Reirradiation human spinal cord tolerance for stereotactic body radiotherapy.
OBJECTIVE
We reviewed the treatment for patients with spine metastases who initially received conventional external beam radiation (EBRT) and were reirradiated with 1-5 fractions of stereotactic body radiotherapy (SBRT) who did or did not subsequently develop radiation myelopathy (RM).


METHODS
Spinal cord dose-volume histograms (DVHs) for 5 RM patients (5 spinal segments) and 14 no-RM patients (16 spine segments) were based on thecal sac contours at retreatment. Dose to a point within the thecal sac that receives the maximum dose (P(max)), and doses to 0.1-, 1.0-, and 2.0-cc volumes within the thecal sac were reviewed. The biologically effective doses (BED) using α/β = 2 Gy for late spinal cord toxicity were calculated and normalized to a 2-Gy equivalent dose (nBED = Gy(2/2)).


RESULTS
The initial conventional radiotherapy nBED ranged from ~30 to 50 Gy(2/2) (median ~40 Gy(2/2)). The SBRT reirradiation thecal sac mean P(max) nBED in the no-RM group was 20.0 Gy(2/2) (95% confidence interval [CI], 10.8-29.2), which was significantly lower than the corresponding 67.4 Gy(2/2) (95% CI, 51.0-83.9) in the RM group. The mean total P(max) nBED in the no-RM group was 62.3 Gy(2/2) (95% CI, 50.3-74.3), which was significantly lower than the corresponding 105.8 Gy(2/2) (95% CI, 84.3-127.4) in the RM group. The fraction of the total P(max) nBED accounted for by the SBRT P(max) nBED for the RM patients ranged from 0.54 to 0.78 and that for the no-RM patients ranged from 0.04 to 0.53.


CONCLUSIONS
SBRT given at least 5 months after conventional palliative radiotherapy with a reirradiation thecal sac P(max) nBED of 20-25 Gy(2/2) appears to be safe provided the total P(max) nBED does not exceed approximately 70 Gy(2/2), and the SBRT thecal sac P(max) nBED comprises no more than approximately 50% of the total nBED.
Department of Radiation Oncology, Sunnybrook Health Sciences Centre, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, Canada. Arjun.sahgal@rmp.uhn.on.ca
Arjun
A
Sahgal
Lijun
L
Ma
Vivian
V
Weinberg
Iris C
IC
Gibbs
Sam
S
Chao
Ung-Kyu
UK
Chang
Maria
M
Werner-Wasik
Liliyanna
L
Angelov
Eric L
EL
Chang
Moon-Jun
MJ
Sohn
Scott G
SG
Soltys
Daniel
D
Létourneau
Sam
S
Ryu
Peter C
PC
Gerszten
Jack
J
Fowler
C Shun
CS
Wong
David A
DA
Larson
D000293:Adolescent; D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000532:radiotherapy; D002292:Carcinoma, Renal Cell / Q000532:radiotherapy / Q000556:secondary / Q000601:surgery; D002817:Chordoma / Q000532:radiotherapy; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms; D008297:Male; D008875:Middle Aged; D011832:Radiation Injuries / Q000150:complications* / Q000175:diagnosis; D011836:Radiation Tolerance; D016634:Radiosurgery / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D012062:Relative Biological Effectiveness; D019233:Retreatment; D012189:Retrospective Studies; D013116:Spinal Cord / Q000528:radiation effects* / Q000601:surgery; D013118:Spinal Cord Diseases / Q000209:etiology; D013125:Spinal Neoplasms / Q000532:radiotherapy / Q000556:secondary* / Q000601:surgery*