Magnetically-enhanced reduction of radiation dose to bone marrow from bone-avid radiopharmaceuticals

In an effort to offset low uptake of tumor-avid radiopharmaceuticals, radionuclides which emit high average-energy electrons have been proposed as radiolabels for therapy. Unfortunately, use of these radionuclides (many of which are bone-avid) increases myelosuppression on a per-decay basis. In order to allow for the utilization of larger injected doses of this class of high-energy beta emitters, we propose the application of a storing static homogeneous magnetic field to constrain the beta particles to regions close to bone surfaces. To assess the potential bone marrow dose reduction resulting from utilization of this technique, we performed Monte Carlo simulations to evaluate the effect of magnetic fields on the energy deposition from beta particles in long bone marrow cavities. Results indicate that application of a 10 Tesla magnetic field can decrease the total radiation dose from bone-avid tracers to marrow located in shafts of human long bones by up to 14%. More significantly, however, the penetration depth of high-energy electrons from the bone surface into the marrow can be reduced by up to 72.1%. Indeed, some areas in the center of long-bone marrow cavities are predicted to be almost completely protected from radiation exposure due to emitted electrons. Protection of marrow inmore » areas distal from the inner bone surface has previously been shown to facilitate relatively rapid recovery from anemia produced by radiation damage to trabecular marrow (without marrow transplantation). Magnetically-enhanced protection of bone marrow, therefore, may allow administered doses of high-energy beta-emitting radionuclides (such as Yttrium-90) to be increased. Thus, amounts of radiation dose absorbed by both soft and calcified tissue tumors may also be increased. It is possible, therefore, that this technique might, in part, aid in realization of the promise of radionuclide therapy by permitting the delivery of greater levels of absorbed radiation dose to tumors.« less