Objective: The 4.2-day half-life of 124 I favors its use for positron emission tomography (PET) of monoclonal antibodies (mAbs).

Small lithium formate EPR (electron paramagnetic resonance) dosimeters (diameter 3 mm, height 2 mm) were produced and employed for 2D dosimetry of stereotactic radiosurgery (SRS). An anthropomorphic head phantom with an in-house made insert holding 45 lithium formate dosimeters was used. A spherical target was outlined centrally in planning CT images of the head and an SRS dose plan with three arcs was made using the iPlan planning system. Beam collimation was achieved with the BrainLAB m3 micro-MLC. The minimum target dose was 15 Gy. The planned dose distribution was compared to measurements. For dosimetry, a dosimeter calibration series was generated with doses from 1 to 20 Gy. At the treatment unit, three replicate measurement series were performed. The measurements gave on average 2.2% lower dose at the plateau of the dose distribution compared to the dose plan. Larger differences were seen in the penumbra, where the dose plan underestimated the dose gradients. By repeated measurements, the systematic and random error in the SRS delivery was estimated to less than 1 mm. In conclusion, the planning system produced an intracranial dose distribution with tolerable accuracy. Furthermore, small lithium formate EPR dosimeters were useful for measuring SRS dose distributions.

Purpose: To estimate tumor targeting and radiation dose in mice receiving I‐124‐labeled anti‐CEA (Carcinoembryonic Antigen) intact monoclonal antibody. Use of I‐124 as a PET emitter is complicated by high‐energy photons (603 keV and 723 keV at 63% and 10% respectively) emitted along with the positrons (23%). Method and Materials: Intact monoclonal antibody cT84.66 was labeled with I‐124 and injected via tail vein into nude mice bearing LS174T human colon tumors (0.04 to 0.19 g). PET imaging was performed using the Siemens MicroPET RF scanner at seven time points out to 8 days post‐injection. Standard energy window of 350–750 keV was employed. Average voxel values from organ volumes of interest were used to determine relative magnitudes of activity in tumor, liver, heart (blood) and whole body. Absolute activities were calculated by normalizing these PET data to dissection results at the last time point. Bi‐exponential functions were fitted to resultant activity vs time curves and integrated to establish à values and residence times. Organ‐to‐organ S factors were determined by Monte Carlo analysis of I‐124 in a 20g digital mouse phantom. Organ dose was then estimated as the matrix product of SÃ. Results: Tumors were visualized within one day of injection. Average residence times for blood, tumor, liver and whole body were 45, 6.5, 7.0 and 86 hours respectively. Mean dose for the tumors was 3.3 Gy/MBq; associated liver and whole body average values were only 0.60 and 0.31 Gy/MBq respectively. Conclusions: Small colon tumors can be PET‐imaged in nude mice receiving the I‐124 anti‐CEA antibody cT84.66. By normalizing voxel results to those obtained at sacrifice, quantitative I‐124 uptakes can be measured and used to generate residence times. Ratios of tumor/liver and tumor/whole body dose were approximately 5 and 10 respectively.