Cauda equina tolerance to high-dose fractionated irradiation.
OBJECTIVE
To report late neurologic toxicity rates and clinical outcomes for patients treated with high dose fractionated radiation therapy using three-dimensional treatment planning and combined proton and photon beams to portions of the cauda equina (L2-coccyx).


METHODS
Medical records of 53 patients treated to fields encompassing the cauda equina were reviewed for the onset of neurologic symptoms in the absence of local failure. All doses were normalized to equivalent dose delivered in 2-Gy fractions. Median cauda dose was 65.8 cobalt Gray equivalents (CGE) (range, 31.9-85.1). Median follow-up was 87 months (range, 14-217 months).


RESULTS
Nineteen patients experienced local recurrences, and 13 others had neurologic toxicity. A total of 54% (i.e., 7/13) of the toxicities occurred 5 years or more after treatment. Median caudal dose was 73.7 CGE in the group with neurologic toxicity, and 55.6 CGE in those without. On multivariate actuarial analysis, cauda dose and gender were statistically significant for neurotoxicity at p = 0.002 and p = 0.017, respectively. The estimated tolerance doses 5 years from treatment, TD 5/5 and TD 50/5, were 55 CGE and 72 CGE, respectively, for males and 67 CGE and 84 CGE for females. The tolerance doses were about 8 CGE lower when estimated at 10 years from treatment. Disease-free survival rates at 5 and 10 years were 66% and 53%, respectively.


CONCLUSIONS
This study suggests that the probability of neurotoxicity is a relatively steep function of dose to cauda equina (slope gamma50 = approximately 3). The cauda equina tolerance is greater for females than males by about 11 CGE (at 2 CGE per fraction). Extended follow-up is necessary to accurately assess neurologic damage and then differentiate that phenomenon from local recurrence; the traditional 5-year assessment has limited meaning in this population. Local control remains an issue for these patients, even with the radical doses used.
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
Richard S
RS
Pieters
Andrzej
A
Niemierko
Barbara C
BC
Fullerton
John E
JE
Munzenrider
D000206:Actuarial Analysis; D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D002420:Cauda Equina / Q000528:radiation effects*; D002648:Child; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017785:Photons / Q000627:therapeutic use; D061766:Proton Therapy; D011836:Radiation Tolerance / Q000502:physiology*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D012186:Retroperitoneal Neoplasms / Q000401:mortality / Q000532:radiotherapy; D012189:Retrospective Studies; D013125:Spinal Neoplasms / Q000401:mortality / Q000532:radiotherapy; D015996:Survival Rate; D011522:Protons
D011522:Protons