Abstract
1401
Objectives Patient-specific optimization of treatment using dosimetry based on pre-therapeutic images is a fundamental strength of RPT. Radiobiological and quantitative imaging-based dosimetry tools are now available that enable rational implementation of combined targeted RPT. Optimal implementation should simultaneously account for radiobiological normal organ tolerance while optimizing the ratio of two different radiopharmaceuticals in order to maximize tumor control. We present such a methodology and apply it to hypothetical myeloablative treatment of NHL patients using 131I-tositumomab (B) and 90Y-ibritumomab tiuxetan (Z).
Methods The range of potential administered activities (AA) is limited by the normal organ maximum tolerated biologic effective doses (MTBEDs) arising from the combined radiopharmaceuticals. Lungs, liver, and kidneys were considered as possible dose limiting organs. By plotting the limiting normal organ constraints as a function of the AAs and calculating tumor biological effective dose (BED) along the normal organ MTBED limits, the optimal combination of activities is obtained. The model was tested using previously acquired patient normal organ and tumor kinetic data and MTBED values taken from the literature.
Results The average AA values based solely on normal organ constraints were (19.0 ± 8.2) GBq with a range of 3.9 - 36.9 GBq for B, and (2.77 ± 1.64) GBq with a range of 0.42 - 7.54 GBq for Z. Tumor BED optimization results were calculated and plotted as a function of AA using patient normal organ kinetics for the two radiopharmaceuticals. Results included AA ranges which would deliver 95 % of the maximum tumor BED, which allows for informed inclusion of clinical considerations, such as a maximum allowable 131I administration.
Conclusions A rational approach for combination RPT has been developed within the framework of a proven 3-dimensional personalized dosimetry software, 3D-RD, and applied to the myeloablative treatment of NHL.
Research Support NIH