POST-TRACER AND POST-THERAPY IMAGING USING A NEW SPECT-CT INTEGRATED SYSTEM FOR

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. I-131 labeled radioimmunotherapy (RIT) is showing great promise in the treatment of non-Hodgkin s lymphoma (NHL). To make advances towards individualized treatment planning in radionuclide therapy, it is necessary to establish reliable dose-response relationships for target tissue and dose-toxicity relationships for normal tissue. Thus far, most clinical I-131 radionuclide therapy studies have shown an absent or rather weak relationship between radiation absorbed dose and tumor response or critical organ toxicity. The lack of better correlation is possibly due to inaccuracies in absorbed dose estimation methods used thus far. This warrants the effort towards developing and evaluating highly accurate methods for imaging based dosimetry. This is a prospective pilot study evaluating the potential value of a new SPECT-CT integrated system for imaging based dosimetry in Non-Hodgkins lymphoma patients treated with I-131 tositumomab (Bexaar) radioimmunotherapy (RIT). We aim to determine the value of concurrent SPECT-CT imaging in precise anatomic localization of areas of abnormal radiotracer activity compared to planar scintigraphy and conventional SPECT. The SPECT-CT images will be used to carry out highly accurate patient specific 3-dimensional dosimetry in tumors and bone marrow using a computer algorithm recently implemented by our group. Five patients over 21 years of age of both genders and all ethnic and racial groups who are scheduled to undergo the Bexaar treatment will be asked to volunteer for between 3 to 6 scans on the new SPECT-CT system following the tracer and/or the therapy administration of Bexaar. The imaging is based on the radioactivity that is administered as part of the RIT treatment and the patient will not be injected with any additional radioactivity due to the research aspect of the proposed study. If the feasibility of using the new system for highly accurate dosimetry is established by the present project, it can be used in the future with a large number of subjects to establish dose-response and dose-toxicity relationships. Establishment of such relationships and the capability to carry out highly accurate imaging based dosimetry prospectively, will allow physicians in the future to tailor the treatment regimen on a patient-by-patient basis to deliver the optimum dose to the tumor while avoiding toxicity to critical organs. Highly accurate bone marrow dosimetry may also allow for the inclusion of additional patients who are presently excluded from this treatment because of the present criteria that they have < 25% bone marrow involvement.