Abstract
BACKGROUND: Diffusing alpha-emitters radiation therapy ("Alpha-DaRT") is a new modality that uses alpha particles to treat solid tumors. Alpha-DaRT employs interstitial sources loaded with low activities of 224Ra , designed to release a chain of short-lived alpha-emitters, which diffuse over a few millimeters around each source. Alpha-DaRT dosimetry is described, to first order, by a framework called the "diffusion-leakage" (DL) model. PURPOSE: The aim of this work is to estimate the tumor-specific parameters of the DL model from in vivo studies on multiple histological cancer types. METHODS: Autoradiography studies with phosphor imaging were conducted on 113 tumors in mice from 10 cancer cell lines. An observable, referred to as the "effective diffusion length" Leff , was extracted from images of histological slices obtained using phosphor screens. The tumor and Alpha-DaRT source activities were measured after excision with a gamma counter to estimate the probability of 212Pb clearance from the tumor by the blood, Pleak(Pb) . RESULTS: The measured values of Leff are in the range of 0.2-0.7 mm across different tumor types and sizes. Pleak(Pb) is between 10 and 90% for all measured tumors, and it generally decreases in magnitude and spread for larger tumors. CONCLUSIONS: The measured values of Leff and Pleak(Pb) and associated dose calculations indicate that hexagonal Alpha-DaRT source lattices of ∼ 4-mm spacing with μCi -scale 224Ra activities can lead to effective coverage of the tumor volume with therapeutic dose levels, with considerable margin to compensate for local variations in diffusion and leakage.