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Title: Radiation Therapy of Large Intact Breasts Using a Beam Spoiler or Photons with Mixed Energies

Abstract

Radiation treatment of large intact breasts with separations of more than 24 cm is typically performed using x-rays with energies of 10 MV and higher, to eliminate high-dose regions in tissue. The disadvantage of the higher energy beams is the reduced dose to superficial tissue in the buildup region. We evaluated 2 methods of avoiding this underdosage: (1) a beam spoiler: 1.7-cm-thick Lucite plate positioned in the blocking tray 35 cm from the isocenter, with 15-MV x-rays; and (2) combining 6- and 15-MV x-rays through the same portal. For the beam with the spoiler, we measured the dose distribution for normal and oblique incidence using a film and ion chamber in polystyrene, as well as a scanning diode in a water tank. In the mixed-energy approach, we calculated the dose distributions in the buildup region for different proportions of 6- and 15-MV beams. The dose enhancement due to the beam spoiler exhibited significant dependence upon the source-to-skin distance (SSD), field size, and the angle of incidence. In the center of a 20 x 20-cm{sup 2} field at 90-cm SSD, the beam spoiler raises the dose at 5-mm depth from 77% to 87% of the prescription, while maintaining the skin dosemore » below 57%. Comparison of calculated dose with measurements suggested a practical way of treatment planning with the spoiler-usage of 2-mm 'beam' bolus-a special option offered by in-house treatment planning system. A second method of increasing buildup doses is to mix 6- and 15-MV beams. For example, in the case of a parallel-opposed irradiation of a 27-cm-thick phantom, dose to D{sub max} for each energy, with respect to midplane, is 114% for pure 6-, 107% for 15-MV beam with the spoiler, and 108% for a 3:1 mixture of 15- and 6-MV beams. Both methods are practical for radiation therapy of large intact breasts.« less

Authors:
 [1];  [2];  [3];  [2]
  1. Department of Radiation Oncology, Mount Sinai School of Medicine, New York, NY (United States), E-mail: ELief@cristhospital.org
  2. Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY (United States)
  3. Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY (United States)
Publication Date:
OSTI Identifier:
21045979
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Dosimetry; Journal Volume: 32; Journal Issue: 4; Other Information: DOI: 10.1016/j.meddos.2007.02.002; PII: S0958-3947(07)00046-5; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; BEAMS; INCIDENCE ANGLE; IONIZATION CHAMBERS; LUCITE; MAMMARY GLANDS; NEOPLASMS; PLANNING; POLYSTYRENE; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; RADIOTHERAPY; SKIN; X RADIATION

Citation Formats

Lief, Eugene P., Hunt, Margie A., Hong, Linda X., and Amols, Howard I. Radiation Therapy of Large Intact Breasts Using a Beam Spoiler or Photons with Mixed Energies. United States: N. p., 2007. Web. doi:10.1016/j.meddos.2007.02.002.
Lief, Eugene P., Hunt, Margie A., Hong, Linda X., & Amols, Howard I. Radiation Therapy of Large Intact Breasts Using a Beam Spoiler or Photons with Mixed Energies. United States. doi:10.1016/j.meddos.2007.02.002.
Lief, Eugene P., Hunt, Margie A., Hong, Linda X., and Amols, Howard I. Mon . "Radiation Therapy of Large Intact Breasts Using a Beam Spoiler or Photons with Mixed Energies". United States. doi:10.1016/j.meddos.2007.02.002.
@article{osti_21045979,
title = {Radiation Therapy of Large Intact Breasts Using a Beam Spoiler or Photons with Mixed Energies},
author = {Lief, Eugene P. and Hunt, Margie A. and Hong, Linda X. and Amols, Howard I.},
abstractNote = {Radiation treatment of large intact breasts with separations of more than 24 cm is typically performed using x-rays with energies of 10 MV and higher, to eliminate high-dose regions in tissue. The disadvantage of the higher energy beams is the reduced dose to superficial tissue in the buildup region. We evaluated 2 methods of avoiding this underdosage: (1) a beam spoiler: 1.7-cm-thick Lucite plate positioned in the blocking tray 35 cm from the isocenter, with 15-MV x-rays; and (2) combining 6- and 15-MV x-rays through the same portal. For the beam with the spoiler, we measured the dose distribution for normal and oblique incidence using a film and ion chamber in polystyrene, as well as a scanning diode in a water tank. In the mixed-energy approach, we calculated the dose distributions in the buildup region for different proportions of 6- and 15-MV beams. The dose enhancement due to the beam spoiler exhibited significant dependence upon the source-to-skin distance (SSD), field size, and the angle of incidence. In the center of a 20 x 20-cm{sup 2} field at 90-cm SSD, the beam spoiler raises the dose at 5-mm depth from 77% to 87% of the prescription, while maintaining the skin dose below 57%. Comparison of calculated dose with measurements suggested a practical way of treatment planning with the spoiler-usage of 2-mm 'beam' bolus-a special option offered by in-house treatment planning system. A second method of increasing buildup doses is to mix 6- and 15-MV beams. For example, in the case of a parallel-opposed irradiation of a 27-cm-thick phantom, dose to D{sub max} for each energy, with respect to midplane, is 114% for pure 6-, 107% for 15-MV beam with the spoiler, and 108% for a 3:1 mixture of 15- and 6-MV beams. Both methods are practical for radiation therapy of large intact breasts.},
doi = {10.1016/j.meddos.2007.02.002},
journal = {Medical Dosimetry},
number = 4,
volume = 32,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}