Consensus guide on CT-based prediction of stopping-power ratio using a Hounsfield look-up table for proton therapy

Nils Peters; Vicki Trier Taasti; Benjamin Ackermann; Alessandra Bolsi; Christina Vallhagen Dahlgren; Malte Ellerbrock; Francesco Fracchiolla; Carles Goma; Joanna Gora; Patricia Cambraia Lopes; Ilaria Rinaldi; Koen Salvo; Ivanka Sojat Tarp; Alessandro Vai; Thomas Bortfeld; Antony Lomax; Christian Richter; Patrick Wohlfahrt

doi:10.1016/j.radonc.2023.109675

Consensus guide on CT-based prediction of stopping-power ratio using a Hounsfield look-up table for proton therapy

Nils Peters^*, Vicki Trier Taasti^*, Benjamin Ackermann, Alessandra Bolsi, Christina Vallhagen Dahlgren, Malte Ellerbrock, Francesco Fracchiolla, Carles Goma, Joanna Gora, Patricia Cambraia Lopes, Ilaria Rinaldi, Koen Salvo, Ivanka Sojat Tarp, Alessandro Vai, Thomas Bortfeld, Antony Lomax, Christian Richter, Patrick Wohlfahrt

^*Corresponding author for this work

GROW - Innovative Cancer Diagnostics & Therapy

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

Background and purpose: Studies have shown large variations in stopping-power ratio (SPR) prediction from computed tomography (CT) across European proton centres. To standardise this process, a step-by-step guide on specifying a Hounsfield look-up table (HLUT) is presented here.Materials and methods: The HLUT specification process is divided into six steps: Phantom setup, CT acqui-sition, CT number extraction, SPR determination, HLUT specification, and HLUT validation. Appropriate CT phantoms have a head-and body-sized part, with tissue-equivalent inserts in regard to X-ray and proton interactions. CT numbers are extracted from a region-of-interest covering the inner 70% of each insert in -plane and several axial CT slices in scan direction. For optimal HLUT specification, the SPR of phantom inserts is measured in a proton beam and the SPR of tabulated human tissues is computed stoichiomet-rically at 100 MeV. Including both phantom inserts and tabulated human tissues increases HLUT stability. Piecewise linear regressions are performed between CT numbers and SPRs for four tissue groups (lung, adipose, soft tissue, and bone) and then connected with straight lines. Finally, a thorough but simple val-idation is performed.Results: The best practices and individual challenges are explained comprehensively for each step. A well-defined strategy for specifying the connection points between the individual line segments of the HLUT is presented. The guide was tested exemplarily on three CT scanners from different vendors, prov-ing its feasibility.Conclusion: The presented step-by-step guide for CT-based HLUT specification with recommendations and examples can contribute to reduce inter-centre variations in SPR prediction.(c) 2023 The Authors. Published by Elsevier B.V. Radiotherapy and Oncology 184 (2023) 1-7 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Original language	English
Article number	109675
Number of pages	7
Journal	Radiotherapy and Oncology
Volume	184
Issue number	1
Early online date	1 May 2023
DOIs	https://doi.org/10.1016/j.radonc.2023.109675
Publication status	Published - 1 Jul 2023

Keywords

Hounsfield look -up table
Proton therapy
Single -energy CT
Stoichiometric calibration
Stopping -power ratio
Proton range prediction
EXPERIMENTAL-VERIFICATION
RANGE UNCERTAINTIES
CALIBRATION

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10.1016/j.radonc.2023.109675Licence: CC BY-NC-ND

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Peters, N., Taasti, V. T., Ackermann, B., Bolsi, A., Dahlgren, C. V., Ellerbrock, M., Fracchiolla, F., Goma, C., Gora, J., Lopes, P. C., Rinaldi, I., Salvo, K., Tarp, I. S., Vai, A., Bortfeld, T., Lomax, A., Richter, C., & Wohlfahrt, P. (2023). Consensus guide on CT-based prediction of stopping-power ratio using a Hounsfield look-up table for proton therapy. Radiotherapy and Oncology, 184(1), Article 109675. https://doi.org/10.1016/j.radonc.2023.109675

