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Comparison of CT-number parameterization models for stoichiometric CT calibration in proton therapy
Stockholm University, Faculty of Science, Department of Physics. Karolinska University Hospital, Sweden.
Number of Authors: 32018 (English)In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 47, p. 42-49Article in journal (Refereed) Published
Abstract [en]

Purpose: This study compares the predictions of three parameterization models used in previously published works, implementing the stoichiometric CT calibration for proton therapy, and a further two alternative parameterizations suggested here. Methods: Stoichiometric calibrations of patient CT-number to stopping-power ratio (SPR) were performed for four CT protocols using tissue substitutes supplied by CIRS (CIRS Inc., Norfolk, VA, USA). To evaluate robustness of the five models (Sch96/Sch00/Mar12/Karol/Spek), the calibration was repeatedly simulated by randomly perturbing the measured CT-numbers of the tissue substitutes (1 sigma:10HU). The impact of high-Z content was assessed through calibrations where the two substitutes with barium content were replaced by hypothetical materials without barium. Results: The stoichiometric calibrations generally agreed within 1% between the models, for non-bony tissues. For higher CT-numbers, a well-known 2-parameter model (Sch00) generated larger SPRs compared to the other models, with inter-model discrepancies of up to 3%. The 95% coverage interval of the calibrations obtained from the robustness analysis varied substantially. The well-known 2- and 3-parameter models (Sch00/Sch96) had the largest intervals. However, the partly-hypothetical (i.e. no barium) input data generated calibrations that agreed within 1% over the whole CT scale for all models and improved the 95% coverage interval of the well-known models (Sch00/Sch96). Conclusion: All parameterization models performed comparably if the scanned materials only contained elements with Z <= 20. However, the two alternative models proposed here (Karol/Spek), together with a previously published 1-parameter model (Mar12), generated robust calibrations in close agreement even when tissue substitutes contain elements with higher atomic number.

Place, publisher, year, edition, pages
2018. Vol. 47, p. 42-49
Keywords [en]
CT calibration, Stoichiometric method, Stopping-power ratios, Proton therapy
National Category
Physical Sciences Cancer and Oncology
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-156128DOI: 10.1016/j.ejmp.2018.02.016ISI: 000428926700006PubMedID: 29609817OAI: oai:DiVA.org:su-156128DiVA, id: diva2:1203355
Available from: 2018-05-03 Created: 2018-05-03 Last updated: 2018-05-03Bibliographically approved

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