The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Howard I Amols - One of the best experts on this subject based on the ideXlab platform.
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Photoneutrons from medical linear accelerators radiobiological measurements and risk estimates
International Journal of Radiation Oncology Biology Physics, 1995Co-Authors: Eric J. Hall, Howard I Amols, Stewart G. Martin, Tom K. HeiAbstract:Purpose: To assess the oncogenic potential of the Photoneutrons produced by high energy medical linear accelerators. Methods and Materials: An established line of cells of rodent origin (C$I lOTlI2) was used to assess the oncogenic potential of the radiation dose received in the breast of an anthropomorphic “randoman” phanton, while the cervix received a dose of 70 Gy. Experiments were performed at 6 MV, below the threshold for the production of Photoneutrons, and at 20 MV where the dose includes about 0.01 Gy of Photoneutrons as well as scattered x-rays. Results: A significantly higher transformation incidence was observed for the 20-MV machine, consistent withe measured neutron dose of about 0.01 Gy and a quality factor of 20. Conclusion: An estimate can be made of the additional deaths from second malignancies that might result from the Photoneutrons generated by higher energy linear accelerators (Linacs), which must be offset against the possible improvements in survival that might result from the higher tumor doses made possible by the increased percentage depth doses. Photoneutrons, Second malignancies, Linear accelerators.
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Photoneutrons from medical linear accelerators—Radiobiological measurements and risk estimates
International journal of radiation oncology biology physics, 1995Co-Authors: Eric J. Hall, Howard I Amols, Stewart G. Martin, Tom K. HeiAbstract:Purpose: To assess the oncogenic potential of the Photoneutrons produced by high energy medical linear accelerators. Methods and Materials: An established line of cells of rodent origin (C$I lOTlI2) was used to assess the oncogenic potential of the radiation dose received in the breast of an anthropomorphic “randoman” phanton, while the cervix received a dose of 70 Gy. Experiments were performed at 6 MV, below the threshold for the production of Photoneutrons, and at 20 MV where the dose includes about 0.01 Gy of Photoneutrons as well as scattered x-rays. Results: A significantly higher transformation incidence was observed for the 20-MV machine, consistent withe measured neutron dose of about 0.01 Gy and a quality factor of 20. Conclusion: An estimate can be made of the additional deaths from second malignancies that might result from the Photoneutrons generated by higher energy linear accelerators (Linacs), which must be offset against the possible improvements in survival that might result from the higher tumor doses made possible by the increased percentage depth doses. Photoneutrons, Second malignancies, Linear accelerators.
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Photoneutrons from high energy medical linear accelerators measurement of the spectrum and dose using a miniature proportional counter
International Journal of Radiation Oncology Biology Physics, 1995Co-Authors: Paul Kliauga, Howard I AmolsAbstract:PURPOSE A new method of measuring photoneutron dose to the patient during treatment with high energy photon or electron beams is presented. This method has the advantage of providing not only the dose, but the microdosimetric spectrum at the same time. METHODS AND MATERIALS A miniature cylindrical gas proportional counter (0.5 mm diameter by 0.5 mm height) has been used to measure scatter radiation from a 20 MV teletherapy photon beam. At atmospheric pressure, filled with propane base tissue equivalent gas, this counter simulates a unit density tissue region of approximately 0.9 microns. We present here single event microdosimetric spectra measured outside the primary beam 1.4 m from the target. This technique allows a single measurement to determine the scattered dose due to gammas and photoneutron contamination, as well as the quality factor of the Photoneutrons. RESULTS Spectral components from scattered photons and the Photoneutrons are easily separated, and dose contributions can be estimated. The ratio of photoneutron dose measured by the proportional counter to photon dose at isocenter is 0.75 x 10(-4). CONCLUSIONS Neutron dose was also measured using a bubble neutrometer. The proportional counter and neutrometer agree within experimental errors. This type of instrument is shown to be a viable technique for determination of exposure of patient and also personnel to Photoneutrons, providing not only a dose determination, but also a spectrum that can be used to estimate quality factors for equivalent dose. Its main drawback is that it requires a lengthy (several hours) measurement because of low count rate of the neutrons.
