The study was aimed to check the radiotherapy treatment accuracy and
definition of action levels during implementation of in vivo dosimetry as a
part of quality assurance program. The calibration and correction factors for
in vivo entrance dose measurements for six n-type Isorad semiconductor diodes
were determined as recommended by the European Society for Radiotherapy and
Oncology Booklet No. 5. The patients for in vivo measurements have been
divided in groups, according to the treatment site/techique, in order to
investigate and detect the groups where the uncertainty was larger or where a
systematic error occurred. The tolerance/action levels for all groups were
also defined and checked. In this study, the entrance dose measurements were
performed for total of 451 treatment fields, and 338 patients over one year
period. The mean value and the standard deviation for different groups were:
breast +1.0% ? 2.89%(1 SD), brain, and head and neck - +0.74% ? 2.04%(1 SD),
and isocentric pelvis and abdomen - +0.1% ? 2.86%(1 SD). All measurements -
+0.72% ? 2.64%(1 SD). In our experience, systematic in vivo dosimetry proved
to be a very useful tool for quality assurance of patient's plan and
treatment, both in detecting systematic errors and for estimating the
accuracy of radiotherapy treatment delivery.