Radiation internal dosimetry in radioimmunotherapy using 131I-rituximab

Radioimmunotherapy (RIT) is a promising approach for targeted therapy to treat intractable cancer because radionuclides are delivered more selective to tumor using monoclonal antibody, RIT can be used clinical practice with administration of murine anti-CD20. In this study, the absorbed dose of total body and red marrow of patient enrolled in RIT study was calculated. Ten patients were enrolled in Korea cancer center hospital (KCCH). A Siemens Symbia T2 SPECT/CT scanner was used throughout to acquire planar data. Time-activity curve (TAC) was derived from actual whole-body gamma camera imaging. TAC was fitted using the bi-exponential function and was used for calculation of the residence time and the value of total body activity and administered dose. Total activity of whole blood sampled at imaging time was measured using well counter. The estimation of red marrow information value (weight and HCT) was used residence time of total body and whole blood. Dose estimation total body and red marrow were calculated using MIDOSE 3 program. When we gave initial dose of 200 mCi, absorbed dose was within the range of ICRP provision which is 200 cGy for bone marrow. In this present study, absorbed dose was calculated and confirmed within the range of 200 cGy for bone marrow. This dosimetry information would be helpful for the further RIT planning of patients.