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Surface and build‐up region dosimetry for obliquely incident intensity modulated radiotherapy 6 MV x rays
Author(s) -
Dogan Nesrin,
Glasgow Glenn P.
Publication year - 2003
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1625116
Subject(s) - dosimetry , optics , medical physics , radiation therapy , nuclear medicine , radiation , intensity (physics) , physics , materials science , medical imaging , medicine , radiology
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 ° (perpendicular incidence) and 75 ° (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 × 6 cm and a 12 cm × 12 cm , 6 MV photon beam at depths of 0 mm (surface) through d max . Data were normalized to the d maxvalue of each field. Four intensity modulated delivery patterns were created and delivered using step‐and‐shoot IMRT: (1) six static 1 cm × 6 cm strips ( IMRT strip) , (2) 12 static 1 cm × 12 cm strips ( IMRT strip) , (3) intensity modulated beam patterns created by using the inverse planning optimization software ( IMRT opt ) for 6 cm × 6 cm , and (4) IMRT optfor 12 cm × 12 cm field sizes. The percent depth doses (PDDs) of 0 ° ,6 cm × 6 cmIMRT stripbeam at the surface and 5 mm were lower by 8.8% and 1.6%, respectively, compared to the open field. The PDDs of 75 ° ,6 cm × 6 cmIMRT stripbeam 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.