Aim: To analyze the inter-fraction,
intra-fraction uncertainties and to verify the delivered total dose with
planned dose in the combined intracavitary-interstitial brachytherapy of
gynaecological cancer patients using microMOSFET in-vivo
dosimeter. Materials and Methods: Between May 2014 and March 2016, 22 patients
who underwent brachytherapy treatments with an applicator combination of CT/MR
compatible tandem, ring and Syed-Neblett template-guided rigid needles were
included in this study. Specially designed microMOSFET, after calibration, was
used to analyze the variations in dosimetry of combined
intracavitary-interstitial application. Results: The standard deviation for
Inter-fraction variation among 22 combined intracavitary interstitial
applications ranged between 0.86% and 10.92%. When compared with the first
fraction dose, the minimum and maximum dose variations were −9.5% and
26.36%, respectively. However, the mean doses varied between −5.95%
and 14.49%. Intra-fraction variation, which is the difference of TPS calculated
dose with first fraction microMOSFET-measured dose ranges from −6.77%
to 8.68%. The variations in the delivered total mean dose in 66 sessions with
planned doses were −3.09% to 10.83%. Conclusions: It is found that
there was a gradual increase in microMOSFET measured doses as compared to the
first fraction with that of subsequent fractions in 19 out of 22 applications.
Tumor deformation and edema may be the influencing factors, but the applicator
movements played a major role for the variations. We find that the microMOSFET
is an easy and reliable system for independent verification of uncertainties
during ICBT-ISBT treatments.
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