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abstract = "Background and purpose: Studies have shown large variations in stopping-power ratio (SPR) prediction from computed tomography (CT) across European proton centres. To standardise this process, a step-by-step guide on specifying a Hounsfield look-up table (HLUT) is presented here.Materials and methods: The HLUT specification process is divided into six steps: Phantom setup, CT acqui-sition, CT number extraction, SPR determination, HLUT specification, and HLUT validation. Appropriate CT phantoms have a head-and body-sized part, with tissue-equivalent inserts in regard to X-ray and proton interactions. CT numbers are extracted from a region-of-interest covering the inner 70% of each insert in -plane and several axial CT slices in scan direction. For optimal HLUT specification, the SPR of phantom inserts is measured in a proton beam and the SPR of tabulated human tissues is computed stoichiomet-rically at 100 MeV. Including both phantom inserts and tabulated human tissues increases HLUT stability. Piecewise linear regressions are performed between CT numbers and SPRs for four tissue groups (lung, adipose, soft tissue, and bone) and then connected with straight lines. Finally, a thorough but simple val-idation is performed.Results: The best practices and individual challenges are explained comprehensively for each step. A well-defined strategy for specifying the connection points between the individual line segments of the HLUT is presented. The guide was tested exemplarily on three CT scanners from different vendors, prov-ing its feasibility.Conclusion: The presented step-by-step guide for CT-based HLUT specification with recommendations and examples can contribute to reduce inter-centre variations in SPR prediction.(c) 2023 The Authors. Published by Elsevier B.V. Radiotherapy and Oncology 184 (2023) 1-7 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).",

keywords = "Hounsfield look -up table, Proton therapy, Single -energy CT, Stoichiometric calibration, Stopping -power ratio, Proton range prediction, EXPERIMENTAL-VERIFICATION, RANGE UNCERTAINTIES, CALIBRATION",

author = "Nils Peters and Taasti, {Vicki Trier} and Benjamin Ackermann and Alessandra Bolsi and Dahlgren, {Christina Vallhagen} and Malte Ellerbrock and Francesco Fracchiolla and Carles Goma and Joanna Gora and Lopes, {Patricia Cambraia} and Ilaria Rinaldi and Koen Salvo and Tarp, {Ivanka Sojat} and Alessandro Vai and Thomas Bortfeld and Antony Lomax and Christian Richter and Patrick Wohlfahrt",

year = "2023",

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doi = "10.1016/j.radonc.2023.109675",

language = "English",

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journal = "Radiotherapy and Oncology",

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Peters, N, Taasti, VT, Ackermann, B, Bolsi, A, Dahlgren, CV, Ellerbrock, M, Fracchiolla, F, Goma, C, Gora, J, Lopes, PC, Rinaldi, I, Salvo, K, Tarp, IS, Vai, A, Bortfeld, T, Lomax, A, Richter, C & Wohlfahrt, P 2023, 'Consensus guide on CT-based prediction of stopping-power ratio using a Hounsfield look-up table for proton therapy', Radiotherapy and Oncology, vol. 184, no. 1, 109675. https://doi.org/10.1016/j.radonc.2023.109675

TY - JOUR

T1 - Consensus guide on CT-based prediction of stopping-power ratio using a Hounsfield look-up table for proton therapy