Tom K. Hei - One of the best experts on this subject based on the ideXlab platform.
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Photoneutrons from medical linear accelerators—Radiobiological measurements and risk estimates
International journal of radiation oncology biology physics, 1995Co-Authors: Eric J. Hall, Howard I Amols, Stewart G. Martin, Tom K. HeiAbstract:Purpose: To assess the oncogenic potential of the Photoneutrons produced by high energy medical linear accelerators. Methods and Materials: An established line of cells of rodent origin (C$I lOTlI2) was used to assess the oncogenic potential of the radiation dose received in the breast of an anthropomorphic “randoman” phanton, while the cervix received a dose of 70 Gy. Experiments were performed at 6 MV, below the threshold for the production of Photoneutrons, and at 20 MV where the dose includes about 0.01 Gy of Photoneutrons as well as scattered x-rays. Results: A significantly higher transformation incidence was observed for the 20-MV machine, consistent withe measured neutron dose of about 0.01 Gy and a quality factor of 20. Conclusion: An estimate can be made of the additional deaths from second malignancies that might result from the Photoneutrons generated by higher energy linear accelerators (Linacs), which must be offset against the possible improvements in survival that might result from the higher tumor doses made possible by the increased percentage depth doses. Photoneutrons, Second malignancies, Linear accelerators.
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Photoneutrons from medical linear accelerators radiobiological measurements and risk estimates
International Journal of Radiation Oncology Biology Physics, 1995Co-Authors: Eric J. Hall, Howard I Amols, Stewart G. Martin, Tom K. HeiAbstract:Purpose: To assess the oncogenic potential of the Photoneutrons produced by high energy medical linear accelerators. Methods and Materials: An established line of cells of rodent origin (C$I lOTlI2) was used to assess the oncogenic potential of the radiation dose received in the breast of an anthropomorphic “randoman” phanton, while the cervix received a dose of 70 Gy. Experiments were performed at 6 MV, below the threshold for the production of Photoneutrons, and at 20 MV where the dose includes about 0.01 Gy of Photoneutrons as well as scattered x-rays. Results: A significantly higher transformation incidence was observed for the 20-MV machine, consistent withe measured neutron dose of about 0.01 Gy and a quality factor of 20. Conclusion: An estimate can be made of the additional deaths from second malignancies that might result from the Photoneutrons generated by higher energy linear accelerators (Linacs), which must be offset against the possible improvements in survival that might result from the higher tumor doses made possible by the increased percentage depth doses. Photoneutrons, Second malignancies, Linear accelerators.
Eric J. Hall - One of the best experts on this subject based on the ideXlab platform.
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Photoneutrons from medical linear accelerators—Radiobiological measurements and risk estimates
International journal of radiation oncology biology physics, 1995Co-Authors: Eric J. Hall, Howard I Amols, Stewart G. Martin, Tom K. HeiAbstract:Purpose: To assess the oncogenic potential of the Photoneutrons produced by high energy medical linear accelerators. Methods and Materials: An established line of cells of rodent origin (C$I lOTlI2) was used to assess the oncogenic potential of the radiation dose received in the breast of an anthropomorphic “randoman” phanton, while the cervix received a dose of 70 Gy. Experiments were performed at 6 MV, below the threshold for the production of Photoneutrons, and at 20 MV where the dose includes about 0.01 Gy of Photoneutrons as well as scattered x-rays. Results: A significantly higher transformation incidence was observed for the 20-MV machine, consistent withe measured neutron dose of about 0.01 Gy and a quality factor of 20. Conclusion: An estimate can be made of the additional deaths from second malignancies that might result from the Photoneutrons generated by higher energy linear accelerators (Linacs), which must be offset against the possible improvements in survival that might result from the higher tumor doses made possible by the increased percentage depth doses. Photoneutrons, Second malignancies, Linear accelerators.
