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Inclined head position improves dose distribution during hippocampal-sparing whole brain radiotherapy using VMAT

Schräge Kopfposition bessert die Dosisverteilung bei der hippokampusschonenden Ganzhirnbestrahlung mit VMAT

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Abstract

Purpose

Hippocampal-sparing whole brain radiotherapy (HS-WBRT) aims to preserve neurocognitive functions in patients undergoing brain radiotherapy (RT). Volumetric modulated arc therapy (VMAT) involves intensity-modulated RT using a coplanar arc. An inclined head position might improve dose distribution during HS-WBRT using VMAT.

Materials and methods

This study analyzed 8 patients receiving brain RT with inclined head positioning. A comparable set of CT images simulating a non-inclined head position was obtained by rotating the original CT set. HS-WBRT plans of coplanar VMAT for each CT set were generated with a prescribed dose of 30 Gy in 10 fractions. Maximum dose to the hippocampi was limited to 16 Gy; to the optic nerve, optic chiasm, and eyeballs this was confined to less than 37.5 Gy; for the lenses to 8 Gy. Dosimetric parameters of the two different plans of 8 patients were compared with paired t-test.

Results

Mean inclined head angle was 11.09 ± 0.73°. The homogeneity (HI) and conformity (CI) indexes demonstrated improved results, with an average 8.4 ± 10.0 % (p = 0.041) and 5.3 ± 3.9 % (p = 0.005) reduction, respectively, in the inclined vs. non-inclined position. The inclined head position had lower hippocampi Dmin (10.45 ± 0.36 Gy), Dmax (13.70 ± 0.25 Gy), and Dmean (12.01 ± 0.38 Gy) values vs. the non-inclined head position (Dmin = 12.07 ± 1.07 Gy; Dmax = 15.70 ± 1.25 Gy; Dmean = 13.91 ± 1.01 Gy), with 12.8 ± 8.9 % (p = 0.007), 12.2 ± 6.8 % (p = 0.003), and 13.2 ± 7.2 % (p = 0.002) reductions, respectively. Mean Dmax for the lenses was 6.34 ± 0.72 Gy and 7.60 ± 0.46 Gy, respectively, with a 16.3 ± 10.8 % reduction in the inclined position (p = 0.004). Dmax for the optic nerve and Dmean for the eyeballs also decreased by 7.0 ± 5.9 % (p = 0.015) and 8.4 ± 7.2 % (p = 0.015), respectively.

Conclusion

Inclining the head position to approximately 11° during HS-WBRT using VMAT improved dose distribution in the planning target volume and allowed lower doses to the hippocampi and optic apparatus.

Zusammenfassung

Zielsetzung

Die hippokampusschonende Ganzhirnbestrahlung (HS-WBRT) schützt die neurokognitiven Funktionen der Patienten. Die volumenmodulierte Arc-Therapie (VMAT) ist eine intensitätsmodulierte Strahlentherapie (IMRT) mit koplanarer Achse. Eine schräge Kopfhaltung könnte die Dosisverteilung während der HS-WBRT mit VMAT verbessern.

Material und Methode

Untersucht wurden 8 Patienten mit einer WBRT in geneigter Kopfhaltung. Durch Rotation der Original-CT-Datensätze wurden vergleichbare CT-Datensätze mit nicht geneigtem Kopf simulierten. Die HS-WBRT-Pläne mit koplanarer VMAT enthielten für jeden CT-Datensatz eine vorgeschriebene Dosis von 30 Gy in 10 Fraktionen. Die maximale Dosierung des Hippokampus war auf 17 Gy, für Sehnerv, Sehnervenkreuzung und Augapfel war die Dosierung auf 37,5 Gy und für Linsen auf 8 Gy begrenzt. Dosimetrische Parameter der beiden unterschiedlichen Planungen der 5 Patienten wurden mit dem gepaarten t-Test verglichen.

Ergebnisse

Der Mittelwert des Neigungswinkels betrug 11,09 ± 0,73°. Bei geneigtem Kopf sanken der Homogenitäts- und Konformitätsindex um durchschnittlich je 8,4 ± 10,0 % (p = 0,041) bzw. 5,3 ± 3,9 % (p = 0,005). Im Hippokampus ergab ein geneigter Kopf niedrigere Werte von Dmin (10,45 ± 0,36 Gy), Dmax (13,7 ± 0,25 Gy) und Dmean (12,01 ± 0,38 Gy) als ein nichtgeneigter Kopf (Dmin 12,07 ± 1,07 Gy; Dmax 15,70 ± 1,25 Gy; Dmean 13,91 ± 1,01 Gy) mit einer Reduktion von jeweils 12,8 ± 8,9 % (p = 0,007), 12,2 ± 6,8 % (p = 0,003) und 13,2 ± 7,2 % (p = 0,002). Die Dmax der Linsen betrug bei Behandlungen mit geneigtem Kopf 6,34 ± 0,72 Gy und 7,60 ± 0,46 (Rückgang um 16,3 ± 10,8 %; p = 0,004). Dmax für Sehnerven und Dmean für Augäpfel sanken ebenfalls um 7,0 ± 5,9 % (p = 0,015) bzw. 8,4 ± 7,2 % (p = 0,015).

Schlussfolgerung

Die HS-WBRT mit VMAT mit ca. 11° geneigtem Kopf führt im Vergleich zum gerade positionierten Kopf zu einer besseren PTV-Dosisverteilung und reduziert die Dosisbelastung in Hippokampus und optischen Sehorganen.

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Acknowledgements

This work was supported by the grant (#0820010) for Cancer Control Program from Korean Ministry of Health & Welfare to In Ah Kim.

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Authors and Affiliations

  1. Departments of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea

    Kyung Su Kim MD, Suk-Jin Seo BS, Jaegi Lee BS, Eunji Kim MD, Noorie Choi MD, Keun-Yong Eom MD, PhD, Jae-Sung Kim MD, PhD & In Ah Kim MD, PhD

  2. Department of Radiation Oncology, Seoul National University Bundang Hospital, 166 Gumiro, 13620, Seongnamsi, Kyeonggido, Republic of Korea

    Jin-Yong Seok CMD, Joo Wan Hong BS, Jin-Beom Chung PhD, Keun-Yong Eom MD, PhD, Jae-Sung Kim MD, PhD & In Ah Kim MD, PhD

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  1. Kyung Su Kim MD
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Correspondence to In Ah Kim MD, PhD.

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Conflict of interest

K.S. Kim, S.-J. Seo, J. Lee, J.-Y. Seok, J.W. Hong, J.-B. Chung, E. Kim, N. Choi, K.-Y. Eom, J.-S. Kim and I.A. Kim state that there are no conflicts of interest.

Ethical standards

All studies on humans described in the present manuscript were carried out with the approval of the responsible ethics committee and in accordance with national law and the Helsinki Declaration of 1975 (in its current, revised form). Informed consent was obtained from all patients included in studies.

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Kim, K.S., Seo, SJ., Lee, J. et al. Inclined head position improves dose distribution during hippocampal-sparing whole brain radiotherapy using VMAT. Strahlenther Onkol 192, 473–480 (2016). https://doi.org/10.1007/s00066-016-0973-0

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