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Biomedical subjects

N Suntharalingam

Publications and source records attributed to N Suntharalingam.

At least 37 records · Page 2Linked to original sources

Dosimetric characteristics of a 6 MV photon beam from a linear accelerator with asymmetric collimator jaws.

Dosimetric measurements have been made of a 6 MV photon beam from a linear accelerator equipped with asymmetric jaws. The field size factors for asymmetrically set fields are compared to those for symmetrically set fields. The change of beam quality has been measured as a function of off-axis position of the asymmetric fields to assess its effect on depth dose. Additional measurements include beam penumbra and shape of isodose curves for open and wedge fields as the field opening is moved asymmetrically from the central ray.

Particle Accelerators↗

Radiation oncology. Programs for the present and future.

Radiation oncology in 1984 continues to make major advances in the multidisciplinary clinical programs. This has been possible by virtue of the radiation oncologist, who is an active participant in these clinical programs. The changing role for the radiation oncologist has dictated a greater participation in the primary management of the patient's disease process and also participation in multidisciplinary research programs.

Breast Neoplasms↗

Quality assurance in radiation therapy: future plans in physics.

Modern day radiation therapy has seen the impact of high technology resulting in more sophisticated computer augmented treatment delivery systems, treatment planning procedures and diagnostic imaging techniques. Much work has already been reported in the area of physics efforts related to quality assurance in radiation therapy. Future efforts in physics will have to address the new developments in each component of the whole radiation treatment process. Certain new developments, using both computer and imaging technologies, show promise in providing tools to verify the accuracy of the delivered radiation treatment. Areas receiving careful attention are: integration and registration of information from multiple sources of diagnostic studies; validation of the accuracy of treatment planning systems; assessment of relative merits of alternate dose distributions; improvement of portal and verification film image quality; real time monitoring using light emitting screens and coupled with TV systems; monitoring of treatment and machine parameters using "record and verify" computer systems. The medical physics community, primarily through the American Association of Physicists in Medicine (AAPM), will continue the development of methodologies for technology transfer in the area of quality assurance. Committees and task groups within the AAPM will address the new developments impacting on quality assurance and prepare appropriate protocols and documents to assist the practicing physicist. By necessity, the national Radiological Physics Center (RPC) and the regional Centers for Radiological Physics (CRP) will have to take a major role in the development of new quality assurance programs.

Humans↗

Medical radiation dosimetry.

Current dose measuring practices in the diagnostic and therapeutic use of radiation are reviewed. Radiation doses typically received by patients from diagnostic X-ray studies, including mammography and computerized axial tomography, are presented. Modern-day radiation therapy, both with conventional photons and with electrons and high-LET particles, emphasizes the need for accurate dosimetry. The different methods of beam calibration and dosimetry intercomparisons for the variety of radiation beams are discussed. Results of several important dosimetry intercomparisons are also presented.

Electrons↗

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↗

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↗

Pancreatic carcinoma treated with high-dose, small-volume irradiation.

Eighteen patients with unresectable ductal adenocarcinoma of the pancreas received definitive, high-dose, small-volume radiation therapy. All patients had at least one laparotomy, at which time a biopsy was obtained, radio-opaque clips were placed to define the extent of the gross tumor, and usually some form of bypass procedure was performed. External-beam irradiation was delivered from a 45-MV betatron to an area encompassing the clipped tumor volume plus a 1 to 2 cm margin. A three-field technique, employing opposed lateral 45-MV photon beams and an anterior "mixed beam" (50% 45-MV photons and 50% 15- to 35-MeV electrons), was used to treat 13 of the patients. The choice of electron energy used for these patients was based on the depth of the posterior margin of the target volume. Five patients were treated by either four-field "box" or three-field, 45-MV photon techniques. Minimum tumor dose was 6300-6700 rads delivered in 180-rad fractions in 7-9 weeks. With the three-field technique, all fields were treated daily; with the four-field technique, two fields were treated daily. The projected survival rate 12 months post idagnosis is 59%, with the median length of survival, 11.8 months. Seven patients are alive 11.5 to 57 months after diagnosis, all clinically free of disease. Treatment has been generally well tolerated, and there have been no severe late radiation complications. This therapeutic modality appears capable of producing improved palliation, if not offering definitive radiotherapeutic management of localized unresectable carcinoma of the pancreas.

Adenocarcinoma↗

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↗