Partial volume tolerance of the spinal cord and complications of single‐dose radiosurgery

Abstract

BACKGROUND.Spine radiosurgery causes a rapid dose fall‐off within the spinal cord. The tolerance of partial volume of the spinal cord may determine the extent of clinical application. The study analyzed the partial volume tolerance of the human spinal cord to single fraction radiosurgery.METHODS.A total of 230 lesions with spine metastases in 177 patients were treated with radiosurgery with single fraction of 8 to 18 Gy, prescribed to the 90% isodose line that encompassed the target volume. Spinal cord volume was defined as 6 mm above and below the radiosurgery target volume. Spinal cord dose was calculated from the radiation dose/spinal cord volume histogram and correlated with clinical/neurological status and radiographic studies. Median follow‐up was 6.4 months (range, 0.5–49 months). The 1‐year survival rate was 49%.RESULTS.The average spinal cord volume defined at the treated spinal segment was 5.9 ± 2.2 mL. The average dose to the 10% spinal cord volume was 9.8 ± 1.5 Gy, calculated from the dose‐volume histogram in the group of 18 Gy prescribed dose. The spinal cord volume that received higher than 80% of the prescribed dose was 0.07 ± 0.10 mL, which represented 1.3 ± 1.8% of the cord volume. Among the 86 patients who survived longer than 1 year there was 1 case of radiation‐induced cord injury after 13 months of radiosurgery. There were no other cases of spinal cord sequelae.CONCLUSIONS.Whereas the maximum spinal cord tolerance to single‐dose radiation is not known, partial volume tolerance of the human spinal cord is at least 10 Gy to 10% of the spinal cord volume defined as 6 mm above and below the radiosurgery target. Cancer 2007;109:628–636. © 2006 American Cancer Society.

Submillimeter alignment of more than three contiguous vertebrae in spinal SRS/SBRT with 6‐degree couch

“…The risks of radiation myelopathy in spinal SRS/SBRT were very well studied6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 with Dmax been generally accepted as the parameter of dosimetric constraint. Kirkpatrick et al summarized nine published reports of spinal cord dose and myelopathy in 1,400 patients who received spinal SRS/SBRT 16.…”

Intensity‐modulated radiotherapy versus proton radiotherapy versus carbon ion radiotherapy for spinal bone metastases: a treatment planning study

“…The spinal cord was delineated on a planning CT scan after fusion with an MRI or CT myelography. The partial spinal cord and partial spinal cord PRV was limited to 6 mm above and below the PTV (19) . Depending on the location of the vertebrae and the PTV, other organs at risk (OAR) that were segmented included liver, lungs, esophagus, bowel, skin, large vessels, and kidneys.…”

Spinal metastases: From conventional fractionated radiotherapy to single-dose SBRT

“…39 The median total radiation dose was 24 Gy (range, 18-35 Gy), in a mean of 3 fractions (range, 1-5). With a median follow-up for the cohort of 13 months (range, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], local control based on imaging was achieved in 7 of the 10 patients treated.…”

“…Other studies have suggested that the spinal cord can tolerate at least a single dose of 10 Gy to 10% of the cord segment that is adjacent to a targeted tumor plus 6 mm above and below this segment, with a risk of radiation-induced myelopathy of <0.5%. 16 Sahgal et al reported Dose-Volume Histograms (DVH) of nine patients who developed radiation myelopathy post-SBRT and compared them with a cohort of 66 spine SBRT patients who did not develop the toxicity. 17 A logistic regression model was developed to establish the probability of myelopathy using the thecal sac point maximum (Pmax) volume.…”