Abstract
Background
The aim of this study was to investigate if the flattening filter free mode (FFF) of a linear accelerator reduces the excess absolute risk (EAR) for second cancer as compared to the flat beam mode (FF) in simultaneous integrated boost (SIB) radiation therapy of right-sided breast cancer.
Patients and methods
Six plans were generated treating the whole breast to 50.4 Gy and a SIB volume to 63 Gy on CT data of 10 patients: intensity-modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), and a tangential arc VMAT (tVMAT), each with flattening filter and without. The EAR was calculated for the contralateral breast and the lungs from dose–volume histograms (DVH) based on the linear-exponential, the plateau, and the full mechanistic dose–response model. Peripheral low-dose measurements were performed to compare the EAR in more distant regions as the thyroids and the uterus.
Results
FFF reduces the EAR significantly in the contralateral and peripheral organs for tVMAT and in the peripheral organs for VMAT. No reduction was found for IMRT. The lowest EAR for the contralateral breast and lung was achieved with tVMAT FFF, reducing the EAR by 25 % and 29 % as compared to tVMAT FF, and by 44 % to 58 % as compared to VMAT and IMRT in both irradiation modes. tVMAT FFF showed also the lowest peripheral dose corresponding to the lowest EAR in the thyroids and the uterus.
Conclusion
The use of FFF mode allows reducing the EAR significantly when tVMAT is used as the treatment technique. When second cancer risk is a major concern, tVMAT FFF is considered the preferred treatment option in SIB irradiation of right-sided breast cancer.
Zusammenfassung
Zielsetzung
Ziel der Studie war es zu untersuchen, ob der ausgleichskörperfreie Modus (FFF) bei der simultan integrierten Boost-(SIB-)Bestrahlung des rechtsseitigen Mammakarzinoms eine Reduktion des strahleninduzierten Sekundärmalignomrisikos („excess absolute risk“, EAR) im Vergleich zur Bestrahlung mit Ausgleichskörper (FF) erlaubt.
Patienten und Methoden
Auf CT-Daten von 10 Patienten wurden jeweils 6 Pläne zur Behandlung der gesamten Brust mit einer Verschreibungsdosis von 50,4 Gy und eines SIB mit 63 Gy generiert: eine intensitätsmodulierte Strahlentherapie (IMRT), eine volumenmodulierte Rotationstherapie (VMAT) und eine tangentiale VMAT (tVMAT), jeweils mit und ohne Ausgleichskörper. Das EAR wurde für die kontralaterale Brust und die Lungen anhand des linear-exponentiellen Modells, des Plateau- und des mechanistischen Modells für die Dosisreaktion aus den Dosis-Volumen-Histogrammen (DVH) der Organe berechnet. Zusätzlich wurden periphere Dosismessungen durchgeführt, um das EAR in Schilddrüse und Uterus zu vergleichen.
Ergebnisse
FFF reduziert das EAR in den kontralateralen und peripheren Risikoorganen bei tVMAT und in den peripheren Organen bei VMAT. Bei IMRT konnte keine Reduktion beobachtet werden. Das signifikant niedrigste EAR für die kontralaterale Brust und Lunge wurde mit tVMAT FFF erreicht, mit einer Reduktion um 25 % bzw. 29 % im Vergleich zu tVMAT FF und um 44–58 % im Vergleich zu VMAT und IMRT in beiden Modi. Das niedrigste EAR in Schilddrüse und Uterus wurde ebenfalls mit tVMAT FFF erreicht.
Schlussfolgerung
Der ausgleichskörperfreie Modus eines Linearbeschleunigers erlaubt eine signifikante Reduktion des EAR, wenn zugleich tVMAT als Bestrahlungstechnik gewählt wird. Daher wird tVMAT FFF als bevorzugte Bestrahlungsoption betrachtet, wenn das Sekundärmalignomrisiko von großer Bedeutung ist.
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Abbreviations
- 3D-CRT:
-
three-dimensional conformal radiation therapy
- DVH:
-
dose–volume histogram
- EAR:
-
excess absolute risk
- FF:
-
flattening filter
- FFF:
-
flattening filter free
- IMRT:
-
intensity-modulated radiation therapy
- lin:
-
linear model
- lin_exp:
-
linear–exponential model
- mech:
-
full mechanistic model
- OAR:
-
organ at risk
- OED:
-
organ equivalent dose
- plateau:
-
plateau model
- PTV:
-
planning target volume
- SIB:
-
simultaneous integrated boost
- VMAT:
-
volumetric modulated arc therapy
- tVMAT:
-
tangential volumetric modulated arc therapy
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Funding
This study was funded by the Bavarian State Ministry of the Environment and Consumer Protection.
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The department has research cooperation with Elekta GmbH Hamburg. B. Dobler, J. Maier, B. Knott, M. Maerz, R. Loeschel, and O. Koebl declare that they have no competing interests.
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Dobler, B., Maier, J., Knott, B. et al. Second Cancer Risk after simultaneous integrated boost radiation therapy of right sided breast cancer with and without flattening filter. Strahlenther Onkol 192, 687–695 (2016). https://doi.org/10.1007/s00066-016-1025-5
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DOI: https://doi.org/10.1007/s00066-016-1025-5