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Title: SU-E-T-550: Range Effects in Proton Therapy Caused by Systematic Errors in the Stoichiometric Calibration

Abstract

Purpose: The procedure for proton treatment planning involves the conversion of the patient's X-ray CT from Hounsfield units into relative stopping powers (RSP), using a stoichiometric calibration curve (Schneider 1996). In clinical practice a 3.5% margin is added to account for the range uncertainty introduced by this process and other errors. RSPs for real tissues are calculated using composition data and the Bethe-Bloch formula (ICRU 1993). The purpose of this work is to investigate the impact that systematic errors in the stoichiometric calibration have on the proton range. Methods: Seven tissue inserts of the Gammex 467 phantom were imaged using our CT scanner. Their known chemical compositions (Watanabe 1999) were then used to calculate the theoretical RSPs, using the same formula as would be used for human tissues in the stoichiometric procedure. The actual RSPs of these inserts were measured using a Bragg peak shift measurement in the proton beam at our institution. Results: The theoretical calculation of the RSP was lower than the measured RSP values, by a mean/max error of - 1.5/-3.6%. For all seven inserts the theoretical approach underestimated the RSP, with errors variable across the range of Hounsfield units. Systematic errors for lung (average of twomore » inserts), adipose and cortical bone were - 3.0/-2.1/-0.5%, respectively. Conclusion: There is a systematic underestimation caused by the theoretical calculation of RSP; a crucial step in the stoichiometric calibration procedure. As such, we propose that proton calibration curves should be based on measured RSPs. Investigations will be made to see if the same systematic errors exist for biological tissues. The impact of these differences on the range of proton beams, for phantoms and patient scenarios, will be investigated. This project was funded equally by the Engineering and Physical Sciences Research Council (UK) and Ion Beam Applications (Louvain-La-Neuve, Belgium)« less

Authors:
 [1];  [2];  [2];  [2]
  1. University College London, London (United Kingdom)
  2. Massachusetts General Hospital, Boston, MA (United States)
Publication Date:
OSTI Identifier:
22369671
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 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:
60 APPLIED LIFE SCIENCES; ANIMAL TISSUES; BRAGG CURVE; CALIBRATION; ERRORS; LUNGS; PHANTOMS; PROTON BEAMS; RADIOTHERAPY; SKELETON; STOICHIOMETRY

Citation Formats

Doolan, P, Massachusetts General Hospital, Boston, MA, Dias, M, Dipartamento di Elettronica, Informazione e Bioingegneria - DEIB, Politecnico di Milano, Collins Fekete, C, Departement de physique, de genie physique et d'optique et Centre de recherche sur le cancer, Universite Laval, Quebec, and Seco, J. SU-E-T-550: Range Effects in Proton Therapy Caused by Systematic Errors in the Stoichiometric Calibration. United States: N. p., 2014. Web. doi:10.1118/1.4888885.
Doolan, P, Massachusetts General Hospital, Boston, MA, Dias, M, Dipartamento di Elettronica, Informazione e Bioingegneria - DEIB, Politecnico di Milano, Collins Fekete, C, Departement de physique, de genie physique et d'optique et Centre de recherche sur le cancer, Universite Laval, Quebec, & Seco, J. SU-E-T-550: Range Effects in Proton Therapy Caused by Systematic Errors in the Stoichiometric Calibration. United States. https://doi.org/10.1118/1.4888885
Doolan, P, Massachusetts General Hospital, Boston, MA, Dias, M, Dipartamento di Elettronica, Informazione e Bioingegneria - DEIB, Politecnico di Milano, Collins Fekete, C, Departement de physique, de genie physique et d'optique et Centre de recherche sur le cancer, Universite Laval, Quebec, and Seco, J. 2014. "SU-E-T-550: Range Effects in Proton Therapy Caused by Systematic Errors in the Stoichiometric Calibration". United States. https://doi.org/10.1118/1.4888885.
@article{osti_22369671,
title = {SU-E-T-550: Range Effects in Proton Therapy Caused by Systematic Errors in the Stoichiometric Calibration},
author = {Doolan, P and Massachusetts General Hospital, Boston, MA and Dias, M and Dipartamento di Elettronica, Informazione e Bioingegneria - DEIB, Politecnico di Milano and Collins Fekete, C and Departement de physique, de genie physique et d'optique et Centre de recherche sur le cancer, Universite Laval, Quebec and Seco, J},
abstractNote = {Purpose: The procedure for proton treatment planning involves the conversion of the patient's X-ray CT from Hounsfield units into relative stopping powers (RSP), using a stoichiometric calibration curve (Schneider 1996). In clinical practice a 3.5% margin is added to account for the range uncertainty introduced by this process and other errors. RSPs for real tissues are calculated using composition data and the Bethe-Bloch formula (ICRU 1993). The purpose of this work is to investigate the impact that systematic errors in the stoichiometric calibration have on the proton range. Methods: Seven tissue inserts of the Gammex 467 phantom were imaged using our CT scanner. Their known chemical compositions (Watanabe 1999) were then used to calculate the theoretical RSPs, using the same formula as would be used for human tissues in the stoichiometric procedure. The actual RSPs of these inserts were measured using a Bragg peak shift measurement in the proton beam at our institution. Results: The theoretical calculation of the RSP was lower than the measured RSP values, by a mean/max error of - 1.5/-3.6%. For all seven inserts the theoretical approach underestimated the RSP, with errors variable across the range of Hounsfield units. Systematic errors for lung (average of two inserts), adipose and cortical bone were - 3.0/-2.1/-0.5%, respectively. Conclusion: There is a systematic underestimation caused by the theoretical calculation of RSP; a crucial step in the stoichiometric calibration procedure. As such, we propose that proton calibration curves should be based on measured RSPs. Investigations will be made to see if the same systematic errors exist for biological tissues. The impact of these differences on the range of proton beams, for phantoms and patient scenarios, will be investigated. This project was funded equally by the Engineering and Physical Sciences Research Council (UK) and Ion Beam Applications (Louvain-La-Neuve, Belgium)},
doi = {10.1118/1.4888885},
url = {https://www.osti.gov/biblio/22369671}, journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 41,
place = {United States},
year = {Sun Jun 01 00:00:00 EDT 2014},
month = {Sun Jun 01 00:00:00 EDT 2014}
}