THE NOVEL TECHNOLOGY OF HYBRID IMAGING (COMBINED PET/CT AND SPECT/CT) IN CANCER - CLINICAL APPLICATIONS
Imaging plays an important role in the noninvasive evaluation of physiology and anatomy of tumors and has a major impact in management of cancer patients. Anatomic imaging modalities, such as CT, provide the main morphologic information for correct definition and localization of malignant tumors. Nuclear medicine is the provider of physiologic data, based on increased glucose utilization or other metabolic changes in malignant cells.
Non-specific targeting of radiopharmaceuticals and device-related limitations hamper, however, nuclear medicine. Also, CT does not always allow for the correct characterization and definition of suspected lesions and tumor size does not necessarily correlate with malignancy. The need for complementary anatomic and physiologic cancer evaluation has emerged from everyday clinical requirements.
The initial clinical experience with a new hybrid imaging technology (Hawkeye VG & Discovery LS, GE Medical Systems) for simultaneous anatomic (CT) and functional (nuclear medicine and PET) acquisition during a single imaging session will be discussed.
Hybrid imaging improves interpretation accuracy of the nuclear medicine procedure in over 40% of cancer patients. Combined imaging enables a more precise localization of malignant lesions, excludes disease in areas of radioactivity unrelated to cancer and also detects additional, previously unsuspected sites of tumors. Hybrid imaging also improves the accuracy of CT reading in over 15% of patients, mostly by retrospective detection of cancer sites previously missed. The new technology permits the localization of hypermetabolic changes seen on nuclear medicine procedures to precise anatomic regions, thus guiding further invasive biopsy procedures or follow up imaging studies.
Hybrid imaging results in a more correct staging of cancer and assessment of the true relationship between the presence of viable cancer in a tumor mass after treatment. This modality has therefore a clinical impact on treatment planning leading to inter- and intramodality therapeutic modifications such as sparing patients unnecessary surgery, referral to previously unconsidered treatment options and changing the planned surgical, chemo- or radiotherapy approach.
Hybrid imaging using PET/CT and SPECT/CT appears to be a promising new clinical tool for diagnosis and staging of cancer patients, for therapy planning, monitoring response to treatment and diagnosis of tumor relapse. It combines the functional ability of nuclear medicine techniques for detection of viable cancer with the accurate localization provided by CT.