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Determination of total uncertainty in dose of the radiochromic film dosimetry method

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Determination of total uncertainty in dose of the radiochromic film dosimetry method

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Samenvatting

The treatment of tumours in cancer patients have become more advanced and thus more
complex. The verification of the dose distribution, calculated by clinical physicists, have thus
become more complicated. VSL has started the development on measurements of absolute
dose distributions in an antrhopomorphic phantom. One of those developments at VSL is
the use of radio chromic dosimetry films (RCFD) to determine a dose distribution in two
dimensions. Irradiating films with the double irradiation technique in an anthropomorphic
phantom (PMMA) will be used to determine dose distributions that are traceable to primary
standard at VSL, the watercalorimeter. Films are read out with a flatbed scanner. The
scanning of the film introduces additional uncertainties to the dose determination procedure.
The delivered dose on the _lm in the water phantom is different than the delivered dose in
the PMMA phantom. Therefore a conversion factor between these two phantoms is needed
and will be investigated in this report. The uncertainties of the scan procedure will also be
investigated.

The conversion factor for the delivered dose to _lm in the PMMA and water phantom for
RCFD has been validated by irradiating films in the water phantom and in the PMMA
phantom. The ratio of OD ratios, RPMMA=Rwater, and its uncertainty of these delivered
doses has been determined. The calculated reference value of RPMMA=Rwater is compared
with the measured value. The effect of water can have an influence on the active layer of
the film, this effect has been investigated and measured. The influence of pre-irradiation
dose on film and its uncertainty has been investigated and determined. Experiments that
determine the uncertainties of the scanning procedure have been investigated and determined
for different components. Due to polarized films and scanner light, an additional source of
uncertainty, the polarization effect has also been investigated and determined. As a result of
all the measured uncertainties in the whole process of determining the dose distribution with
RCF, an uncertainty budget of both the irradiation of films process and the scanning has
been partially determined.

The difference between the measured value of the measured and the reference value of
RPMMA=Rwater is -0.4%. The measured and calculated reference value differ too much when
looked at the relative standard deviation of the measured value (0.0007). This value is used as
an additional uncertainty. The water influence on film is nonexistant, the determined values
of the ratio of the optical density between the control group of films and the in water dipped
films fall within each other’s standard devition. When films are pre-irradiated with 0.5 Gy,
it has been determined that the relative standard deviation on mean of R is greater than
when films are pre-irradiated with 1.0 Gy. The total uncertainty of scanning films has been
determined on a relative standard deviation of 0.007. Some physical quantities that can play
a role on the process of determining a dose distribution with RCF are yet to be determined.
Some physical quantities and its uncertainty of the whole process of determining the dose
distribution with RCF are yet to be determined, only when all of the physical quantities have
been determined and evaluated is it possible to evaluate if RCFD might be a reliable method
to determine an absolute 2D dose distribution.

Toon meer
OrganisatieDe Haagse Hogeschool
OpleidingTISD Technische Natuurkunde
AfdelingAcademie voor Technologie, Innovatie & Society Delft
PartnersVSL
Jaar2013
TypeBachelor
TaalEngels

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