H. Tolli et Ka. Johansson, QUALITY ASSURANCE IN BRACHYTHERAPY - THE DISPLACEMENT EFFECT IN THE VICINITY OF CO-60 AND IR-192 BRACHYTHERAPY SOURCES, Physics in medicine and biology, 38(10), 1993, pp. 1485-1492
Cylindrical ionization chambers with varying radii have been used to d
etermine the displacement effect at distances between 10 mm and 40 mm
from Co-60 and Ir-192 brachytherapy sources. Agreement with published
values of the displacement factor for external Co-60 beams is obtained
. The shift between the centre of the ionization chamber and the effec
tive point of measurement is found to be only a few per cent of the in
ternal radius of the cylindrical ionization chamber. The shift is foun
d to be dependent on the source to ionization chamber centre distance.