Influence of adjacent low-dose fields on tolerance to high doses of protons in rat cervical spinal cord

HP Bijl*, P van Luijk, RP Coppes, JM Schippers, AWT Konings, AJ van der Kogel

*Bijbehorende auteur voor dit werk

OnderzoeksoutputAcademicpeer review

41 Citaten (Scopus)

Samenvatting

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 ED50 values of 61.2 Gy and 68.6 Gy for the symmetrical and asymmetrical arrangement, respectively, compared with an ED50 of 87.8 Gy after irradiation of a 2-mm field only. If the bath dose is increased to 18 Gy, the ED50 value is decreased further to 30.9 Gy. For an 8-mm field, addition of a 4-Gy bath dose did not modify the ED50 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. (C) 2006 Elsevier Inc.

Originele taal-2English
Pagina's (van-tot)1204-1210
Aantal pagina's7
TijdschriftInternational Journal of Radiation Oncology Biology Physics
Volume64
Nummer van het tijdschrift4
DOI's
StatusPublished - 15-mrt-2006

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