Three-dimensional dose distribution for partial irradiation of rat parotid glands with 200kV X-rays.
OBJECTIVE
To investigate dose distributions in partial-volume irradiation experiments in small experimental animals, in particular the parotid gland of rat.


METHODS
High-resolution magnetic resonance imaging images were made that provided the outlines of the parotid glands, which were used to design collimators with conformal radiation ports for 100 and 50% cranial/caudal partial-volume irradiation. A protocol for absolute dosimetry was designed and relative dose measurements were performed. From the three-dimensional topographical data and the three-dimensional dose distribution, dose-volume histograms were determined.


RESULTS
The standard uncertainty of absorbed entrance dose was within 3%. Radiochromic film, thermoluminescence dosemeters and ionization chamber dose measurements revealed that the relative doses measured were in good agreement. The 20-80% penumbra of the beam across the 50% field edge was only 0.4 mm at a 6 mm depth. The gradient of the percentage depth dose from the skin of the rat to a depth of 12 mm was 1.5% mm(-1). The absorbed doses in the cranial 50% and the caudal 50% partial volumes were comparable. This finding was reflected in the calculated dose-volume histograms of the different regions, which were similar. The dose in the shielded area between the left and right ports was about 14% of the dose near the centres of the beams.


CONCLUSIONS
The designed set-up showed that irradiation of small volumes could be performed with high accuracy allowing the study of differences in radiation damage. Similar doses were given to the 50% cranial and 50% caudal gland volumes and, therefore, a possible difference in radiosensitivity in these volumes was not a dose effect. The approach used was also applicable for the irradiation of small volumes of other tissues.
Cotteleer
F
F
Department of Radiation and Stress Cellbiology, University of Groningen, Groningen, The Netherlands.
Faber
H
H
Konings
A W T
AW
Van der Hulst
P C
PC
Coppes
R P
RP
Meertens
H
H
D000818:Animals; D001822:Body Burden; D015331:Cohort Studies; D005240:Feasibility Studies; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D010306:Parotid Gland / Q000033:anatomy & histology* / Q000528:radiation effects; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011836:Radiation Tolerance; D011874:Radiometry / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D051381:Rats; D017208:Rats, Wistar; D013382:Subtraction Technique