Probabilities of radiation myelopathy specific to stereotactic body radiation therapy to guide safe practice.
OBJECTIVE
Dose-volume histogram (DVH) results for 9 cases of post spine stereotactic body radiation therapy (SBRT) radiation myelopathy (RM) are reported and compared with a cohort of 66 spine SBRT patients without RM.


METHODS
DVH data were centrally analyzed according to the thecal sac point maximum (Pmax) volume, 0.1- to 1-cc volumes in increments of 0.1 cc, and to the 2 cc volume. 2-Gy biologically equivalent doses (nBED) were calculated using an α/β = 2 Gy (units = Gy(2/2)). For the 2 cohorts, the nBED means and distributions were compared using the t test and Mann-Whitney test, respectively. Significance (P<.05) was defined as concordance of both tests at each specified volume. A logistic regression model was developed to estimate the probability of RM using the dose distribution for a given volume.


RESULTS
Significant differences in both the means and distributions at the Pmax and up to the 0.8-cc volume were observed. Concordant significance was greatest for the Pmax volume. At the Pmax volume the fit of the logistic regression model, summarized by the area under the curve, was 0.87. A risk of RM of 5% or less was observed when limiting the thecal sac Pmax volume doses to 12.4 Gy in a single fraction, 17.0 Gy in 2 fractions, 20.3 Gy in 3 fractions, 23.0 Gy in 4 fractions, and 25.3 Gy in 5 fractions.


CONCLUSIONS
We report the first logistic regression model yielding estimates for the probability of human RM specific to SBRT.
Department of Radiation Oncology, Princess Margaret Hospital, University of Toronto, Toronto, ON, Canada. arjun.sahgal@rmp.uhn.on.ca
Arjun
A
Sahgal
Vivian
V
Weinberg
Lijun
L
Ma
Eric
E
Chang
Sam
S
Chao
Alexander
A
Muacevic
Alessandra
A
Gorgulho
Scott
S
Soltys
Peter C
PC
Gerszten
Sam
S
Ryu
Lilyana
L
Angelov
Iris
I
Gibbs
C Shun
CS
Wong
David A
DA
Larson
D019540:Area Under Curve; D016022:Case-Control Studies; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects*; D011336:Probability; D011832:Radiation Injuries / Q000209:etiology*; D016634:Radiosurgery / Q000009:adverse effects* / Q000379:methods / Q000706:statistics & numerical data; D013116:Spinal Cord / Q000528:radiation effects*; D013125:Spinal Neoplasms / Q000556:secondary / Q000601:surgery*; D018709:Statistics, Nonparametric