Strahlentherapie und Onkologie

, Volume 194, Issue 7, pp 664–674 | Cite as

Shorter treatment times reduce the impact of intra-fractional motion

A real-time 4DUS study comparing VMAT vs. step-and-shoot IMRT for prostate cancer
  • Hendrik BallhausenEmail author
  • Minglun Li
  • Ute Ganswindt
  • Claus Belka
Original Article



To evaluate the impact of shorter treatment times on intra-fractional motion of the prostate during external beam radiotherapy.


53 h of intra-fractional motion of the prostate were recorded in real-time by 4D ultrasound (4DUS) during 720 fractions in 28 patients, 14 of which whom treated with step-and-shoot intensity-modulated radiotherapy (IMRT) and 14 of whom were treated with volumetric arc therapy (VMAT).


The average VMAT fraction was recorded for 2 min 43 s and was substantially shorter than the average step-and-shoot IMRT fraction at 6 min 13 s. Average radial displacement of the prostate per fraction was substantially and significantly reduced from 1.31 ± 1.28 mm (n = 357 step-and-shoot IMRT fractions) to 0.96 ± 1.04 mm (n = 363 VMAT fractions), p = 0.00004. Radial, vertical, and longitudinal root-mean-square (r. m. s.) error per fraction was reduced from 1.55 to 1.12 mm (−28%, p < 0.0001), from 1.16 to 0.77 mm (−34%, p < 0.0001), and from 0.79 to 0.56 mm (−29%, p = 0.0002), respectively. Lateral intra-fractional motion was generally small and did not differ significantly. The prostate remained during 95% of fraction time within 4.55 mm of the isocenter in case of step-and-shoot IMRT and within 2.45 mm in case of VMAT. The variance of displacements increased linearly with time, and the rate was the same for both step-and-shoot IMRT and VMAT patients.


The position of the prostate changed less during shorter fractions, limiting fraction-average and end-of-fraction variance. This substantially and significantly reduced the impact of intra-fractional motion during shorter VMAT fractions as compared to longer step-and-shoot IMRT fractions.


Organ motion Ultrasound imaging Volumetric-modulated arc therapy Radiotherapy, intensity-modulated Prostate cancer 

Kürzere Behandlungszeit reduziert den Einfluss intrafraktioneller Bewegung

Eine Echtzeit-4DUS-Studie vergleicht VMAT vs. Step-and-shoot-IMRT beim Prostatakarzinom



Die Studie untersucht den Einfluss kürzerer Behandlungszeiten auf das Ausmaß der intrafraktionellen Bewegung der Prostata während einer Strahlentherapie.


In Echtzeit wurden 53 h intrafraktioneller Bewegung der Prostata mit vierdimensionalem Ultraschall (4DUS) während 720 Fraktionen in 28 Patienten aufgezeichnet. Davon wurden 14 Patienten mit intensitätsmodulierter Strahlentherapie (IMRT) im Step-and-shoot-Verfahren behandelt und 14 Patienten im Volumetric-Arc-Therapy-Protokoll (VMAT).


Die mittlere VMAT-Fraktion wurde für 2 min und 43 s aufgezeichnet und war damit deutlich kürzer als die mittlere Step-and-shoot-IMRT-Fraktion mit 6 min und 13 s. Die mittlere radiale Auslenkung der Prostata pro Fraktion wurde deutlich und signifikant reduziert von 1,31 ± 1,28 mm (357 Step-and-shoot-IMRT-Fraktionen) auf 0,96 ± 1,04 mm (363 VMAT-Fraktionen; p = 0,00004). Radiale, vertikale und longitudinale Root-Mean-Square-Fehler (r. m. s.) pro Fraktion wurden reduziert von 1,55 auf 1,12 mm (−28 %; p < 0,0001) bzw. von 1,16 auf 0,77 mm (−34 %; p < 0,0001) bzw. von 0,79 auf 0,56 mm (−29 %; p = 0,0002). Die laterale intrafraktionelle Bewegung war allgemein klein und unterschied sich nicht signifikant. Die Prostata blieb während der Dauer einer Fraktion zu 95 % innerhalb von 4,55 mm im Falle von Step-and-shoot-IMRT und innerhalb von 2,45 mm im Falle von VMAT. Die Varianz der Verschiebungen nahm linear mit der Behandlungszeit zu, wobei die Steigung bei beiden Protokollen die gleiche war.


Die Prostataposition verändert sich während kürzerer Fraktionen weniger, was die mittlere Varianz und die Varianz am Ende der Fraktion begrenzt. Dies reduziert deutlich und signifikant den Einfluss der intrafraktionellen Bewegung während kürzerer VMAT-Fraktionen im Vergleich zu längeren Step-and-shoot-IMRT-Fraktionen.


Organbewegung Ultraschall Volumetrisch modulierte Arc-Therapie Strahlentherapie, intensitätsmodulierte Prostatakarzinom 


Compliance with ethical guidelines

Conflict of interest

U. Ganswindt and C. Belka have a research cooperation with Elekta AB, Stockholm, Sweden. H. Ballhausen and M. Li declare that they have no competing interests.

Ethical standards

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study formal consent is not required. This article does not contain any studies with animals performed by any of the authors.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Radiation Oncology, University HospitalLMU MunichMunichGermany

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