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Biomedical subjects

K Ayyangar

Publications and source records attributed to K Ayyangar.

At least 19 recordsLinked to original sources
PubMed1995

Potential underdosing with the use of electron beam therapy in patients with cervical adenopathy and advanced head and neck cancer.

To define the adequacy of electron beam therapy in the treatment of N1-N3 head and neck cancer, 24 patients with primary head and neck cancers and N1-N3 cervical adenopathy received primary radiation therapy with or without chemotherapy for definitive control of their disease. All patients underwent computerized tomography (CT) to assist in the design of treatment to the posterior neck with electron beams after photon therapy to the level of spinal cord tolerance. Treatment with electrons to the posterior neck in patients with N1 disease was adequate in 92% (11/12) of patients. However, in patients with N2 and N3 disease, electron beam treatment failed, because of spinal cord tolerance problems, to cover the disease adequately in 92% (11/12). It is concluded that CT should be employed routinely in patients with N1-N3 neck disease to determine the proper electron energy prescription. For some patients, electron beam may not be appropriate, making it necessary to use individual planning to treat adequately the neck disease and avoid the spinal cord.

Electrons↗
PubMed1995

3-D reconstruction of Ir-192 implant dosimetry for irradiating gingival carcinoma on the mandibular alveolar ridge.

A recurrent cancer in the gingiva has been treated by specially fabricating a dental acrylic appliance. This replica of the floor of the mouth, gums, and teeth was constructed with the use of a vinyl polysiloxine impression material. The tumor boundaries were marked in the fabricated appliance with four metal wires to localize the surface and periphery of the tumor. The appliance was molded to hold Ir-192 wires in near contact with the target surface and to allow afterloading. A specially designed lead shield was imbedded onto the dorsal surface of the appliance so as to reduce dose to the tongue and maxillary structures of the mouth. Simulation films and 3-D treatment planning were used to generate isodose distributions and to allow preplanning. The dose calculation algorithm was modified to account for the attenuation in the lead shield represented in three dimensions. The Ir-192 mold was successfully applied for 38 hours in two sessions 1 week apart.

Aged↗
PubMed1995

Verification of water equivalence of FeMRI gels using Monte Carlo simulation.

Dosimetric characteristics of the FeMRI gels for various energy photon and electron beams were investigated using the Integrated Tiger Series (ITS) Monte Carlo codes. The FeMRI gels have been reported as being tissue-substitutes which can be shaped to any desired contour for three-dimensional (3D) mapping of dose distribution using magnetic resonance (MR) scanning. This study indicated that the central axis depth dose, off-axis depth dose, transverse profile at the depth of 50% of maximum dose, and energy deposition for photons and electrons in the gels are close to those in water. From these comparisons, it is concluded that FeMRI gels are suitable substitutes for water for the purposes of dose measurements of both photons and electrons used in radiotherapy.

Electrons↗
PubMed1994

Automatic field shaping for conformal radiation therapy.

A computer method has been developed to shape the radiation field to conform to the shape of the target as visualized through the beam's eye view (BEV) perspective for conformal radiation therapy. Initially, a series of 2D target contours to define the target size are input into the computer. These target contour data are mapped onto a 3D surface and thereafter projected onto a BEV plane. The projection's outer boundary of the target is auto-contoured. After auto-contouring, a margin is automatically added to define the radiation beam cross section. Since the BEV plane is arbitrarily oriented about the target, the beam orientation can be non-coplanar to the plane of the target contours. For a chosen beam orientation, the conformal treatment beam cross section can be generated automatically using this computer technique and output to either a laser printer, a plotter or stored on files for transfer to the linear accelerator computer system.

Humans↗
PubMed1994

Potential underdosing with the use of electron-beam therapy in patients with cervical adenopathy and advanced head and neck cancer.

To define the adequacy of electron-beam therapy in the treatment of N1-N3 head and neck cancer, 24 patients with primary head and neck cancers and N1-N3 cervical adenopathy received primary radiation therapy with or without chemotherapy for definitive control of their disease. All patients underwent computerized tomography (CT) to assist in the design of treatment to the posterior neck with electron beams after photon therapy to the level of spinal cord tolerance. Treatment with electrons to the posterior neck in patients with N1 disease was adequate in 92% (11/12) of patients. However, in patients with N2/N3 disease, electron beam failed, because of spinal-cord tolerance problems, to adequately cover disease in 92% (11/12). It is concluded that CT should be routinely employed in patients with N1-N3 neck disease to determine the proper electron-energy prescription. For some patients, electron beam may not be appropriate, making it necessary to use individual planning to treat adequately the neck disease and avoid the spinal cord.

Electrons↗
PubMed1993

Application of magnetic resonance imaging and three-dimensional treatment planning in the treatment of orbital lymphoma.

