Functional assessment of spinal cord injury following irradiation

Proceedings

of the 31st Annual

163

ASTRO Meeting

93 FUNCTIONAL

ASSESSMENT

OF SPINAL

E.R. Beck,

R.A. LeCouteur,*

CORD INJURY

E.L. Gillette,

Depts of Radiology&Radiation

Biology

FOLLOWING

IRRADIATION

G. Childs*

and *Clinical

Colorado

Sciences,

State University,

Fort Collins,

CO

80523

Radiation myelopathy continues to be one of the most devastating late complications of radiation therapy. cord. the injury to spinal radiation evaluate subclinical No method currently exists which can Electrophysiologic measurements which correlated with the development of clinical myelopathies could be potentially useful in monitoring spinal cord function in patients considered at risk for the development of radiation myelopathyby predicting late effects from early changes. Residual damage determined by the conduction Tissue injury velocities of previously treated asymptomatic patients could be used as a guide in retreatment. could be followed sequentially if the endpoint did not perturb the tissue being evaluated and if the endpoint closely correlated with the clinical syndrome of radiation myelopathy in man. The thoracic spinal cord of 57 adult beagle dogs was irradiated using 4 Gy fractions to total doses of 44, first by complete An animal's response to irradiation was evaluated by 2 methods: 52, 60, 68 and 76 Gy. and secondly by measurement of the speed with which the spinal cord was able to neurological examinations, were used to calculate the Evoked spinal cord potentials or the conduction velocity. conduct impulses, A steep dose response conduction velocity through specific areas of irradiated and unirradiated spinal cord. The median tolerance dose (EDso) for permanent neurologic was seen for the development of radiation myelopathy. When an equivalent dose using 2 Gy fractions was injury was 56.4 Gy in 4 Gy fractions with a SE of 1.9 Gy. calculated, the dose to produce 50% paralysis was 79.0 Gy, which was quite similar to values found for 50% paralysis in the monkey and rat (70 to 79.9 Gy) or to values calculated for the human spinal cord (74 to 84 Gy). The conduction velocity of irradiated spinal cords decreased as early as 2 weeks following the 4 week Five course of irradiation, but several weeks to months prior to the onset of clinical signs in all animals. of 8 animals receiving 60 Gy, 2 of 7 animals receiving 52 Gy, and all animals receiving 76 and 60 Gy developed Other animals receiving 60 and 52 Gy, radiation myelopathy. All had conduction velocities less than 60 m/s. The All had conduction velocities greater than 65 m/s. and all animals receiving 44 Gy were asymptomatic. minimum conduction velocity was strongly associated with the development and severity of myelopathy (p < 0.001) as early as 12 weeks in some animals, but by 9 months following irradiation in all animals. This investigation was supported by PHS grant numbers CA13899 and CA09236, awarded by the National Cancer Institute, DHHS.

94 THERISKOFRADIATIONMYELITISOFTHECERVICALSPINALCORDINTHETREATMENTOFHEADANDNECK CANCER

Robert B. Marcus, Jr.,

M.D., Rodney R. Million,M.D.

Dept. of Radiation Oncology,

Radiation further

define

myelitis

receive

radiation

of Florida

is one of the most feared

the tolerance

2,934 head and neck cancer included

University

of the cervical patients

College

complications

Gainesville,

in the practice

spinal cord, the dose of radiation

seen at our insititution

between

Florida.

of radiation to the cervical

lo/64 and 12/W.

if they received treatment,

for anlaysis.

a dose greater unless myelitits

patients

were eligible

cervical

cord at 173 cGy per day, and the other patient at standard

above 4500 cGy, the risk appears

myelitis

fractionations

to be higher,

Dose to the Cervical

Spine

In an attempt

spine was calculated

Therefore,

patients

to

for all

either

did not

were only

than 3,000 cGy at 150-240 cGy per day to the spinal cord and occurred

Only two of these patients

table shows the risk of radiation

that the risk of myelitis

oncology.

Many of these patients

to the spinal cord or did not live long enough to be at risk for myelitis.

in the final analysis

lived for at least one year after

following

of Medicine,

prior to one year.

developed

received

radiation

Using these conditions,

myelitis.

4907 cGy to the cervical

One received

cord at 170 cGy per day.

for each dose range from 3000 cGy to 6000 cGy. is extremely

low for patients

receiving

The data clearly

less than 4500 cGy.

but it is still much less than 1%. No. Pts. at Risk

No. Pts. Developing

3000-4000 cGy

156

0

4001-4500 cGy

514

0

4501-5000 cGy

570

5001-6000 cGy

80

2 (0.35%) 0

1,320

4658 cGy to the

Myelitis

The show

For doses