Abstract
Objective
Current constraints aim to minimize the risk of radiation myelitis by the use of restrictive maximal spinal cord doses, commonly 50 Gy. However, several studies suggested that a dose–volume effect could exist. Based on these observations, we evaluated patients receiving potentially excessive doses to the spinal cord within minimal volumes.
Patients and methods
Patients receiving radiotherapy between June 2010 and May 2015 using the NovalisTM (Varian, Palo Alto, CA, USA; Brainlab, Heimstetten, Germany) radiosurgery system were retrospectively analyzed. A total of 56 patients with 62 treated lesions that had been prescribed radiation doses close to the spinal cord potentially higher than the common 50 Gy 2‑Gy equivalent-dose (EQD2) constraint were selected for further analysis. Of these patients, 26 with 31 lesions had no history of previous irradiation, while 30 patients with 31 lesions had been previously irradiated within the treatment field.
Results
According to different dose evaluation approaches (spinal canal, spinal cord contour), 16 and 10 out of 31 primary irradiated lesions infringed constraints. For the 16 lesions violating spinal canal doses, the maximum doses ranged from 50.5 to 61.9 Gy EQD2. Reirradiated lesions had an average and median cumulative dose of 70.5 and 69 Gy, respectively. Dose drop-off was steep in both groups. Median overall survival was 17 months. No radiation myelitis or radiomorphological alterations were observed during follow-up.
Conclusion
This study adds to the increasing body of evidence indicating that excessive spinal cord doses within a minimal volume, especially in a reirradiation setting with topographically distinct high-point doses, may be given to patients after careful evaluation of treatment- and tumor-associated risks.
Zusammenfassung
Zielsetzung
Um das Risiko einer radiogenen Myelitis zu minimieren, sind klinisch gebräuchliche Dosisobergrenzen für das Rückenmark mit 50-Gy-Maximaldosis sehr restriktiv. Einige Veröffentlichungen deuten jedoch darauf hin, dass ein Dosis-Volumen-Effekt besteht. Unter diesem Aspekt wurden Patienten ausgewertet, die kleinstvolumig mit potenziell überhöhten Rückenmarksdosen bestrahlt wurden.
Patienten
Retrospektiv ausgewertet wurden Patienten, die zwischen Juni 2010 und Mai 2015 mit dem NovalisTM-Radiochirurgiesystem (Varian, Paulo Alto, CA, USA; Brainlab, Heimstetten, Deutschland) behandelt wurden. Für weitere Analysen wurden 62 Läsionen bei 56 Patienten mit potenziell überhöhter Rückenmarksdosis (>50 Gy), berechnet als 2‑Gy-Äquivalenzdosis (EQD2), ausgewählt. Von diesen waren 26 Patienten mit 31 Läsionen ohne Vorbestrahlung und 30 Patienten mit 31 Läsionen bereits im gleichen Bereich vorbestrahlt.
Ergebnisse
Unter Verwendung verschiedener Dosisevaluationsverfahren (Spinalkanal, minimal konturierter Rückenmarksbereich) überschritten 16 und 10 der 31 erstmalig bestrahlten Läsionen die Grenze. Bei den 16, die Maximaldosis überschreitenden Läsionen lag die maximale Myelondosis zwischen 50,5 und 61,9 Gy EQD2. Wiederbestrahlte Läsionen hatten eine durchschnittliche/mediane Kumulativdosis von 70,5 und 69 Gy. Der Dosisabfall war in beiden Gruppen sehr steil. Das mediane Gesamtüberleben betrug 17 Monate. Während der Nachsorge wurden keine radiogene Myelitis oder röntgenmorphologische Veränderungen beobachtet.
Schlussfolgerung
Die Studie liefert Hinweise darauf, dass nach sorgsamem Abwägen von Behandlungs- und tumorassoziierten Risiken eine kleinstvolumige Überdosierung des Myelons in Einzelfällen möglich erscheint, insbesondere bei Rebestrahlung mit topographisch unterschiedlich lokalisierten Maximaldosen.
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S. Zschaeck, P. Wust, R. Graf, W. Wlodarczyk, R. Schild, A.H. Thieme, M. Weihrauch, V. Budach, and P. Ghadjar declare that they have no competing interests.
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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. Evaluation of the data was approved by the Institutional Ethics Committee.
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S. Zschaeck performed the analysis, drafted the manuscript, designed the figures, and calculated the underlying statistics. R. Graf, V. Budach, P. Wust, W. Wlodarczyk, M. Weihrauch, and R. Schild were responsible for treatment and treatment planning. M. Weihrauch provided technical support for the data evaluation. A.H. Thieme, P. Wust, and P. Ghadjar provided ideas and help with the manuscript. P. Wust and P. Ghadjar provided ideas for the analysis, supervised the analysis and data interpretation, and reviewed the manuscript. All authors read and approved the final manuscript.
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Zschaeck, S., Wust, P., Graf, R. et al. Spinal cord constraints in the era of high-precision radiotherapy. Strahlenther Onkol 193, 561–569 (2017). https://doi.org/10.1007/s00066-017-1138-5
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DOI: https://doi.org/10.1007/s00066-017-1138-5