Influence of adjacent low-dose fields on tolerance to high doses of protons in rat cervical spinal cord
- Department of Radiation Oncology, University of Groningen and University Medical Center Groningen, Groningen (Netherlands)
- Netherlands
- Kernfysisch Versneller Instituut, Groningen (Netherlands)
- Department of Radiation and Stress Cell Biology, University of Groningen and University Medical Center Groningen, Groningen (Netherlands)
- Department of Radiation Oncology, University Medical Center Nijmegen, Nijmegen (Netherlands)
Purpose: The dose-response relationship for a relatively short length (4 mm) of rat spinal cord has been shown to be significantly modified by adjacent low-dose fields. In an additional series of experiments, we have now established the dose-volume dependence of this effect. Methods and Materials: Wistar rats were irradiated on the cervical spinal cord with single doses of unmodulated protons (150 MeV) to obtain sharp lateral penumbras, by use of the shoot-through technique, which employs the plateau of the depth-dose profile rather than the Bragg peak. Three types of inhomogeneous dose distributions were administered: Twenty millimeters of cervical spinal cord were irradiated with variable subthreshold (= bath) doses (4 and 18 Gy). At the center of the 20-mm segment, a short segment of 2 mm or 8 mm (= shower) was irradiated with variable single doses. These inhomogeneous dose distributions are referred to as symmetrical bath-and-shower experiments. An asymmetrical dose distribution was arranged by irradiation of 12 mm (= bath) of spinal cord with a dose of 4 Gy. The caudal 2 mm (= shower) of the 12-mm bath was additionally irradiated with variable single doses. This arrangement of inhomogeneous dose distribution is referred to as asymmetrical bath-and-shower experiment. The endpoint for estimation of the dose-response relationships was paralysis of the fore limbs or hind limbs and confirmation by histology. Results: The 2-mm bath-and-shower experiments with a 4-Gy bath dose showed a large shift of the dose-response curves compared with the 2-mm single field, which give lower ED{sub 5} values of 61.2 Gy and 68.6 Gy for the symmetrical and asymmetrical arrangement, respectively, compared with an ED{sub 5} of 87.8 Gy after irradiation of a 2-mm field only. If the bath dose is increased to 18 Gy, the ED{sub 5} value is decreased further to 30.9 Gy. For an 8-mm field, addition of a 4-Gy bath dose did not modify the ED{sub 5} obtained for an 8-mm field only (23.2 and 23.1 Gy). Conclusions: The spinal cord tolerance of relatively small volumes (shower) is strongly affected by low-dose irradiation (= bath) of adjacent tissue. The results of all bath-and-shower experiments show the effect of a low bath dose to be highest for a field of 2 mm, less for 4 mm, and absent for 8 mm. Adding a 4-Gy bath to only 1 side of a 2-mm field still showed a large effect. Because glial progenitor cells are known to migrate over at least 2 to 3 mm, this observation indicates that interference with stem cell migration is not the most likely mechanism of a bath effect.
- OSTI ID:
- 20793402
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 64, Issue 4; Other Information: DOI: 10.1016/j.ijrobp.2005.06.046; PII: S0360-3016(05)02828-2; 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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