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Title: An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields

Abstract

Purpose: An experimental extrapolation technique is presented, which can be used to determine the relative output factors for very small x-ray fields using the Gafchromic EBT3 film. Methods: Relative output factors were measured for the Brainlab SRS cones ranging in diameters from 4 to 30 mm{sup 2} on a Novalis Trilogy linear accelerator with 6 MV SRS x-rays. The relative output factor was determined from an experimental reducing circular region of interest (ROI) extrapolation technique developed to remove the effects of volume averaging. This was achieved by scanning the EBT3 film measurements with a high scanning resolution of 1200 dpi. From the high resolution scans, the size of the circular regions of interest was varied to produce a plot of relative output factors versus area of analysis. The plot was then extrapolated to zero to determine the relative output factor corresponding to zero volume. Results: Results have shown that for a 4 mm field size, the extrapolated relative output factor was measured as a value of 0.651 ± 0.018 as compared to 0.639 ± 0.019 and 0.633 ± 0.021 for 0.5 and 1.0 mm diameter of analysis values, respectively. This showed a change in the relative output factors of 1.8% and 2.8% at these comparative regionsmore » of interest sizes. In comparison, the 25 mm cone had negligible differences in the measured output factor between zero extrapolation, 0.5 and 1.0 mm diameter ROIs, respectively. Conclusions: This work shows that for very small fields such as 4.0 mm cone sizes, a measureable difference can be seen in the relative output factor based on the circular ROI and the size of the area of analysis using radiochromic film dosimetry. The authors recommend to scan the Gafchromic EBT3 film at a resolution of 1200 dpi for cone sizes less than 7.5 mm and to utilize an extrapolation technique for the output factor measurements of very small field dosimetry.« less

Authors:
;  [1];  [2];  [3]
  1. Department of Radiation Oncology, Chris O’Brien Lifehouse, 119-143 Missenden Road, Camperdown, NSW 2050, Australia and Institute of Medical Physics, University of Sydney, NSW 2006 (Australia)
  2. School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, Level 4 O Block, Garden’s Point, QLD 4001, Australia and Cancer Care Services, Royal Brisbane and Women’s Hospital, Butterfield Street, Herston, QLD 4029 (Australia)
  3. School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, Level 4 O Block, Garden’s Point, QLD 4001 (Australia)
Publication Date:
OSTI Identifier:
22689441
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 43; Journal Issue: 8; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; 60 APPLIED LIFE SCIENCES; EXTRAPOLATION; FILM DOSIMETRY; LINEAR ACCELERATORS; RESOLUTION; X RADIATION

Citation Formats

Morales, Johnny E., E-mail: johnny.morales@lh.org.au, Butson, Martin, Hill, Robin, Crowe, Scott B., and Trapp, J. V. An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields. United States: N. p., 2016. Web. doi:10.1118/1.4958679.
Morales, Johnny E., E-mail: johnny.morales@lh.org.au, Butson, Martin, Hill, Robin, Crowe, Scott B., & Trapp, J. V. An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields. United States. https://doi.org/10.1118/1.4958679
Morales, Johnny E., E-mail: johnny.morales@lh.org.au, Butson, Martin, Hill, Robin, Crowe, Scott B., and Trapp, J. V. 2016. "An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields". United States. https://doi.org/10.1118/1.4958679.
@article{osti_22689441,
title = {An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields},
author = {Morales, Johnny E., E-mail: johnny.morales@lh.org.au and Butson, Martin and Hill, Robin and Crowe, Scott B. and Trapp, J. V.},
abstractNote = {Purpose: An experimental extrapolation technique is presented, which can be used to determine the relative output factors for very small x-ray fields using the Gafchromic EBT3 film. Methods: Relative output factors were measured for the Brainlab SRS cones ranging in diameters from 4 to 30 mm{sup 2} on a Novalis Trilogy linear accelerator with 6 MV SRS x-rays. The relative output factor was determined from an experimental reducing circular region of interest (ROI) extrapolation technique developed to remove the effects of volume averaging. This was achieved by scanning the EBT3 film measurements with a high scanning resolution of 1200 dpi. From the high resolution scans, the size of the circular regions of interest was varied to produce a plot of relative output factors versus area of analysis. The plot was then extrapolated to zero to determine the relative output factor corresponding to zero volume. Results: Results have shown that for a 4 mm field size, the extrapolated relative output factor was measured as a value of 0.651 ± 0.018 as compared to 0.639 ± 0.019 and 0.633 ± 0.021 for 0.5 and 1.0 mm diameter of analysis values, respectively. This showed a change in the relative output factors of 1.8% and 2.8% at these comparative regions of interest sizes. In comparison, the 25 mm cone had negligible differences in the measured output factor between zero extrapolation, 0.5 and 1.0 mm diameter ROIs, respectively. Conclusions: This work shows that for very small fields such as 4.0 mm cone sizes, a measureable difference can be seen in the relative output factor based on the circular ROI and the size of the area of analysis using radiochromic film dosimetry. The authors recommend to scan the Gafchromic EBT3 film at a resolution of 1200 dpi for cone sizes less than 7.5 mm and to utilize an extrapolation technique for the output factor measurements of very small field dosimetry.},
doi = {10.1118/1.4958679},
url = {https://www.osti.gov/biblio/22689441}, journal = {Medical Physics},
issn = {0094-2405},
number = 8,
volume = 43,
place = {United States},
year = {Mon Aug 15 00:00:00 EDT 2016},
month = {Mon Aug 15 00:00:00 EDT 2016}
}