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Photoneutrons from medical linear accelerators radiobiological measurements and risk estimates
International Journal of Radiation Oncology Biology Physics, 1995Co-Authors: Eric J. Hall, Howard I Amols, Stewart G. Martin, Tom K. HeiAbstract:Purpose: To assess the oncogenic potential of the Photoneutrons produced by high energy medical linear accelerators. Methods and Materials: An established line of cells of rodent origin (C$I lOTlI2) was used to assess the oncogenic potential of the radiation dose received in the breast of an anthropomorphic “randoman” phanton, while the cervix received a dose of 70 Gy. Experiments were performed at 6 MV, below the threshold for the production of Photoneutrons, and at 20 MV where the dose includes about 0.01 Gy of Photoneutrons as well as scattered x-rays. Results: A significantly higher transformation incidence was observed for the 20-MV machine, consistent withe measured neutron dose of about 0.01 Gy and a quality factor of 20. Conclusion: An estimate can be made of the additional deaths from second malignancies that might result from the Photoneutrons generated by higher energy linear accelerators (Linacs), which must be offset against the possible improvements in survival that might result from the higher tumor doses made possible by the increased percentage depth doses. Photoneutrons, Second malignancies, Linear accelerators.
Hashemi Dizaji Seyed Mehdi - One of the best experts on this subject based on the ideXlab platform.
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Effect of PMMA shield on photoneutron dose equivalent in high energy medical linacs
Physica Medica, 2016Co-Authors: Hashemi Dizaji Seyed MehdiAbstract:High energy photon beams from medical linacs produce, besides the clinically useful photon beams, secondary neutrons. These Photoneutrons increase patient dose and may cause secondary malignancies. The effect of PMMA shield on reduction of photoneutron dose equivalent produced by a high energy medical linac is investigated in this study. To determine the photoneutron dose equivalent by a Varian linac working at 18 MV photonmode, Polycarbonate films was used. Measurements done at distances 0, 10, 20, 50 cm from the center of the X-ray beam for open field and after inserting 1 cm thick PMMA shield in the X-ray field. After electrochemical etching of the PC films, the neutron dose equivalent was calculated. The results show that by increasing the distance from the center of the X-ray beam towards the periphery, the photoneutron dose equivalent decreases rapidly for both the open and shielded fields and that by inserting the PMMA shield in the path of the X-ray beam, the photoneutron dose equivalent was decreased obviously compared to open field. Results show a PMMA shield, can significantly reduce photoneutron dose equivalent at patient plane. Although, same amount of X-ray (100 MU) is provided by linac in both shielded and open fields, it can be seen that using the shield causes a considerable decrease in photoneutron dose equivalent (p
Jai Ki Lee - One of the best experts on this subject based on the ideXlab platform.
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Assessment and Measurement of the Photoneutron Field Produced in the Varian Medical Linear Accelerator
Journal of Nuclear Science and Technology, 2007Co-Authors: Hong Suk Kim, Jai Ki LeeAbstract:This paper evaluates the doses and spectra of Photoneutrons produced in a medical linear accelerator with photon energies of 10 and 15 MV. The Monte Carlo code, MCNPX, was used to simulate the transport of these Photoneutrons in the plane of a patient and around the upper part of the head. The fully described geometry of the varian accelerator head was used in this calculation. The photoneutron energy spectra and doses for various photon field sizes were calculated at 20 positions for each field. The results indicate that the maximum dose equivalents are observed in the 20 × 20 cm2 photon field size. It was found that the average neutron energy at the isocenter for a 0 × 0 cm2 field is 0.38 MeV for 10 MV and 0.45 MeV for 15 MV. The neutron doses at 10 positions around the head in the treatment room of the operation facilities with energies of 10 and 15 MV were measured using bubble detectors. Measurements were compared with the calculations using the same geometry in the experiment. It was found that the ...