Abstract:
This research has been prepared at radiation and Isotopes center- Khartoum
(RICK) in order to measure the entrance and exit dose in radiotherapy using films
compose of Poly Vinyl Alcohol grafted with Silver Nitrate.
The PVA solutions were made by dissolving PVA in distilled water at temperature of 80
o
C on a beaker. The solution was magnetically stirred throughout at that temperature for
3 hours, After cooling to room temperature, we took the PVA solution into dark room
and hybridized with silver nitrate and stirred for 2h. Then the PVA /AgNo3 solution
spread into a specially made glass caster, 10 cm in diameter and left to dry at ambient
temperature in dark room for at least 3 days to remove water. Then films will be peeled
off the glass caster and cut into small films 2x2cm, and loaded in sealed dark plastic
packs (dental film envelope).
Then the films together with TLD were irradiated with γ-ray from Co60 radiotherapy
machine and receiving doses in the range of 1, 2, 4... 12 and 15 Gy) at entrance and exit
beam of a solid phantom in a build up region (0.5 cm).
The result showed a color changes from white to light yellow, golden, brown and dark
brown according to the dose that received to each film. The characterization of films by
UV-visible spectroscope showed an absorption peaks at 200 and 410 nm, and the
absorption peak increase following the increment of applied radiation dose in a linear
form based on the following equations: y = 0.993x +0.6624, y = 0.111x + 0.1024, for
entrance and exit doserespectively, where y refers to the absorption in (au) and x refers to
the dose in Gray (Gy) with a correlation coefficient of R2 = 0.99. And the optical density
showed great and significant relation with the applied dose in a form of linear
proportional relation based on the following equations:
y =0.0404x + 0.1171, y =0.0312x + 0.0996 for both entrance and exit doses
respectively, where y refers to optical density and x refers to the applied dose in Gy with
a correlation coefficient of R2 = 0.98.
Also the PVA/AgNo3 composite films were exposed together with TLD in Co60
radiotherapy machine using field size 10x10 SSD 100cm.The results of optical density
and UV visible spectroscopy analysis indicated that there are a good compatible with the
TLD result.
