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When to do a PET

Timing in life is everything. Here are some factors to consider when ordering a PET or
PET/CT scan. If you have any questions in regards to PET or PET/CT in relation to any
of the below treatment situations, please do not hesitate to call us.

I. Chemotherapy:
     A. During therapy:
           1. Continuously administered - PET/CT can be done any time. PET/CT in this case
               measures both tumor cell death and suppression of remaining viable cell activity
           2. Cyclic administration - best time to do PET/CT is 1-3 days before next cycle                begins.
     B. At completion of planned regimen:
           1. 4-6 weeks following last chemotherapy (or 1-2 days before additional therapy
               would be employed).

II. Radiation therapy and chemoradiation therapy:
     A. As primary therapy:
           1. At 3-4 weeks after completion - assess adequacy of therapy (is all the hyper-
               metabolism abated? If not, more therapy is needed). Exceptions based on
               chemotherapy protocol.
           2. At 3-4 months - verify completeness of response.

III. Surgery:
     A. Prior to surgery - 1-3 days prior to procedure.
     B. After surgery - 1-2 weeks preferred, but can be sooner.

IV. Bone marrow stimulants - by stimulating increased production of circulating cells in the bloodstream the uptake of FDG in the precursor cells increases 5-10 fold:
     A. Procrit - wait 1-2 days after administration before doing a PET/CT scan.
     B. Neupogen - wait 7-10 days after administration before a PET/CT scan.
     C. Neulasta - wait 10-17 days after administration before performing a PET/CT scan.

V. Caveats:
     A. General answers - the above answers may not fit every clinical situation. Often, timing
         of PET/CT scanning needs to be individualized. The referring physician should call and
         discuss the patient's care with an MRP physician.
     B. Evolution of cancer therapy - timing of PET scanning must continue to evolve as the
          treatment of cancer evolves.
     C. The above information is based upon Metro Region PET Center's clinical experience
         from reading more than 19,000 PET scans. Research for evidence based decisions is
         currently ongoing.

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