2005 International Nuclear Atlantic Conference - INAC 2005
Santos, SP, Brazil, August 28 to September 2, 2005
ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN
ISBN: 85-99141-01-5
THE FRICKE XYLENOL GEL (FXG) DOSIMETRY IN THE MYCOSIS
FUNGOIDES RADIOTHERAPY
Herofen Zaias1, Paulo C.D. Petchevist1, Marco A. Parada1, Adelaide de Almeida1,
Alessandro M. da Costa1 and José Renato de Oliveira Rocha2
1
Departamento de Física e Matemática
Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto
Universidade de São Paulo
Av. Bandeirantes, 3900
CEP 14040-901, Ribeirão Preto, SP, Brazil
[email protected]
2
Centro de Engenharia Biomédica
Universidade Estadual de Campinas
Caixa Postal 6040
CEP 13084-971, Campinas, SP, Brazil
[email protected]
ABSTRACT
We used chemical dosimetry with the Fricke Xylenol Gel (FXG) dosimeter to verify the dose distribution in an
electron therapy of mycosis fungoides. Anatomically shaped phantoms were developed and filled with the FXG.
The phantons were inserted in a “Rando” antropomorphic phantom and submitted to the Stanford irradiation
technique with a 6MeV electron beam. The absorbances of the FXG after the irradiation were measured with a
special FXG reader developed for this purpose. The preliminary results show that the FXG dosimetry system is
a promising dosimetry technique.
1. INTRODUCTION
Whole-body electron therapy can be used for widespread infiltrative lesions of skin primary
limphoma (mycosis fungoides). Mycosis fungoides treatment through the Stanford technique
consists of irradiating the patient with two electron beams tilted 20º above and 20º below of a
horizontal axis in the patient waistline. The patient is placed standing up and perpendicular to
the beam on a rotative base, distant 3 m from the source. The patient is equally exposed in
each of six angular positions at 60º intervals, approximating uniform angular irradiation. In
order to spread and attenuate the incident beam a polymethylmethacrylate (PMMA) plate
(200 cm × 100 cm × 1 cm) is placed in front of the patient [1].
Usually a treatment simulation, using a “Rando” antropomorphic phantom (70 kg of weight
and 1,70 m of height), is done with a film placed between two slices of the skull and waistline
in order to verify the dose distribution. In this work the dose distribution was verifyed with an
alternative method which is under study and which could present its own advantages in the
future. This method is the FXG chemical dosimetry [2–5].
2. MATERIALS AND METHODS
The irradiations were carried out using a 6 MeV electron beam from a linear accelerator
Siemens/Mevatron 74.
The dose distribution was verifyed using a “Rando” antropomorphic phantom. Two specific
slices (one in the skull and other in the waistline) to be used in the humanoid phantom were
developed and filled with the FXG gel. The slice walls were made of 1mm thick PMMA and
an illustration of these phantoms are shown in the Fig. 1.
(a) Waistline
(b) Skull
Figure 1. Humanoid phantom slices. The white
circles are support rods to maintain the slices
structures.
The slices developed were inserted in the “Rando” (Fig. 2) and submitted to the Stanford
irradiation technique with the 6 MeV electron beam.
The FXG irradiation oxidizes Fe2+ into Fe3+ and the ferric ion concentration can be
determined using spectrophotometry to measure the FXG absorbance.
Once irradiated, the slices were submitted to absorbance measurements with a FXG reader,
developed with a high brightness LED source, a photodiode for signal detection, a light
emission and reception circuit and a voltmeter connected to the receptor circuit to register the
luminous signal intensity variation. Fig. 3 shows the FXG reader.
INAC 2005, Santos, SP, Brazil.
Figure 2. Humanoid phantom with the two
developed slices.
Figure 3. FXG slice reader composed by an “arm”
which houses the LED in good alignment with the
photodiode in the reader base.
3. RESULTS AND DISCUSSION
Fig. 4 shows the percentage depth dose (PDD) versus depth for each slice. These absorbance
results from the quasi-bidimensional slices, inserted in the “Rando” antropomorphic
phantom, show satisfactory dose distributions as expected from film measurements [6].
From the entry point the absorbed dose drops off rapidly and tends to level off at a small
value referred as the bremsstrahlung tail.
INAC 2005, Santos, SP, Brazil.
Figure 4. PDD for 6 MeV electron beam
irradiation of the phantom versus distance from
the edge slice surface.
4. CONCLUSIONS
Our preliminary results show that chemical dosimetry with the FXG is a promising relative
dosimetry technique which may prove particularly useful for dose verification in
anatomically shaped phantoms.
ACKNOWLEDGMENTS
The authors would like to thank the financial support from Coordenação de Aperfeiçoamento
de Pessoal de Nível Superior (CAPES), Brazil.
REFERENCES
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measurements with ferrous benzoic acid xylenol orange in gelatin gel and optical
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(1999).
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INAC 2005, Santos, SP, Brazil.
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INAC 2005, Santos, SP, Brazil.