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Title: Quality assurance for radiotherapy in prostate cancer: Point dose measurements in intensity modulated fields with large dose gradients

Abstract

Purpose: We aimed to evaluate an optimization algorithm designed to find the most favorable points to position an ionization chamber (IC) for quality assurance dose measurements of patients treated for prostate cancer with intensity-modulated radiotherapy (IMRT) and fields up to 10 cm x 10 cm. Methods and Materials: Three cylindrical ICs (PTW, Freiburg, Germany) were used with volumes of 0.6 cc, 0.125 cc, and 0.015 cc. Dose measurements were made in a plastic phantom (PMMA) at 287 optimized points. An algorithm was designed to search for points with the lowest dose gradient. Measurements were made also at 39 nonoptimized points. Results were normalized to a reference homogeneous field introducing a dose ratio factor, which allowed us to compare measured vs. calculated values as percentile dose ratio factor deviations {delta}F (%). A tolerance range of {delta}F (%) of {+-}3% was considered. Results: Half of the {delta}F (%) values obtained at nonoptimized points were outside the acceptable range. Values at optimized points were widely spread for the largest IC (i.e., 60% of the results outside the tolerance range), whereas for the two small-volume ICs, only 14.6% of the results were outside the tolerance interval. No differences were observed when comparing the twomore » small ICs. Conclusions: The presented optimization algorithm is a useful tool to determine the best IC in-field position for optimal dose measurement conditions. A good agreement between calculated and measured doses can be obtained by positioning small volume chambers at carefully selected points in the field. Large chambers may be unreliable even in optimized points for IMRT fields {<=}10 cm x 10 cm.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Servei de Radio-oncologia, Instituto Oncologico Teknon, Barcelona (Spain)
Publication Date:
OSTI Identifier:
20850206
Resource Type:
Journal Article
Journal Name:
International Journal of Radiation Oncology, Biology and Physics
Additional Journal Information:
Journal Volume: 66; Journal Issue: 4; Other Information: DOI: 10.1016/j.ijrobp.2006.01.055; PII: S0360-3016(06)02661-7; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0360-3016
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ALGORITHMS; BEAMS; CARCINOMAS; COLLIMATORS; IONIZATION CHAMBERS; OPTIMIZATION; PATIENTS; PHANTOMS; PLASTICS; PMMA; PROSTATE; QUALITY ASSURANCE; RADIATION DOSES; RADIOTHERAPY; SURGERY; TOLERANCE

Citation Formats

Escude, Lluis, Linero, Dolors, Molla, Meritxell, Miralbell, Raymond, and Service de Radio-oncologie, Hopitaux Universitaires, Geneva. Quality assurance for radiotherapy in prostate cancer: Point dose measurements in intensity modulated fields with large dose gradients. United States: N. p., 2006. Web. doi:10.1016/j.ijrobp.2006.01.055.
Escude, Lluis, Linero, Dolors, Molla, Meritxell, Miralbell, Raymond, & Service de Radio-oncologie, Hopitaux Universitaires, Geneva. Quality assurance for radiotherapy in prostate cancer: Point dose measurements in intensity modulated fields with large dose gradients. United States. https://doi.org/10.1016/j.ijrobp.2006.01.055
Escude, Lluis, Linero, Dolors, Molla, Meritxell, Miralbell, Raymond, and Service de Radio-oncologie, Hopitaux Universitaires, Geneva. 2006. "Quality assurance for radiotherapy in prostate cancer: Point dose measurements in intensity modulated fields with large dose gradients". United States. https://doi.org/10.1016/j.ijrobp.2006.01.055.
@article{osti_20850206,
title = {Quality assurance for radiotherapy in prostate cancer: Point dose measurements in intensity modulated fields with large dose gradients},
author = {Escude, Lluis and Linero, Dolors and Molla, Meritxell and Miralbell, Raymond and Service de Radio-oncologie, Hopitaux Universitaires, Geneva},
abstractNote = {Purpose: We aimed to evaluate an optimization algorithm designed to find the most favorable points to position an ionization chamber (IC) for quality assurance dose measurements of patients treated for prostate cancer with intensity-modulated radiotherapy (IMRT) and fields up to 10 cm x 10 cm. Methods and Materials: Three cylindrical ICs (PTW, Freiburg, Germany) were used with volumes of 0.6 cc, 0.125 cc, and 0.015 cc. Dose measurements were made in a plastic phantom (PMMA) at 287 optimized points. An algorithm was designed to search for points with the lowest dose gradient. Measurements were made also at 39 nonoptimized points. Results were normalized to a reference homogeneous field introducing a dose ratio factor, which allowed us to compare measured vs. calculated values as percentile dose ratio factor deviations {delta}F (%). A tolerance range of {delta}F (%) of {+-}3% was considered. Results: Half of the {delta}F (%) values obtained at nonoptimized points were outside the acceptable range. Values at optimized points were widely spread for the largest IC (i.e., 60% of the results outside the tolerance range), whereas for the two small-volume ICs, only 14.6% of the results were outside the tolerance interval. No differences were observed when comparing the two small ICs. Conclusions: The presented optimization algorithm is a useful tool to determine the best IC in-field position for optimal dose measurement conditions. A good agreement between calculated and measured doses can be obtained by positioning small volume chambers at carefully selected points in the field. Large chambers may be unreliable even in optimized points for IMRT fields {<=}10 cm x 10 cm.},
doi = {10.1016/j.ijrobp.2006.01.055},
url = {https://www.osti.gov/biblio/20850206}, journal = {International Journal of Radiation Oncology, Biology and Physics},
issn = {0360-3016},
number = 4,
volume = 66,
place = {United States},
year = {Wed Nov 15 00:00:00 EST 2006},
month = {Wed Nov 15 00:00:00 EST 2006}
}