Hounsfield units variations: Impact on CT-density based conversion tables and their effects on dose distribution

B. Zurl; R. Tiefling; P. Winkler; Peter Kindl; K.S. Kapp

doi:10.1007/s00066-013-0464-5

Hounsfield units variations: Impact on CT-density based conversion tables and their effects on dose distribution

Titel in Übersetzung: Schwankungen der Hounsfield-Einheiten: Auswirkung von CT-dichtebasierten Konversionstabellen und ihr Einfluss auf Dosisverteilungen

B. Zurl^*
, R. Tiefling
, P. Winkler
, Peter Kindl
, K.S. Kapp

^*Korrespondierende/r Autor/-in für diese Arbeit

Institut für Materialphysik (5170)

Publikation: Beitrag in einer Fachzeitschrift › Artikel › Begutachtung

Abstract

Hintergrund
Bestimmung von Dosisunsicherheiten in der Bestrahlungsplanung durch Schwankungen der Hounsfield-Einheiten (HU) bei Verwendung unterschiedlicher CT-Protokolle.
Patienten und Methoden
Anhand unterschiedlicher klinisch verwendeter CT-Scan-Protokolle wurden Konversionstabellen zur Dosisberechnung erstellt und im Phantom getestet. Unter Zuhilfenahme dieser Tabellen wurden 28 reale Bestrahlungspläne nachgerechnet, nachdem bei diesen Patienten irrtümlich ein ungeeignetes Scan-Protokoll verwendet worden war.
Ergebnisse
Unterschiedliche CT-Einstellungsparameter zeigten für Dichten < 1,1 g/cm3 HU-Schwankungen bis zu 2,6 %, bei Dichten > 1,1 g/cm3 jedoch Abweichungen bis zu 25,6 %. Die größten Schwankungen traten bei Änderung der Röhrenspannung auf. Untersuchungen am virtuellen Wasserphantom mit Schichten unterschiedlicher Dicke und Dichte zeigten einen sägezahnartigen Anstieg der Dosisänderungen von 0,3%, 0,6% und 1,5 % bei Schichtstärken von 1, 3 und 7 cm. Bei Verwendung eines „Beam-hardening“-Filters resultierte bei einer Dichteänderung von 5 % eine Referenzdosisänderung von 0,6 %. Die Rekalkulation von 28 Patienten mit Bestrahlungen im Schädelbereich zeigte bei Verwendung der korrekten Konversionstabelle eine Überdosierung im Knochenbereich von 1,3 ± 0,4 % und im Bereich der Gehirnmasse von 0,7 ± 0,1 %. Im Mittel wurde somit zusätzlich eine Monitoreinheit (Spanne 0–3 MU) pro 100 MU verabreicht.
Schlussfolgerung
Die Verwendung verschiedener CT-Scan-Protokolle führt zu HU-Abweichungen von bis zu 20 %. Dies kann einen mittleren systematischen Dosisfehler von 1,5 % verursachen. Spezifische Konversionstabellen und automatische CT-Protokollerkennung könnten Dosisungenauigkeiten dieser Art reduzieren.

Titel in Übersetzung	Schwankungen der Hounsfield-Einheiten: Auswirkung von CT-dichtebasierten Konversionstabellen und ihr Einfluss auf Dosisverteilungen
Originalsprache	englisch
Seiten (von - bis)	88-93
Fachzeitschrift	Strahlentherapie und Onkologie
Jahrgang	190
Ausgabenummer	1
DOIs	https://doi.org/10.1007/s00066-013-0464-5
Publikationsstatus	Veröffentlicht - 2013

Fields of Expertise

Advanced Materials Science

Treatment code (Nähere Zuordnung)

Basic - Fundamental (Grundlagenforschung)

Zugriff auf Dokument

10.1007/s00066-013-0464-5

Strahlenphysik
Rabitsch, H. (Sonstige Funktion), Kindl, P. (Projektleiter), Beck, P. (Sonstige Funktion) & Ninaus, W. (Sonstige Funktion)
1/01/95 → 31/01/13
Projekt: Arbeitsgebiet

Dieses zitieren

@article{be5907e11e5c4c0998342d9935c4c256,

title = "Hounsfield units variations: Impact on CT-density based conversion tables and their effects on dose distribution",

abstract = "Purpose Determination of dose error margins in radiation therapy planning due to variations in Hounsfield Units (HU) values dependent on the use of different CT scanning protocols. Patients and methods Based on a series of different CT scanning protocols used in clinical practice, conversion tables for radiation dose calculations were generated and subsequently tested on a phantom. These tables were then used to recalculate the radiation therapy plans of 28 real patients after an incorrect scanning protocol had inadvertently been used for these patients. Results Different CT parameter settings resulted in errors of HU values of up to 2.6 \% for densities of < 1.1 g/cm3, but up to 25.6 \% for densities of > 1.1 g/cm3. The largest errors were associated with changes in the tube voltage. Tests on a virtual water phantom with layers of variable thickness and density revealed a sawtooth-shaped curve for the increase of dose differences from 0.3 to 0.6 \% and 1.5 \% at layer thicknesses of 1, 3, and 7 cm, respectively. Use of a beam hardening filter resulted in a reference dose difference of 0.6 \% in response to a density change of 5 \%. The recalculation of data from 28 patients who received radiation therapy to the head revealed an overdose of 1.3 ± 0.4 \% to the bone and 0.7 ± 0.1 \% to brain tissue. On average, therefore, one monitor unit (range 0{\textendash}3 MU) per 100 MU more than the correct dose had been given. Conclusion Use of different CT scanning protocols leads to variations of up to 20 \% in the HU values. This can result in a mean systematic dose error of 1.5 \%. Specific conversion tables and automatic CT scanning protocol recognition could reduce dose errors of these types.",

