Radionuclide therapy with bone-seeking compounds: Monte Carlo calculationsof dose-volume histograms for bone marrow in trabecular bone

The purpose of the present work was to investigate how haematopoietic stem cell survival is affected by the differences in the dose distribution that arise from different radionuclides contained in bone-seeking radiopharmaceu ticals. This was carried out in three steps: (a) calculations of representa tive dose distributions in individual bone marrow cavities that are irradia ted by sources of Sr-89, Re-186, Sn-117m or Sm-153, uniformly distributed o n the bone surfaces; (b) assessment of the corresponding haematopoietic ste m cell survival and (c) a comparison of these results with results obtained using the assumption of a uniform dose distribution. Two different idealized models of the geometry of trabecular bone were form ulated, each consisting of an infinite array of identical elements. Monte C arlo simulations were used to generate dose-volume histograms that were use d to assess haematopoietic stem cell survival with two different assumption s about spatial cell distributions. Compared with a homogeneous dose distribution, the estimated cell survival was markedly higher for Sn-117m and Sm-153, and only slightly different for 89Sr and Re-186. The quantitative results differed between the two geometr ic models and the assumptions about spatial cell distribution, but the tren ds were the same. The results imply that it is necessary to include dose di stributions for individual bone marrow cavities in considerations concernin g bone marrow toxicity.