Alpha/beta ratio for arteriovenous malformations estimated from obliteration rates after fractionated and single-dose irradiation.
OBJECTIVE
Results from single-dose radiosurgery have failed to yield reasonable alpha/beta ratios for obliteration rates of arteriovenous malformations (AVMs) in the framework of the linear-quadratic approach. We used outcome data from single-dose and fractionated radiotherapy for AVM to approach this problem.


METHODS
AVM obliteration rates observed in an updated historical series of fractionated radiotherapy and from six recent series of single-dose stereotactic radiosurgery were analyzed. Reciprocal total doses (1/D) and fraction sizes (d) of isoeffective fractionation schemes were entered into the rearranged form of the linear-quadratic equation: 1/D = (alpha/E) + (beta/E)d, and alpha/beta-ratios were calculated from the parameters of the regression line.


RESULTS
Fractionated radiotherapy with 20 Gy/4 Gy fractions, 50 Gy/2 Gy fractions and single-dose radiosurgery of approximately 13 Gy were isoeffective with crude obliteration rates of 13%. The analysis yielded an alpha/beta-ratio of 3.5 Gy. For small-sized AVMs (<3 cm), alpha/beta-ratios of 4.6-6.4 Gy were obtained.


CONCLUSIONS
These results support the view that radiosurgery for AVM can be understood as a typical late tissue effect with a high fractionation sensitivity. Fractionated radiotherapy is ineffective for AVMs and should be evaluated carefully in other benign targets.
Kocher
Martin
M
Department of Radiation Oncology, University of Cologne, Cologne, Germany.
Wilms
Marc
M
Makoski
Hans-Bruno
HB
Hassler
Werner
W
Maarouf
Mohammad
M
Treuer
Harald
H
Voges
Jürgen
J
Sturm
Volker
V
Müller
Rolf-Peter
RP
D019583:Dose Fractionation, Radiation; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000601:surgery*; D016634:Radiosurgery; D011879:Radiotherapy Dosage