Backscattering and transmission through a high Z interface as a measure of electron beam energy.

The ratio of electron beam transmission (Tr) and backscattering (Bs) is used as a measure of beam energy. With a proper thickness of high Z medium placed at the surface of a low Z homogeneous medium, it is observed that the function log(Tr/Bs) is a linear function of electron energy. This method is applied to electrons produced with scattering foil and pulse-swept (scanned) beams for the nominal energies ranging from 6 to 20 MeV. This technique provides a unique alternative method which is easy, simple, and accurate within +/- 3% for estimation of electron beam energy.

Spatial distribution of bremsstrahlung in a dual electron beam used in total skin electron treatments: errors due to ionization chamber cable irradiation.

The spatial distribution of the bremsstrahlung dose in total skin electron therapy and large electron fields has been assumed to be symmetric along the match line; however, the measured data in the entire plane have not been available. Das et al. ["Spatial distribution of bremsstrahlung in total skin electron irradiation," Med. Phys. 19, 810 (1992)] reported the ion-chamber measured bremsstrahlung data in the Stanford six-field technique and found that the bremsstrahlung dose profile was 2.5 times greater in the caudal plane (beam facing toward floor) as compared to the cephalic plane. This observation was recently quoted by Klevenhagen [Physics and Dosimetry of Therapy Electron Beams (Medical Physics, Madison, WI, 1993)]. Further study using thermoluminescent dosimeters and careful measurements using ion chambers showed that the bremsstrahlung radiation was indeed symmetric at the match line as theoretically predicted and was not a function of the beam angle or the type of floor. The earlier observations of Das et al. were found to be due to cable effects. Ionization chamber cable response in a large electron field and the associated errors in the bremsstrahlung distribution are presented. It is suggested that a cable-free dosimeter should be used for measuring low levels of bremsstrahlung radiation in large electron fields and at extended distances.

Pharmacokinetics of indium-111 labeled 10-3D2 antibreast-tumor antibody in patients.

In a program to investigate patient pharmacokinetics of labeled anti-tumor antibodies, a study of the 10-3D2 anti-breast tumor antibody was conducted. The F(ab')2 fragment, coupled with DTPA, was radiolabeled with indium-111 and 1 mg (37 MBq, or 1 mCi) administered to each of 7 patients with documented or suspected breast carcinoma. Abnormal accumulations of radioactivity were observed in only one patient even though 5 had evidence of disease at the time of imaging. Despite the reported absence of circulating antigen to this antibody, sera from one patient showed evidence of a high molecular weight immune complex by size exclusion HPLC. However, this patient had detectable circulating HAMA, which cannot be excluded as the cause of such immune complex. Urine excretion of radioactivity varied greatly from patient to patient (from 2-34% ID within the first day) but the mean value (0.22% ID/hour) was equal to that seen by us in previous studies. The biodistribution of the label was found to be unusual in that kidney levels increased in all patients during the first day and, in particular, liver radioactivity levels decreased in all patients.

Long-term biodistribution in tumored mice of murine and chimeric B72.3-IgG antibody radiolabeled with 114mIn via both DTPA and a macrocyclic chelator.

To assess the possibilities of using 114mIn as a therapeutic agent, the long-term biodistribution of 114mIn was studied, in tumor-bearing nude mice, after injection of labeled monoclonal antibody (MoAb) B72.3 IgG, either DTPA-coupled murine, DTPA-coupled chimeric, or macrocycle-coupled chimeric antibody. Although the biodistributions in all cases were similar, there were important differences. The use of DTPA-coupled chimeric antibody led to higher concentrations of radioactivity in tumor, and to lower concentrations in liver and bone, as compared to DTPA-coupled murine antibody. The use of macrocycle-coupled chimeric antibody led to higher concentrations of radioactivity in the liver and in bone as compared to the DTPA-coupled chimeric antibody. However, in this case there were no significant differences in tumor uptake or clearance. Radiation doses were calculated based on the organ retention and by neglecting source-to-target contributions. Radiation dose distribution was marginally favorable for therapy in the group injected with DTPA-coupled chimeric antibody.