base of skull were treated with IOHDR after maximal resection for microscopic residual disease. Treatment volume ranged from 6 cc to 24 cc. Six patients received 15 Gy of IOHDR at 0.5 cm; one received 10 Gy using custom-made surface foam applicators. RESULTS: The median follow-up was 59 months (range 33 to 67 months). It was technically feasible to deliver IOHDR in all seven patients at sites that were inaccessible to IOERT. The morbidity (observed in two patients) was acceptable and generally surgically related. Four of seven patients (57%) were locally controlled at IOHDR site. Two failed regionally, outside the IOHDR treated sites. The disease-free survival ranged from 3 to 30 months (median 9 months) with two patients still alive, disease-free at 28 and 30 months. CONCLUSIONS: IOHDR can be used, with limited toxicity, to treat previously irradiated head and neck cancers at sites inaccessible to IOERT. We are currently evaluating the addition of limited EBRT dose to improve the local control of these poor prognosis recurrent tumors.

Aged↗

PubMedDate not supplied

Augmentation of luteinizing hormone action by prostaglandin E2 in the prevention of antispermatogenic effect of indomethacin. Indomethacin & spermatogenesis.

Administration of indomethacin exhibited antigonadal action by inhibiting the Leydig cells, sex-accessories and spermatocyte-spermatid conversion process. Administration of PGE2 or PGF2 alpha had no effect on Leydig cell nuclear volume or accessory organ weights, but PGE2 had a restorative effect on the efficiency of meiosis, although at a statistical non-significant level. Administration of LH to indomethacin treated rats restored the accessories fully with a non-significant effect on the yield of step-7 spermatids from meiosis. Simultaneous administration of indomethacin, LH and PGE2 (but not PGF2 alpha) restored both sex-accessories and spermatid number to the level of vehicle injected controls.

Animals↗