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Title: SU-E-T-35: A General Fill Factor Definition Serving to Characterise the MLC Misalignment Detection Capabilities of Two-Dimensional Detector Arrays

Abstract

Purpose: To present a general definition of the fill factor realistically characterizing the “field coverage”, i.e. the MLC misalignment detection capabilities of a detector array. Methods: According to Gago-Arias et al.{sup 1} the fill factor of a 2D array is defined as the ratio of the area enclosed by the FWHM of the fluence response function KM(x) of a single detector and its cell area defined by the detector spacing. More generally - accounting also for the possible overlap between FWHM’s of neighboured detectors - the fill factor is here defined as that fraction of the sum of the detector cell areas in which a defined MLC misalignment is detectable when the induced percentage signal changes exceed a detection threshold d. Ideally the generalized fill factor may reach 100 %. With user code EGS-chamber and a 2 MeV photon slit beam 0.25 mm wide, both types of the fill factor were calculated for an array with total cell area 100 cm{sup 2} for chamber widths 1–9 mm, using =1mm, d=5%. Results: For single chamber width 5 mm, fill factors were 0.49 (FWHM) and 0.61 (generalized). For chamber width 2 mm the FWHM fill factor was 0.13 whereas the generalized fillmore » factor was 0.32. For chamber widths above 7 mm, the FWHM fill factor exceeds unity, and the general fill factor is exactly 1.00. Conclusions: An updated fill factor definition is introduced which, as a generalization of the FWHM-based definition, more closely estimates the performance of small array chambers and gives a realistic value in the case of overlapping sensitive areas of neighboured chambers. References:{sup 1}A. Gago-Arias, L. Brualla-Gonzalez, D.M. Gonzalez-Castano, F. Gomez, M.S. Garcia, V.L. Vega, J.M. Sueiro, J. Pardo-Montero, “Evaluation of chamber response function influence on IMRT verification using 2D commercial detector arrays,” Phys. Med. Biol. 57, 2005–2020 (2012)« less

Authors:
; ;  [1];  [2];  [3]
  1. Clinic for Radiation Therapy, Pius-Hospital, Oldenburg, DE (United States)
  2. (United States)
  3. Prof. em., Medical Physics and Biophysics, Georg August University, Goettingen, DE (Germany)
Publication Date:
OSTI Identifier:
22545168
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; COLLIMATORS; DETECTION; EVALUATION; FILL FACTORS; PERFORMANCE; RADIOTHERAPY; RESPONSE FUNCTIONS; VERIFICATION

Citation Formats

Stelljes, T.S., Looe, H.K., Poppe, B., WG Medical Radiation Physics, Carl von Ossietzky University, Oldenburg, DE, and Harder, D.. SU-E-T-35: A General Fill Factor Definition Serving to Characterise the MLC Misalignment Detection Capabilities of Two-Dimensional Detector Arrays. United States: N. p., 2015. Web. doi:10.1118/1.4924396.
Stelljes, T.S., Looe, H.K., Poppe, B., WG Medical Radiation Physics, Carl von Ossietzky University, Oldenburg, DE, & Harder, D.. SU-E-T-35: A General Fill Factor Definition Serving to Characterise the MLC Misalignment Detection Capabilities of Two-Dimensional Detector Arrays. United States. doi:10.1118/1.4924396.
Stelljes, T.S., Looe, H.K., Poppe, B., WG Medical Radiation Physics, Carl von Ossietzky University, Oldenburg, DE, and Harder, D.. Mon . "SU-E-T-35: A General Fill Factor Definition Serving to Characterise the MLC Misalignment Detection Capabilities of Two-Dimensional Detector Arrays". United States. doi:10.1118/1.4924396.
@article{osti_22545168,
title = {SU-E-T-35: A General Fill Factor Definition Serving to Characterise the MLC Misalignment Detection Capabilities of Two-Dimensional Detector Arrays},
author = {Stelljes, T.S. and Looe, H.K. and Poppe, B. and WG Medical Radiation Physics, Carl von Ossietzky University, Oldenburg, DE and Harder, D.},
abstractNote = {Purpose: To present a general definition of the fill factor realistically characterizing the “field coverage”, i.e. the MLC misalignment detection capabilities of a detector array. Methods: According to Gago-Arias et al.{sup 1} the fill factor of a 2D array is defined as the ratio of the area enclosed by the FWHM of the fluence response function KM(x) of a single detector and its cell area defined by the detector spacing. More generally - accounting also for the possible overlap between FWHM’s of neighboured detectors - the fill factor is here defined as that fraction of the sum of the detector cell areas in which a defined MLC misalignment is detectable when the induced percentage signal changes exceed a detection threshold d. Ideally the generalized fill factor may reach 100 %. With user code EGS-chamber and a 2 MeV photon slit beam 0.25 mm wide, both types of the fill factor were calculated for an array with total cell area 100 cm{sup 2} for chamber widths 1–9 mm, using =1mm, d=5%. Results: For single chamber width 5 mm, fill factors were 0.49 (FWHM) and 0.61 (generalized). For chamber width 2 mm the FWHM fill factor was 0.13 whereas the generalized fill factor was 0.32. For chamber widths above 7 mm, the FWHM fill factor exceeds unity, and the general fill factor is exactly 1.00. Conclusions: An updated fill factor definition is introduced which, as a generalization of the FWHM-based definition, more closely estimates the performance of small array chambers and gives a realistic value in the case of overlapping sensitive areas of neighboured chambers. References:{sup 1}A. Gago-Arias, L. Brualla-Gonzalez, D.M. Gonzalez-Castano, F. Gomez, M.S. Garcia, V.L. Vega, J.M. Sueiro, J. Pardo-Montero, “Evaluation of chamber response function influence on IMRT verification using 2D commercial detector arrays,” Phys. Med. Biol. 57, 2005–2020 (2012)},
doi = {10.1118/1.4924396},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}