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This technique de-identifies the dates while preserving the longitudinal relationship between dates. Therefore, a researcher won’t know the precise date the scan occurred, but if a follow up scan was performed 120 days later, that same 120 day difference between scans of a subject will exist in the TCIA images. Dates that occur in DICOM tags other than Date or Date-Time fields are removed. An example of this would be a date entered into the Series Description field. If the date is associated with a library for Code Meaning then that date is preserved as the date would be required to look up the meaning in the correct version of the library. To show that the dates have been modified, the term “MODIFIED” is written into DICOM tag (0028,0303) “LongitudinalTemporalInformationModified”“LongitudinalTemporalInformationModified”.
Original dates will be first normalized to 01 January, 1960 and then offset relative to the date of registration. The CTP code for shifting the StudyDate is shown below:
<e en="T" t="00080020" n="StudyDate"> @dateinterval(StudyDate,diagnosisdate,PatientID,@NORMDATE)</e>
Insertion of computed "REGISTRATION"/Days offset from registration" value
The inserted "REGISTRATION" or "Days offset from registration" value can be compared with similar values in the NCTN clinical data to understand the clinical context of the imaging study
The number of days the study occurred relative to the date of registration is calculated
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(using the
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registration date as identified for each patient) and stored in the DICOM tag (0012,0052)
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Longitudinal Temporal Offset from Event with the associated tag (0012,0053) Longitudinal Temporal Event Type set to
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“REGISTRATION”. The value in the (0012,0052) DICOM tags is given in days as related to the date of registration which links the imaging data to the clinical data for a given subject.
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<e en="T" t="00120052" n="LongitudinalTemporalOffsetfromEvent">@always()@dateinterval(StudyDate,ddate,PatientID)</e>
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Insertion of "registration Year"
It is important for cancer researchers to know the timeframe for which the cancer was diagnosed to relate the prescribed cancer treatment or staging to what was available at that time.
In order to relate the treatments that were available at the time of the diagnosis, the year that the primary diagnosis was made is recorded in a CTP owned group 13 private tag as follows.
<e en="T" t="00131051" n="DiagnosisYear">@always()@lookup(PatientID,diagnosisdate)</e>
In a separate stage of the pipeline the diagnosisdate is truncated to be just the year that the diagnosis was made.
<e en="T" t="00131051" n="DiagnosisYear">@truncate(DiagnosisYear,-4)</e>
The approximate StudyYear can be calculated by adding the days from diagnosis in tag LongitudinalTemporalOffsetfromEvent to the DiagnosisYear.
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If these DICOM tags are not present, DICOM tag (0012,0050) Clinical Trial Time Point ID with the associated tag (0012,0051) Clinical Trial Time Point Description Attribute set to “Days offset from registration” provides this same information.
The normalized date workflow described above requires that diagnosis the registration date be present and this workflow does not handle the example where there no diagnosis the registration date is not present.