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Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy

PURPOSE: Passive Radiotherapy Intensity Modulators for Electrons (PRIME) devices are comprised of cylindrical tungsten island blocks imbedded in a machinable foam slab within the patient's cutout. Intensity‐modulated bolus electron conformal therapy (IM‐BECT) uses PRIME devices to reduce dose h...

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Autores principales: Scotto, Joseph G., Pitcher, Garrett M., Carver, Robert L., Erhart, Kevin J., McGuffey, Andrew S., Hogstrom, Kenneth R.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9924125/
https://www.ncbi.nlm.nih.gov/pubmed/36610042
http://dx.doi.org/10.1002/acm2.13889
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author Scotto, Joseph G.
Pitcher, Garrett M.
Carver, Robert L.
Erhart, Kevin J.
McGuffey, Andrew S.
Hogstrom, Kenneth R.
author_facet Scotto, Joseph G.
Pitcher, Garrett M.
Carver, Robert L.
Erhart, Kevin J.
McGuffey, Andrew S.
Hogstrom, Kenneth R.
author_sort Scotto, Joseph G.
collection PubMed
description PURPOSE: Passive Radiotherapy Intensity Modulators for Electrons (PRIME) devices are comprised of cylindrical tungsten island blocks imbedded in a machinable foam slab within the patient's cutout. Intensity‐modulated bolus electron conformal therapy (IM‐BECT) uses PRIME devices to reduce dose heterogeneity caused by the irregular bolus surface. Heretofore, IM‐BECT dose calculations used the pencil beam redefinition algorithm (PBRA) assuming perfect collimation. This study investigates modeling electron scatter into and out the sides of island blocks. METHODS: Dose distributions were measured in a water phantom at 7, 13, and 20 MeV for devices having nominal intensity reduction factors of 1.000 (foam only), 0.937, 0.812, and 0.688, corresponding to nominal island block diameters (d(nom) ) of 0.158, 0.273, and 0.352 cm, respectively. Pencil beam theory derived an effective diameter (d(IS) ) to account for in‐scattered electrons as a function of d(nom) and beam energy (E(p,0) ). However, for out‐scattered electrons, an effective diameter (d(mod) ) was estimated by best fitting measured data. RESULTS: In the modulated region (under island blocks, depth < R(90)), modified PBRA‐calculated dose distributions showed 2%/2 mm passing rates for d(nom)  = 0.158, 0.273, and 0.352 cm of (100%, 100%, 100%) at 7 MeV, (100%, 100%, 93.5%) at 13 MeV, and (99.8%, 85.4%, and 71.5%) at 20 MeV. The largest dose differences (≤ 6%) occurred at the highest energy (20 MeV), largest d(nom) , shallowest depths (≤ 2 cm), and on central axis. CONCLUSIONS: An equation for modeling island block scatter, d(mod) (d(nom) , E(p,0) ), has been developed for use in the PBRA, insignificantly impacting calculation time. Although inaccuracy sometimes exceeded our 2%/2 mm criteria, it could be clinically acceptable, as superficial dose differences often fall inside the bolus. Also, patient PRIME devices are expected to have fewer large diameter island blocks than did test devices. Inaccuracies are attributed to out‐scattered electrons having energy spectra different than the primary beams.
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spelling pubmed-99241252023-02-14 Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy Scotto, Joseph G. Pitcher, Garrett M. Carver, Robert L. Erhart, Kevin J. McGuffey, Andrew S. Hogstrom, Kenneth R. J Appl Clin Med Phys Review Articles PURPOSE: Passive Radiotherapy Intensity Modulators for Electrons (PRIME) devices are comprised of cylindrical tungsten island blocks imbedded in a machinable foam slab within the patient's cutout. Intensity‐modulated bolus electron conformal therapy (IM‐BECT) uses PRIME devices to reduce dose heterogeneity caused by the irregular bolus surface. Heretofore, IM‐BECT dose calculations used the pencil beam redefinition algorithm (PBRA) assuming perfect collimation. This study investigates modeling electron scatter into and out the sides of island blocks. METHODS: Dose distributions were measured in a water phantom at 7, 13, and 20 MeV for devices having nominal intensity reduction factors of 1.000 (foam only), 0.937, 0.812, and 0.688, corresponding to nominal island block diameters (d(nom) ) of 0.158, 0.273, and 0.352 cm, respectively. Pencil beam theory derived an effective diameter (d(IS) ) to account for in‐scattered electrons as a function of d(nom) and beam energy (E(p,0) ). However, for out‐scattered electrons, an effective diameter (d(mod) ) was estimated by best fitting measured data. RESULTS: In the modulated region (under island blocks, depth < R(90)), modified PBRA‐calculated dose distributions showed 2%/2 mm passing rates for d(nom)  = 0.158, 0.273, and 0.352 cm of (100%, 100%, 100%) at 7 MeV, (100%, 100%, 93.5%) at 13 MeV, and (99.8%, 85.4%, and 71.5%) at 20 MeV. The largest dose differences (≤ 6%) occurred at the highest energy (20 MeV), largest d(nom) , shallowest depths (≤ 2 cm), and on central axis. CONCLUSIONS: An equation for modeling island block scatter, d(mod) (d(nom) , E(p,0) ), has been developed for use in the PBRA, insignificantly impacting calculation time. Although inaccuracy sometimes exceeded our 2%/2 mm criteria, it could be clinically acceptable, as superficial dose differences often fall inside the bolus. Also, patient PRIME devices are expected to have fewer large diameter island blocks than did test devices. Inaccuracies are attributed to out‐scattered electrons having energy spectra different than the primary beams. John Wiley and Sons Inc. 2023-01-07 /pmc/articles/PMC9924125/ /pubmed/36610042 http://dx.doi.org/10.1002/acm2.13889 Text en © 2023 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine. https://creativecommons.org/licenses/by/4.0/This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ (https://creativecommons.org/licenses/by/4.0/) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Review Articles
Scotto, Joseph G.
Pitcher, Garrett M.
Carver, Robert L.
Erhart, Kevin J.
McGuffey, Andrew S.
Hogstrom, Kenneth R.
Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy
title Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy
title_full Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy
title_fullStr Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy
title_full_unstemmed Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy
title_short Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy
title_sort modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy
topic Review Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9924125/
https://www.ncbi.nlm.nih.gov/pubmed/36610042
http://dx.doi.org/10.1002/acm2.13889
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