The dose tolerance related to brainstem toxicity in radiosurgery

Jinyu Xue1, Jimm Grimm2, Lesley Hughes2, Yan Chen2, Tamara LaCouture2, Warren Goldman3

1Camden, United States 2Department of Radiation Oncology, Cooper University Hospital 3Neurological Institute, Cooper University Hospital

Keywords: gamma knife, trigeminal neuralgia, radiation injury, complications, radiosurgery

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     Brainstem radiation dose tolerance is an important concept to study.
This work presents a set of new data for better understanding of brainstem dose-volume tolerance limits applicable to stereotactic radiosurgery (SRS). The QUANTEC report, based on very limited data, cited a maximum dose of 12.5 Gy for less than 5% serious complications.
     30 patients were studied.
     We performed a retrospective analysis of 30 trigeminal neuralgia (TN) cases treated with Gamma Knife Perfexion at Cooper University Hospital between September 2007 and January 2011. Our prescription dose had a maximum of 80 ~ 85 Gy with the 50% isodose line touching brainstem. Two of our patients (6%) had mild facial numbness. No unexpected radiologic changes were seen in the post-op MRI for any of our patients. The mean time of our patient follow-up was 25 months (ranges: 4 to 39 months) after the GK procedure.
     Based on the dose volume histogram (DVH) data of our TN cases (1mm voxel size resolution), the mean values and standard deviations of brainstem dosimetric data are as follows: 44.5 Gy (±1.6) to a volume of 0.1 mm3 (i.e., Dmax), 37.9 Gy (±1.4) to a volume of 1 mm3, 18.4 Gy (±0.4) to a volume of 0.03 cc, 11.0 Gy (±0.3) to a volume of 0.1 cc, 3.3 Gy (±0.2) to a volume of 1 cc and 9.9 Gy (±0.6) to 1% volume of brainstem. Maximum doses of either 44.5 Gy or 37.9 Gy are well beyond the QUANTEC range of acceptable dose tolerances in a single fraction.
     TN patients treated with radiosurgery are a valuable population for the study of dose-volume effects on brainstem complications at extreme hypofractionation. GKRS treatments are believed to have an average clinical accuracy within less than a millimeter. Therefore, the dose distribution delivered to the brainstem in GKRS is probably very close to that planned. TN radiosurgery results suggest that a very small volume of brainstem can tolerate drastically high dose without causing any clinically severe injury. 
     Our analysis demonstrates that radiation related brainstem toxicity in SRS for TN has a novel type of dose-volume effect and that closer analysis of data from this patient group may lead to unique and interesting insights.


Project Roles:

J. Xue (), J. Grimm (), L. Hughes (), Y. Chen (), T. LaCouture (), W. Goldman ()