Page 200 - 89Zr-Immuno-PET:Towards a Clinical Tool to Guide Antibody-based Therapy in Cancer

Chapter 10
The radiation exposure due to 89Zr-immuno-PET is ~0.6 mSv/MBq
In Chapter 2, biodistribution and radiation dose of 89Zr-cmAb U36 were investigated in the cohort of 20 patients with head and neck cancer. The normal organ with the highest absorbed dose was the liver (mean dose: 1.25±0.27 mSv/ MBq in men and 1.35±0.21 mSv/MBq in women, due to clearance and catabolism of antibodies via the liver), thereafter followed by kidneys, thyroid, lungs and spleen. The mean absorbed red marrow dose was 0.07±0.02 mSv/MBq and 0.09±0.01 mSv/MBq in men and women, respectively. Measured excretion via the urinary tract was less than 3% during the first 3 days p.i.. The mean effective dose was 0.53±0.03 mSv/MBq in men and 0.66±0.03 mSv/MBq in women.
Similar values for the mean effective dose have been reported in the literature for 89Zr-cetuximab (0.61 mSv/MBq) (1) and 89Zr-trastuzumab (0.48 mSv/MBq) (2).
Based on these studies, a typical 89Zr-immuno-PET study, performed with an injected dose of 37 MBq, results in an effective dose of 22.2 mSv (plus 3mSv for each low dose CT scan). The radiation exposure due to 89Zr-immuno-PET is relatively high (compared to 4.8 mSv for 18F-FDG-PET, ~13.3 mSv for a diagnostic CT-scan of the neck, thorax and abdomen (depending on the protocol), 0.04 mSv for a chest X-ray, 0.05 mSv for a transatlantic flight) (3). The average lifetime risk of dying from cancer due to radiation exposure of 1 mSv is estimated at 1 in 20.000 for a 40-year old person (4). However, this risk should be seen in perspective for patients who already have a form of cancer. In general, the radiation safety principle ‘as low as reasonably achievable (ALARA)’ should be applied (5).
Tumor uptake can be visualized with 89Zr-immuno-PET
Chapter 3 describes the performance of immuno-PET with 89Zr-cmAb U36 for the same cohort of twenty patients with HNSCC as in Chapter 2. The target antigen of cmAb U36, CD44v6, is abundantly expressed in HNSCC.
Prior to surgery, all patients were evaluated by computed tomography (CT) and/or magnetic resonance imaging (MRI) and 89Zr-immuno-PET. Imaging results were compared with histopathological findings per neck side (left or right), as well as per lymph node level (6 levels per side). All primary tumors were visualized on 89Zr-immuno-PET (n=17). Lymph node metastases were identified in 18 of 25 positive levels (sensitivity 72%) and in 11 of 15 positive sides (sensitivity 73%). For CT/MRI, sensitivity per level and per side was 60% and 73%, respectively. 89Zr-immuno-PET corresponded with pathology in 112 of 121 operated levels
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