| Summary: | The Medical Internal Radiation Dose (MIRD) protocol has provided a solid foundation
over the years for calculating the internal absorbed dose but as for providing an assessment
that is specific to the individual patient's organ/tumor anatomy, it falls short.
Various methods have been proposed to overcome the shortcomings of the MIRD protocol,
but each has its own limitations.
Quantitative SPECT proves to be the most desirable option for determining dose
estimates, yet the prolonged scan times prevent SPECT from becoming a clinical protocol
in dosimetry. Given the time constraints of clinical SPECT, planar quantitative imaging
has proved a popular choice for dosimetry studies, but the resulting dose overestimates
may prevent maximum therapy from being achieved.
Proposed here is a protocol that contends to be clinically feasible, patient-specific, and
promising in its results. This protocol combines the benefits of both quantitative planar
and SPECT imaging. By maintaining the majority of scans as planar yet incorporating
the benefits of attenuation corrected SPECT scans, a more accurate, yet attainable
clinical protocol can be achieved. The 2 or more SPECT scans suggested make use of a
Gadolinium-153 transmission source so that a simultaneous emission/transmission scan
provide a patient-specific, attenuation corrected SPECT image. The SPECT data is then
used to constrain the planar data, resulting in a more accurate dose estimate than would
arise from planar alone. Phantom experiments demonstrate that the errors in absorbed
dose estimates have improved from an average of 159% for planar methods alone to 14%
by the addition of a SPECT constraint. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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