Bath and Shower Effects in the Rat Parotid Gland Explain Increased Relative Risk of Parotid Gland Dysfunction After Intensity-Modulated Radiotherapy
Received 5 March 2009; received in revised form 13 March 2009; accepted 15 March 2009.
Purpose
To assess in a rat model whether adding a subtolerance dose in a region adjacent to a high-dose irradiated subvolume of the parotid gland influences its response (bath-and-shower effect).
Methods and Materials
Irradiation of the whole, cranial 50%, and/or the caudal 50% of the parotid glands of Wistar rats was performed using 150-MeV protons. To determine suitable (i.e., subtolerance) dose levels for a bath-dose, both whole parotid glands were irradiated with 5 to 25 Gy. Subsequently groups of Wistar rats received 30 Gy to the caudal 50% (shower) and 0 to 10 Gy to the cranial 50% (bath) of both parotid glands. Stimulated saliva flow rate (function) was measured before and up to 240 days after irradiation.
Results
Irradiation of both glands up to a dose of 10 Gy did not result in late loss of function and is thus regarded subtolerance. Addition of a dose bath of 1 to 10 Gy to a high-dose in the caudal 50% of the glands resulted in enhanced function loss.
Conclusion
Similar to the spinal cord, the parotid gland demonstrates a bath and shower effect, which may explain the less-than-expected sparing of function after IMRT.
∗Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
†Accelerator Department, Paul Scherrer Institut, Villigen, Switzerland
‡Kernfysisch Versneller Instituut, University of Groningen, Groningen, the Netherlands
§Department of Cell Biology, Section Radiation and Stress Cell Biology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
Reprint requests to: Peter van Luijk, Ph.D., P.O. Box 30001, 9700 RB, Groningen, The Netherlands. Tel: +31-50-3611739; Fax: +31-50-3611692
ABSTRACT