Effects of beam modifiers and immobilization devices on the dose in the build-up region. Academic Article uri icon

Overview

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.

publication date

  • August 30, 1994

Research

keywords

  • Immobilization
  • Radiotherapy Planning, Computer-Assisted
  • Skin

Identity

Scopus Document Identifier

  • 0027963155

PubMed ID

  • 8083116

Additional Document Info

volume

  • 30

issue

  • 1