De-identification of DICOM dates
The resulting DICOM dates are meaningless yet preserve the relative temporal distance between studies for a patient
De-identification of dates uses the DICOM standard “Retain Longitudinal With Modified Dates Option” which allows dates to be retained as long as they are modified from the original date. Date and Date-Time fields in TCIA DICOM image headers are de-identified by normalizing to a base date of January 1, 1960 and then shifted by the number of days between the original Study Date and an "anchor date". The anchor date for APOLLO is the Date of Diagnosis. The choice of '1960' was arbitrary, but it allows one to ensure that the dates in de-identified DICOM files have been properly de-identified as anything not around that year would be suspect.
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<e en="T" t="00080020" n="StudyDate"> @dateinterval(StudyDate,diagnosisdate,PatientID,@NORMDATE)</e>
Insertion of computed "Days from registration" value
The inserted "Days from registration" value can be compared with similar values in the APOLLO 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 by the CTP software (using the diagnosis date in the CTP lookup table at the submission site) and automatically stored in the DICOM tag (0012,0052) Longitudinal Temporal Offset from Event with the associated tag (0012,0053) Longitudinal Temporal Event Type set to “Days from registration”. The days from diagnosis links the imaging data to the clinical data for a given subject. The CTP code for this is:
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<e en="T" t="00120053" n="LongitudinalTemporalEventType">@always()@param(@LTET)</e> (where LTET is defined as DIAGNOSIS)
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.
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