Surface and build‐up region dosimetry for obliquely incident intensity modulated radiotherapy 6 MV x rays
- 18 November 2003
- journal article
- research article
- Published by Wiley in Medical Physics
- Vol. 30 (12), 3091-3096
- https://doi.org/10.1118/1.1625116
Abstract
This study investigates the surface dose and build-up region dosimetry for oblique IMRT beams. The dependence of surface and build-up region doses of 0 degrees (perpendicular incidence) and 75 degrees (oblique incidence) IMRT fields on field size was measured and compared with open field dosimetry. Measurements were performed using a parallel-plate chamber and KODAK EDR2 films in a polystyrene phantom for a 6 cm x 6 cm and a 12 cm x 12 cm, 6 MV photon beam at depths of 0 mm (surface) through dmax. Data were normalized to the dmax value of each field. Four intensity modulated delivery patterns were created and delivered using step-and-shoot IMRT: (1) six static 1 cm x 6 cm strips (IMRTstrip), (2) 12 static 1 cm x 12 cm strips (IMRTstrip), (3) intensity modulated beam patterns created by using the inverse planning optimization software (IMRTopt) for 6 cm x 6 cm, and (4) IMRTopt for 12 cm x 12 cm field sizes. The percent depth doses (PDDs) of 0 degrees, 6 cm x 6 cm IMRTstrip beam at the surface and 5 mm were lower by 8.8% and 1.6%, respectively, compared to the open field. The PDDs of 75 degrees, 6 cm x 6 cm IMRTstrip beam at the surface and 5 mm were lower by 6.7% and 2.4%, respectively, compared to the open field. This study showed that IMRT itself is not contributing to greater skin doses.Keywords
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