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SU‐GG‐T‐208: 3‐D Dosimetric Comparison of IMRT with 2.5 Mm HD120 MLC Using Optical CT Based Polymer Gel and PRESAGE Dosimeters
Author(s) -
Wuu C,
Maryanski M,
Adamovics J,
Xu Y
Publication year - 2010
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 - 10.1118/1.3468597
Subject(s) - dosimeter , imaging phantom , materials science , scanner , dosimetry , nuclear medicine , optics , radiosurgery , linear particle accelerator , biomedical engineering , beam (structure) , radiation therapy , physics , medicine , radiology
Purpose: To evaluate and compare the 3‐D dose distributions for IMRT with 2.5 mm HD120 MLC using optical CT based polymer gel and PRESAGE dosimeters. Method and Materials: In this study, a polymer BANG gel dosimeter and a PRESAGE phantom, together with an optical CT scanner, were employed to implement 3‐D dose distribution measurements. Both dosimeters, with 15 cm diameter and 14 cm height, were modified to optimal and linear dose‐response characteristics. A slice thickness of 2.5 mm without spacing was used for CT simulation on both the patient and cylindrical phantoms. The Varian Eclipse treatment planning system was used to design the IMRT radiosurgery plan for a patient with a 2.5 cc small brain tumor treated with 6 MV photon beams. To correlate the optical density response with radiation dose, the same batch of gel and PRESAGE phantoms were irradiated with a 16 MeV electron beam to a known dose at the depth of dmax. The optical density at a specific depth and the PDD table of the electron beam can be used to obtain the optical density dose response of the dosimeters. Both phantoms were scanned with 1 mm pixel resolution using a commercial optical CT scanner, OCTOPUS™ (MGS Research Inc., Madison, CT). Results: Both measured dose distributions from gel and PRESAGE and calculated results are in reasonable agreement. However, the isodose lines from the measurements show more variation than those from the calculation, and this trend is more significant for the 2.5 mm MLC. These discrepancies may be partly attributed to the fact that the calculation grid for the planning system is 2.5 mm yet the resolution of gel measurements is 1 mm, as well as the Trilogy TX having a smaller leaf width. Issues and difficulties on 3‐D dosimetric comparison will be presented.