Approach to radionuclide therapy dosimetry planning

Control of radiation dose absorbed in pathological volume represents one of the challenging issues in the implementation of radionuclide therapy (RNT). This paper presents new approach based on estimation of radiopharmaceutical (RP) accumulated activity value in tumor volume, based on planar scintigraphic images of the patient and calculated radiation transport using Monte Carlo method, including absorption and scattering in biological tissues of the patient, and elements of gamma camera itself. In our research, to obtain the data, we performed modeling scintigraphy of the vial with administered to the patient activity of RP in gamma camera, the vial was placed at the certain distance from the collimator, and the similar study was performed in identical geometry, with the same values of activity of radiopharmaceuticals in the pathological target in the body of the patient. For correct calculation results, adapted Fisher–Snyder human phantom was simulated in MCNP program. In the context of our technique, calculations were performed for different sizes of pathological targets and various tumors deeps inside patient's body, using radiopharmaceuticals based on a mixed β–γ-emitting (131I, 177Lu), and clear в-emitting (89Sr, 90Y) therapeutic radionuclides. Presented method can be used for adequate assessment of the absorbed dose in the regions of interest on the basis of patient planar scintigraphy.