Bath and shower effects in the rat parotid gland explain increased relative risk of parotid gland dysfunction after intensity-modulated radiotherapy.
OBJECTIVE
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
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.


CONCLUSIONS
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.
van Luijk
Peter
P
Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands. p.van.luijk@rt.umcg.nl
Faber
Hette
H
Schippers
Jacobus M
JM
Brandenburg
Sytze
S
Langendijk
Johannes A
JA
Meertens
Harm
H
Coppes
Robert P
RP
D000818:Animals; D008297:Male; D010306:Parotid Gland / Q000502:physiology / Q000528:radiation effects*; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control; D011836:Radiation Tolerance / Q000502:physiology*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D051381:Rats; D017208:Rats, Wistar; D012472:Salivation / Q000528:radiation effects*; D014987:Xerostomia / Q000209:etiology*