author = "B. Zurl and R. Tiefling and P. Winkler and Peter Kindl and K.S. Kapp",

year = "2013",

doi = "10.1007/s00066-013-0464-5",

language = "English",

volume = "190",

pages = "88--93",

journal = "Strahlentherapie und Onkologie",

issn = "1439-099X",

publisher = "Springer Science and Business Media Deutschland GmbH",

number = "1",

}

TY - JOUR

T1 - Hounsfield units variations

T2 - Impact on CT-density based conversion tables and their effects on dose distribution

AU - Zurl, B.

AU - Tiefling, R.

AU - Winkler, P.

AU - Kindl, Peter

AU - Kapp, K.S.

PY - 2013

Y1 - 2013

N2 - Purpose Determination of dose error margins in radiation therapy planning due to variations in Hounsfield Units (HU) values dependent on the use of different CT scanning protocols. Patients and methods Based on a series of different CT scanning protocols used in clinical practice, conversion tables for radiation dose calculations were generated and subsequently tested on a phantom. These tables were then used to recalculate the radiation therapy plans of 28 real patients after an incorrect scanning protocol had inadvertently been used for these patients. Results Different CT parameter settings resulted in errors of HU values of up to 2.6 % for densities of < 1.1 g/cm3, but up to 25.6 % for densities of > 1.1 g/cm3. The largest errors were associated with changes in the tube voltage. Tests on a virtual water phantom with layers of variable thickness and density revealed a sawtooth-shaped curve for the increase of dose differences from 0.3 to 0.6 % and 1.5 % at layer thicknesses of 1, 3, and 7 cm, respectively. Use of a beam hardening filter resulted in a reference dose difference of 0.6 % in response to a density change of 5 %. The recalculation of data from 28 patients who received radiation therapy to the head revealed an overdose of 1.3 ± 0.4 % to the bone and 0.7 ± 0.1 % to brain tissue. On average, therefore, one monitor unit (range 0–3 MU) per 100 MU more than the correct dose had been given. Conclusion Use of different CT scanning protocols leads to variations of up to 20 % in the HU values. This can result in a mean systematic dose error of 1.5 %. Specific conversion tables and automatic CT scanning protocol recognition could reduce dose errors of these types.

AB - Purpose Determination of dose error margins in radiation therapy planning due to variations in Hounsfield Units (HU) values dependent on the use of different CT scanning protocols. Patients and methods Based on a series of different CT scanning protocols used in clinical practice, conversion tables for radiation dose calculations were generated and subsequently tested on a phantom. These tables were then used to recalculate the radiation therapy plans of 28 real patients after an incorrect scanning protocol had inadvertently been used for these patients. Results Different CT parameter settings resulted in errors of HU values of up to 2.6 % for densities of < 1.1 g/cm3, but up to 25.6 % for densities of > 1.1 g/cm3. The largest errors were associated with changes in the tube voltage. Tests on a virtual water phantom with layers of variable thickness and density revealed a sawtooth-shaped curve for the increase of dose differences from 0.3 to 0.6 % and 1.5 % at layer thicknesses of 1, 3, and 7 cm, respectively. Use of a beam hardening filter resulted in a reference dose difference of 0.6 % in response to a density change of 5 %. The recalculation of data from 28 patients who received radiation therapy to the head revealed an overdose of 1.3 ± 0.4 % to the bone and 0.7 ± 0.1 % to brain tissue. On average, therefore, one monitor unit (range 0–3 MU) per 100 MU more than the correct dose had been given. Conclusion Use of different CT scanning protocols leads to variations of up to 20 % in the HU values. This can result in a mean systematic dose error of 1.5 %. Specific conversion tables and automatic CT scanning protocol recognition could reduce dose errors of these types.

U2 - 10.1007/s00066-013-0464-5

DO - 10.1007/s00066-013-0464-5

M3 - Article

SN - 1439-099X

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JO - Strahlentherapie und Onkologie

JF - Strahlentherapie und Onkologie

IS - 1

ER -

Hounsfield units variations: Impact on CT-density based conversion tables and their effects on dose distribution

Abstract

Fields of Expertise

Treatment code (Nähere Zuordnung)

Zugriff auf Dokument

Fingerprint

Projekte

Strahlenphysik

Dieses zitieren