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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}
}
  • Radiation complications are often related to the dose inhomogeneity (hot spot) in breast tissue treated with conservative therapy, especially for large patients. The effect of photon energy on radiation dose distribution is analyzed to provide guidelines for the selection of beam energy when tangential fields and limited slices are used to treat women with large breasts. Forty-eight patients with chest wall separation > 22 cm were selected for dosimetric analysis. We compared the maximum dose in the central axis (CAX) plane (2D) using 6-, 10-, and 18-MV photon beams in all patients and 3D data set for 16 patients. Correlationmore » between hot spot dose (HSD), separation, breast cup size, breast volume, and body weight was derived with beam energy. Among the 48 patients in this study, HSD > 10% in the CAX plane was noted in 98%, 46%, and 4% of the population when 2D dosimetry was performed; however, with 3D study, it was in 50%, 19%, and 6% of the patients with 6-MV, 10-MV and 18-MV beams, respectively. The chest wall separation, body weight, and breast volume were correlated with the HSD in both the 2D and 3D plans. Patient's bra size was not correlated with the hot spot. The chest wall separation was found to be the most important parameter to correlate with hot spot in tangential breast treatment. Simple guidelines are provided for dose uniformity in breast with respect to chest wall separation, body weight, bra size, and breast volume with tangential field irradiations.« less
  • Tangential radiotherapy delivered to women with large breasts can be problematic due to the excessive skin folds and the way that the breast falls into the axilla. This may necessitate excessive lung irradiation to cover the posterior part of the breast volume adequately. Conventional breast rings used to move the breast anteriorly can be very difficult to reproduce and may substantially increase the skin dose and hence skin toxicity due to the bolus effect. An in-house designed microshell device was constructed to improve setup reproducibility and minimize skin dose. Dose comparisons using a phantom were made between this device andmore » 2 other commonly used devices. The microshell successfully reduced the surface dose compared to the other breast rings tested. This device was then investigated on 8 patients under clinical conditions. Skin doses measured on the trial patients were within acceptable limits. During this small pilot study, no patients suffered excessive skin toxicity or required treatment breaks. Due to the microshell's expandable nature, ease of application, which increases patient comfort compared to other breast rings, and the lower surface dose, the microshell is the preferred breast stabilization device for this department when treating patients with large pendulous breasts. We encourage other departments to consider their current method of breast stabilization and compare them to our results.« less
  • Purpose: To report our institution's experience using prone positioning for three-dimensional conformal radiotherapy (3D-CRT) to deliver post-lumpectomy whole breast irradiation (WBI) in a cohort of women with large and/or pendulous breasts, to determine the rate of acute and late toxicities and, more specifically, cosmetic outcomes. We hypothesized that using 3D-CRT for WBI in the prone position would reduce or eliminate patient and breast size as negative prognostic indicators for toxicities associated with WBI. Methods and Materials: From 1998 to 2006, 110 cases were treated with prone WBI using 3D-CRT. The lumpectomy, breast target volumes, heart, and lung were contoured onmore » all computed tomography scans. A dose of 45-50 Gy was prescribed to the breast volume using standard fractionation schemes. The planning goals were {>=}95% of prescription to 95% of the breast volume, and 100% of boost dose to 95% of lumpectomy planning target volume. Toxicities and cosmesis were prospectively scored using the Common Terminology Criteria for Adverse Effects Version 3.0 and the Harvard Scale. The median follow-up was 40 months. Results: The median body mass index (BMI) was 33.6 kg/m{sup 2}, and median breast volume was 1396 cm{sup 3}. The worst toxicity encountered during radiation was Grade 3 dermatitis in 5% of our patient population. Moist desquamation occurred in 16% of patients, with only 2% of patients with moist desquamation outside the inframammary/axillary folds. Eleven percent of patients had Grade {>=}2 late toxicities, including Grade 3 induration/fibrosis in 2%. Excellent to good cosmesis was achieved in 89%. Higher BMI was associated with moist desquamation and breast pain, but BMI and breast volume did not impact fibrosis or excellent to good cosmesis. Conclusion: In patients with higher BMI and/or large-pendulous breasts, delivering prone WBI using 3D-CRT results in favorable toxicity profiles and high excellent to good cosmesis rates. Higher BMI was associated with moist desquamation, but prone positioning removed BMI and breast size as factors for poorer cosmetic outcomes. This series adds to the growing literature demonstrating that prone WBI may be advantageous in select patients.« less