Beta dosimetry for radioimmunotherapy of cancer using labeled antibodies

Starting with the tabulation of scaled monoenergetic electron dose point kernels F in water, according to the calculations of Berger, we have developed analytic approximations that facilitate the task for convolving F with beta spectra of specific nuclides to derive their dose point kernels J. J is well fitted by a single log-normal distribution, involving three independent parameters. For large atomic numbers, the addition of an exponential function near the origin is required. The radiation dose distribution D in a homogeneous medium of soft tissue with an activity distribution C is given by the convolution of J with C. Computer programs using fast Fourier transform techniques have been developed to evaluate the convolution efficiently. To study the perturbation of tissue inhomogeneity for D, we have used a point source of 32P and measured the increase in backscattered dose from a polystyrene/aluminum interface simulating soft tissue/bone. We have also measured the decrease in dose at a polystyrene/air interface.