microSTAR®ii User Manual v1.3 67
If there is a significant difference in values and the interval of time between the calibration used to
read the dosimeter, the test was very short, and the reader performance was stable, the difference may
be a result of uncertainty in labeled sensitivity of the nanoDot.
If the difference between these measurements is assessed for the whole population of nanoDots,
symmetry in the distribution would be expected. There would not be an appreciable positive or
negative bias.
Linear Dose Calculation Formula
(
)
=
×
The Corrected Sensitivity (S
corr
) can be thought of as the level of sensitivity that would have been
required to yield the known exposed dose level for the same counts and reader condition (i.e., using
the same calibration factor). Using substitution, the Corrected Sensitivity can be determined from the
following expression:
=
×
where S
lab
is the labeled sensitivity of each individual dosimeter and S
corr
is the sensitivity that would
have yielded the known exposed dose.
The Corrected Sensitivity (S
corr
) can also be expressed in the context of the SAF required to convert
the labeled sensitivity to the corrected sensitivity as shown below:
=
×
from which the SAF for an individual dosimeter can be estimated directly from the ratio of the
Measured Dose to Known Exposed Dose:
=
The uncertainty in sensitivity assessment at the time of manufacture of the screened nanoDot is known
to be ±3% under highly controlled test conditions, but because these estimates in the field are based
on actual readings for which the accuracy is specified to be within ±5.5%, the SAF computed under
these conditions can be as high as ±5.5%.
The more useful indicator of a systematic issue with sensitivity assessment is the comparison of the
minimum, maximum, and average percent difference (% Diff) between the labeled and corrected
sensitivity and whether there is a consistent and appreciable bias in the distribution of these results
across the population of dosimeters.
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