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SU‐FF‐T‐367: Radiochromic Film and Ion Chamber Dosimetry for Monochromatic X‐Rays in PMMA
Author(s) -
Oves S,
Dugas J,
Hogstrom K
Publication year - 2007
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 - 10.1118/1.2761092
Subject(s) - dosimetry , ionization chamber , monochromatic color , dosimeter , imaging phantom , optics , materials science , faraday cup , calibration , absorbed dose , x ray , beam (structure) , dose profile , nuclear medicine , ion beam , physics , ion , radiation , ionization , medicine , quantum mechanics
Purpose: K‐edge capture radiotherapy using monochromatic, keV x‐ray beams necessitates accompanying dosimetry methods. This work compares radiochromic film and ion chamber dosimetry methods potentially suitable for use with monochromatic x‐ray beams. Method and Materials: X‐rays were produced at the LSU CAMD synchrotron by passing a 1.3‐GeV electron beam (≈200‐mA) through a 7‐T superconducting wiggler. The resulting polychromatic beam was passed through a double multilayer monochromator to generate an approximately 0.1×2.8‐cm 2 , 35‐keV x‐ray beam. A 2.5×2.8‐cm 2 broad beam was produced via oscillation of phantom and dosimeters by a triangular waveform. Central‐axis depth dose was measured in a 10×10×12.5‐cm 3 PMMA slab phantom using 5.12×5.12‐cm 2 GAFChromic® EBT films and an air‐equivalent, cylindrical ion chamber (0.23‐cm 3 ). Films were digitized using the red channel of a flatbed scanner, and pixel values were converted to dose using both 6‐MV x‐ray and125 I brachytherapy seed calibration curves.125 I doses were calculated using AAPM TG‐43 formalism. Ion chamber charge readings were converted to dose using the AAPM TG‐61 protocol for kilovoltage x‐ray beam dosimetry. Results: Measurements in a PMMA phantom yielded film depth‐dose curves from film that were 2.5–4.4% higher than those from the ion chamber for depths of 0 to 9 cm when using the125 I seed calibration. Using the 6‐MV x‐ray dose calibration for film resulted in doses approximately 35% lower due to a significantly different film calibration curve compared to that using125 I seeds. Conclusion: These methods should be suitable for future dose measurements required for cell and small animal irradiations. The discrepancy between 6‐MV x‐rays and125 I seeds is contrary to previously reported results and currently under investigation.