AU - Peters, Nils

AU - Taasti, Vicki Trier

AU - Ackermann, Benjamin

AU - Bolsi, Alessandra

AU - Dahlgren, Christina Vallhagen

AU - Ellerbrock, Malte

AU - Fracchiolla, Francesco

AU - Goma, Carles

AU - Gora, Joanna

AU - Lopes, Patricia Cambraia

AU - Rinaldi, Ilaria

AU - Salvo, Koen

AU - Tarp, Ivanka Sojat

AU - Vai, Alessandro

AU - Bortfeld, Thomas

AU - Lomax, Antony

AU - Richter, Christian

AU - Wohlfahrt, Patrick

PY - 2023/7/1

Y1 - 2023/7/1

N2 - Background and purpose: Studies have shown large variations in stopping-power ratio (SPR) prediction from computed tomography (CT) across European proton centres. To standardise this process, a step-by-step guide on specifying a Hounsfield look-up table (HLUT) is presented here.Materials and methods: The HLUT specification process is divided into six steps: Phantom setup, CT acqui-sition, CT number extraction, SPR determination, HLUT specification, and HLUT validation. Appropriate CT phantoms have a head-and body-sized part, with tissue-equivalent inserts in regard to X-ray and proton interactions. CT numbers are extracted from a region-of-interest covering the inner 70% of each insert in -plane and several axial CT slices in scan direction. For optimal HLUT specification, the SPR of phantom inserts is measured in a proton beam and the SPR of tabulated human tissues is computed stoichiomet-rically at 100 MeV. Including both phantom inserts and tabulated human tissues increases HLUT stability. Piecewise linear regressions are performed between CT numbers and SPRs for four tissue groups (lung, adipose, soft tissue, and bone) and then connected with straight lines. Finally, a thorough but simple val-idation is performed.Results: The best practices and individual challenges are explained comprehensively for each step. A well-defined strategy for specifying the connection points between the individual line segments of the HLUT is presented. The guide was tested exemplarily on three CT scanners from different vendors, prov-ing its feasibility.Conclusion: The presented step-by-step guide for CT-based HLUT specification with recommendations and examples can contribute to reduce inter-centre variations in SPR prediction.(c) 2023 The Authors. Published by Elsevier B.V. Radiotherapy and Oncology 184 (2023) 1-7 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

AB - Background and purpose: Studies have shown large variations in stopping-power ratio (SPR) prediction from computed tomography (CT) across European proton centres. To standardise this process, a step-by-step guide on specifying a Hounsfield look-up table (HLUT) is presented here.Materials and methods: The HLUT specification process is divided into six steps: Phantom setup, CT acqui-sition, CT number extraction, SPR determination, HLUT specification, and HLUT validation. Appropriate CT phantoms have a head-and body-sized part, with tissue-equivalent inserts in regard to X-ray and proton interactions. CT numbers are extracted from a region-of-interest covering the inner 70% of each insert in -plane and several axial CT slices in scan direction. For optimal HLUT specification, the SPR of phantom inserts is measured in a proton beam and the SPR of tabulated human tissues is computed stoichiomet-rically at 100 MeV. Including both phantom inserts and tabulated human tissues increases HLUT stability. Piecewise linear regressions are performed between CT numbers and SPRs for four tissue groups (lung, adipose, soft tissue, and bone) and then connected with straight lines. Finally, a thorough but simple val-idation is performed.Results: The best practices and individual challenges are explained comprehensively for each step. A well-defined strategy for specifying the connection points between the individual line segments of the HLUT is presented. The guide was tested exemplarily on three CT scanners from different vendors, prov-ing its feasibility.Conclusion: The presented step-by-step guide for CT-based HLUT specification with recommendations and examples can contribute to reduce inter-centre variations in SPR prediction.(c) 2023 The Authors. Published by Elsevier B.V. Radiotherapy and Oncology 184 (2023) 1-7 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

KW - Hounsfield look -up table

KW - Proton therapy

KW - Single -energy CT

KW - Stoichiometric calibration

KW - Stopping -power ratio

KW - Proton range prediction

KW - EXPERIMENTAL-VERIFICATION

KW - RANGE UNCERTAINTIES

KW - CALIBRATION

U2 - 10.1016/j.radonc.2023.109675

DO - 10.1016/j.radonc.2023.109675

M3 - Article

C2 - 37084884

SN - 0167-8140

VL - 184

JO - Radiotherapy and Oncology

JF - Radiotherapy and Oncology

IS - 1

M1 - 109675

ER -