Page 60 - PR 2014 2016 07 Nuclear Science and Technology

202 Nuclear Science and Technology | Progress Report

projected and developed a Fricke Xylenol Gel due to the curvature of the patient’s body, the
phantom capable of measuring the differences angles of electron incidence that are varied and
introduced by movement using the Magnetic the orientation of the bundles. In this study,
Resonance Image - MRI and compared qualita- LiF:Mg,Ti and CaSO :Dy dosimeters were used
4
tively and quantitatively with other systems. to evaluate the entrance dose distribution to
The congruence of the isodose curves, with the the skin. The LiF:Mg,Ti showed uncertainty
signal intensity of the MRI image and the large of ± 0,1% and CaSO :Dy, ± 0,2%. In the TSI irra-
4
difference in signal intensity of the MRI image diation procedure, the real conditions for the
with the isodoses, shows that the movement patient’s treatment were implemented. An
generates a blurring are shown in figure 37. anthropomorphic phantom (Figure 38) was po-
sitioned on a turntable and the TL dosimeters
were positioned in several anatomical regions
such as abdomen, thorax center, thorax right,
thorax left, posterior, right side, right thigh,
perineum and front. The doses were acquired
on alternate days, allowing a better study of
the skin. Other factors were analyzed in this
study, such as the homogeneity of the field
and the dose at the calibration point (ZRef).
Considering the characteristics of the irra-
Figure 37- Fricke Gel Phantom VMAT Irradiation and con- diation field, the maximum dose deposition
gruence between dose distribution and MRI signal.
should be delivered in a few millimeters of
the skin surface (5 - 15 mm). Comparing the
Comparative study of the TL response in dose at the calibration point, a small variation
clinical electron beams dosimetry applied to was observed in relation to the other points
Total Skin Irradiation – TSI Treatments studied such as the posterior region and the
right side of the anthropomorphic phantom.
Total Skin Irradiation - TSI is a radiotherapy The TL dosimeters presented good results for
technique applied in the treatment of certain dose evaluation in TSI treatment.
generalized malignant diseases of the skin.
This treatment aims to irradiate the patient’s
entire skin evenly with large electron fields. Figure 38
The radiation penetrates a few millimeters - Phantom
AldersonRando®
into the skin and reaches the affected part used in clinical
completely without penetrating the internal electron beams
dosimetry applied
organs. The application of electrons in therapy to Total Skin
requires great accuracy in the dose absorbed Irradiation – TSI
Treatments.
by the tumor since a variation of ± 5% is deter-
minant in the risk of relapse or sequelae. In the
TSI Stanford technique, the patient is treated
by a two-day cycle with three dual fields per
day. When the patient is placed in the six po-
sitions with a double field irradiation at each
position, the dose is considered less uniform

Instituto de Pesquisas Energéticas e Nucleares