Radiation tolerance of the rat spinal cord after 6 and 18 fractions of photons and carbon ions: Experimental results and clinical implications
- Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg (Germany)
- Department of Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg (Germany)
- Department of Central Animal Laboratory, German Cancer Research Center (DKFZ), Heidelberg (Germany)
- Department of Biophysics, Gesellschaft fuer Schwerionenforschung (GSI), Darmstadt (Germany)
- Department of Clinical Radiology, University of Heidelberg, Heidelberg (Germany)
Purpose: The tolerance of the rat spinal cord to photon and carbon ion irradiations was investigated to determine the relative biologic effectiveness (RBE) of carbon ions ({sup 12}C) in the plateau region and in a 1 cm spread-out Bragg-peak. Methods and Materials: The cranial part of the cervical and thoracic spinal cord of 336 rats was irradiated with 6 or 18 fractions (Fx) of photons or {sup 12}C-ions, respectively. Animals were followed up for 300 days for the onset of paresis grade II and dose-response curves were calculated. Results: The D{sub 5}-values (dose at 50% complication probability) were 42.9 {+-} 0.5 Gy, 62.2 {+-} 0.9 Gy (6 and 18 Fx, {sup 12}C-plateau) and 19.2 {+-} 0.2 Gy, 17.6 {+-} 0.2 Gy (6 and 18 Fx {sup 12}C-peak), respectively. For photons, the D{sub 5}-values were 57.0 {+-} 0.7 Gy for 6 and 88.6 {+-} 0.7 Gy for 18 Fx. The corresponding RBE-values were 1.33 {+-} 0.02, 1.42 {+-} 0.02 (6 and 18 Fx, {sup 12}C-plateau) and 2.97 {+-} 0.05, 5.04 {+-} 0.08 (6 and 18 Fx {sup 12}C-peak), respectively. Including data of a previously performed experiment for 1 and 2 Fx () the parameter {alpha}/{beta} of the LQ-model was found to be 2.8 {+-} 0.4 Gy, 2.1 {+-} 0.4 Gy and 37.0 {+-} 5.3 Gy for photon-, {sup 12}C-plateau- and {sup 12}C-peak irradiations, respectively. Conclusions: Carbon ion irradiations of the spinal cord are significantly more effective in the peak than in the plateau region. The {alpha}/{beta}-values indicate a significant fractionation effect only for the plateau irradiations. In the Bragg-peak, the applied RBE-model correctly describes the main features although it generally underestimates the RBE by 25%. In the plateau region, maximum deviations of up to 20% were found. The acquired data contribute significantly to the validation of the applied RBE-model.
- OSTI ID:
- 20850275
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 66, Issue 5; Other Information: DOI: 10.1016/j.ijrobp.2006.08.045; PII: S0360-3016(06)02808-2; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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