Radiotherapy for lymphoma of the orbit must be individualized for each patient and clinical setting. Most techniques focus on optimizing the dose to the tumor while sparing the lens. This study describes a technique utilizing magnetic resonance imaging (MRI) and three dimensional (3D) planning in the treatment of orbital lymphoma. A patient presented with an intermediate grade lymphoma of the right orbit. The prescribed tumor dose was 4050 cGy in 18 fractions. Three D planning was carried out and tumor volumes, retina, and lens were subsequently outlined. Dose calculations including dose volume histograms of the target, retina, and lens were then performed. Part of the retina was outside of the treatment volume while 50% of the retina received 90% or more of the prescribed dose. The patient was clinically NED when last seen 2 years following therapy with no treatment-related morbidity. Patients with lymphomas of the orbit can be optimally treated using MRI based 3D treatment planning.

Aged↗
PubMed1990

Comparison of lymphangiography and computed tomography scanning in evaluating abdominal disease in stages III and IV Hodgkin's disease. A Southwest Oncology Group study.

The authors reviewed the records of 139 patients who had laparotomy plus computed tomography (CT) and/or lymphangiograms (LAG) as part of a their staging workup for Hodgkin's disease, in accordance with Southwest Oncology Group (SWOG) protocol 7808. They evaluated the relative ability of CT and LAG to detect disease in the abdomen. Two regions of the abdomen were designated, the upper and the lower, to further examine the capabilities of CT and LAG in the lower abdomen and CT in the upper abdomen. A LAG was more sensitive (P less than 0.05) than CT in detecting positive lower abdominal nodes. In the upper abdomen, CT scan had low sensitivity for detecting positive nodes, liver, or spleen. This study suggests that LAG of the lower abdomen provided more information than CT, and therefore should not be abandoned as a valid method for detecting nodal disease.

Abdomen↗
PubMed1979

Betatron electron beam characterisation for dosimetry calculations.

Parameters have been specified for electron beams with energies 5--45 MeV from a Brown Boveri betatron for use in computerised dosimetry calculations. A semi-empirical equation is given for the dose at any point at various depths in water. This equation is a modification to Kawachi's predictive model which was based on solutions of a general age--diffusion equation. The depth doses and isodose curves are predicted as a function of the practical range, source skin distance (SSD) and field size. Depth dose accuracy requirements of +/-2% above 50% depth dose and +/-5% at lower doses, relative to maximum dose, have been set and achieved. Also, the shape of the isodose curves with the constrictions at higher doses and bulging at lower values are accurately predicted. Computer calculated beams have been used to generate summed isodose distributions for certain clinical situations.

Computers↗
PubMed1979

Comparison of various radiation techniques in treatment of the breast and chest wall.

Radiation therapy will continue to play a major role in the curative management of patients with mammary carcinoma. For this reason, a comparison was made of the dose distributions and techniques used by several leading institutions in the treatment of the chest wall and internal mammary nodes. The dose distributions within the treatment volumes were similar. However, some unique differences within the treatment volume, as well as in the skin and superficial tissues were found.

Breast Neoplasms↗
PubMed1976

Ultraviolet response of CaSO4:Dy.

A simple method for measuring ultraviolet exposure using the thermoluminescent properties of CaSO4:Dy is presented in this paper. In general, three peaks at 145, 215 and 365 degrees C were observed by ultraviolet irradiation of virgin phosphor. The peak at 365 degrees C was found to be very small and that at 145 degrees C fades away within a week; no appreciable fading was observed for the 215 degrees C peak. Further, the peak at 215 degrees C was found to coincide with the gamma dosimetric peak and this peak was chosen for ultraviolet exposure measurements. A standard quartz pen-ray lamp was used for calibrating the phosphor both by peak height measurement and by integration. The dosimetric peak has been found to be linear from the detection threshold of 400 erg mm-2 to 4 X 10(4) erg mm-2. Beyond this exposure the phosphor behaved supralinearly to ultraviolet exposure up to the studied range of 5 X 10(5) erg mm-2. The phosphor exhibited strong dependence on photon energy. The TL sensitivity increases sharply by a factor of 300 as the wavelength is decreased from 250 to 200 nm. The response is negligibly small above 350 nm. Other important characteristics such as particle size dependence, fading characteristics, thickness dependence and re-usability are also presented. The ultraviolet sensitivity increased by a factor of 3 when the grain size range was changed from 105-210 mum. Self-shielding by a factor of 2 was observed when the sample thickness was increased from 10 to 72 mg cm-2.

Calcium↗
PubMed1976

Clinical and dosimetric considerations in the radiation treatment of breast cancer.

Preliminary results indicate that film dosimetry is a simple and precise method of determining volume dose distributions. Calculated dose distributions using computers or estimations of surface dose using TLD dosimeters are within 5% of the measured dose. Initial attempts to find suitable alternate techniques tailored to each clinical situation are encouraging.

Breast Neoplasms↗