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Dosimetric characteristics of 6 and 10 MV unflattened photon beams

Kragl, Gabriele; Wetterstedt, Sacha Af; Knaeusl, Barbara; Dalaryd, Mårten LU ; McCavana, Patrick; Knöös, Tommy LU ; McClean, Brendan and Georg, Dietmar (2009) In Radiotherapy and Oncology 93(1). p.141-146
Abstract
Purpose: To determine dosimetric properties of unflattened megavoltage photon beams. Materials and methods: Dosimetric data including depth dose, profiles, output factors and phantom scatter factors from three different beam qualities provided by Elekta Precise linacs, operated with and without flattening filter were examined. Additional measurements of leaf transmission, leakage radiation and surface dose were performed. In flattening filter free (FFF) mode a 6-mm thick copper filter was placed into the beam to stabilize it. Results: Depths of dose maxima for flattened and unflattened beams did not deviate by more than 2 mm and penumbral widths agreed within 1 mm. In FFF mode the collimator exchange effect was found to be on average 0.3%... (More)
Purpose: To determine dosimetric properties of unflattened megavoltage photon beams. Materials and methods: Dosimetric data including depth dose, profiles, output factors and phantom scatter factors from three different beam qualities provided by Elekta Precise linacs, operated with and without flattening filter were examined. Additional measurements of leaf transmission, leakage radiation and surface dose were performed. In flattening filter free (FFF) mode a 6-mm thick copper filter was placed into the beam to stabilize it. Results: Depths of dose maxima for flattened and unflattened beams did not deviate by more than 2 mm and penumbral widths agreed within 1 mm. In FFF mode the collimator exchange effect was found to be on average 0.3% for rectangular fields. Between maximum and minimum field size head scatter factors of unflattened beams showed on average 40% and 56% less variation for 6 and 10 MV beams than conventional beams. Phantom scatter factors for FFF beams differed up to 4% from the published reference data. For field sizes smaller than 15 cm, surface doses relative to the dose at d(max) increased for unflattened beams with maximum differences of 7% at 6 MV and 25% at 10 MV for a 5 x 5 cm(2) field. For a 30 x 30 cm(2) field, relative surface dose decreased by about 10% for FFF beams. Leaf transmission on the central axis was 0.3% and 0.4% lower for unflattened 6 and 10 MV beams, respectively. Leakage radiation was reduced by 52% for 6 MV and by 65% for 10 MV unflattened beams. Conclusions: The results of the study were independently confirmed at two radiotherapy centres. Phantom scatter reference data need to be reconsidered for medical accelerators operated without a flattening filter. (C) 2009 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 93 (2009) 141-146 (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Basic beam properties, Flattening filter free (FFF), IMRT
in
Radiotherapy and Oncology
volume
93
issue
1
pages
141 - 146
publisher
Elsevier
external identifiers
  • wos:000271046500023
  • scopus:70349315242
ISSN
1879-0887
DOI
10.1016/j.radonc.2009.06.008
language
English
LU publication?
yes
id
ef1069cb-2341-4cac-b719-907519e8ca79 (old id 1505301)
date added to LUP
2009-11-24 13:36:59
date last changed
2017-12-10 03:52:33
@article{ef1069cb-2341-4cac-b719-907519e8ca79,
  abstract     = {Purpose: To determine dosimetric properties of unflattened megavoltage photon beams. Materials and methods: Dosimetric data including depth dose, profiles, output factors and phantom scatter factors from three different beam qualities provided by Elekta Precise linacs, operated with and without flattening filter were examined. Additional measurements of leaf transmission, leakage radiation and surface dose were performed. In flattening filter free (FFF) mode a 6-mm thick copper filter was placed into the beam to stabilize it. Results: Depths of dose maxima for flattened and unflattened beams did not deviate by more than 2 mm and penumbral widths agreed within 1 mm. In FFF mode the collimator exchange effect was found to be on average 0.3% for rectangular fields. Between maximum and minimum field size head scatter factors of unflattened beams showed on average 40% and 56% less variation for 6 and 10 MV beams than conventional beams. Phantom scatter factors for FFF beams differed up to 4% from the published reference data. For field sizes smaller than 15 cm, surface doses relative to the dose at d(max) increased for unflattened beams with maximum differences of 7% at 6 MV and 25% at 10 MV for a 5 x 5 cm(2) field. For a 30 x 30 cm(2) field, relative surface dose decreased by about 10% for FFF beams. Leaf transmission on the central axis was 0.3% and 0.4% lower for unflattened 6 and 10 MV beams, respectively. Leakage radiation was reduced by 52% for 6 MV and by 65% for 10 MV unflattened beams. Conclusions: The results of the study were independently confirmed at two radiotherapy centres. Phantom scatter reference data need to be reconsidered for medical accelerators operated without a flattening filter. (C) 2009 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 93 (2009) 141-146},
  author       = {Kragl, Gabriele and Wetterstedt, Sacha Af and Knaeusl, Barbara and Dalaryd, Mårten and McCavana, Patrick and Knöös, Tommy and McClean, Brendan and Georg, Dietmar},
  issn         = {1879-0887},
  keyword      = {Basic beam properties,Flattening filter free (FFF),IMRT},
  language     = {eng},
  number       = {1},
  pages        = {141--146},
  publisher    = {Elsevier},
  series       = {Radiotherapy and Oncology},
  title        = {Dosimetric characteristics of 6 and 10 MV unflattened photon beams},
  url          = {http://dx.doi.org/10.1016/j.radonc.2009.06.008},
  volume       = {93},
  year         = {2009},
}