Radiation therapy of large intact breasts using a beam spoiler or photons with mixed energies Journal Article
| Authors: | Lief, E. P.; Hunt, M. A.; Hong, L. X.; Amols, H. I. |
| Article 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 × 20-cm2 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 Dmax 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. © 2007 American Association of Medical Dosimetrists. |
| Keywords: | treatment planning; cancer radiotherapy; comparative study; breast cancer; radiotherapy dosage; breast neoplasms; skin; dosimetry; measurement; radiation therapy; polystyrene; phantom; radiation beam; photons; energy; photon; diode; dose calculation; x ray; calculation; skin dose; beam spoiler; buildup |
| Journal Title: | Medical Dosimetry |
| Volume: | 32 |
| Issue: | 4 |
| ISSN: | 0958-3947 |
| Publisher: | Elsevier Science, Inc. |
| Date Published: | 2007-01-01 |
| Start Page: | 246 |
| End Page: | 253 |
| Language: | English |
| DOI: | 10.1016/j.meddos.2007.02.002 |
| PUBMED: | 17980824 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | The publisher's record lists the publication date as Winter -- "Cited By (since 1996): 2" -- "Export Date: 17 November 2011" -- "CODEN: MEDOE" -- "Source: Scopus" |
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