Fontenla DP, Napoli JJ, Hunt M, Fass D, McCormick B, Kutcher GJ. Effects of beam modifiers and immobilization devices on the dose in the build-up region.
Int J Radiat Oncol Biol Phys 1994;
30:211-9. [PMID:
8083116 DOI:
10.1016/0360-3016(94)90537-1]
[Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
PURPOSE
To analyze the effect that immobilization devices used in conjunction with beam modifiers may have on the dose to the skin and build-up region.
METHODS AND MATERIALS
Central axis depth dose measurements were made in a polystyrene phantom in the build-up regions using the 6 and 15 MV photon beams, at two different source-to-phantom distances, and various field sizes. The effects of acrylic blocking trays, lead wedges, and cerrobend blocks were assessed in conjunction with the enhancement of dose in the build-up region due to immobilizing devices using plaster and thermoplastic casting materials of different thicknesses.
RESULTS
For the 6 MV photons, solid (3 mm) thermoplastic casting material was found to have the greatest effect on surface dose: for a 12 x 12 cm field we measured 79% of maximum dose when treating through the material versus 22% of maximum dose when no beam modifiers or immobilization devices are used. Measurements were also made to evaluate the effect of the immobilization of patients receiving three-dimensional conformal treatments using a 15 MV photon beam.
CONCLUSIONS
The relevance of these results to treatments in the pelvis, breast, and head and neck regions is discussed. For 6 MV beams, special consideration should be given if the need arises to treat through the immobilization device, as unacceptable skin reactions may result.
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