Analysis of dosimetric and radiation safety results of seventeen patients treated with radioimmuno therapy using Iodine 131—Tositumomab for non-Hodgkin’s lymphoma

Abstract

12513 Background: Radioimmunotherapy using radioactive Iodine -131 labeled radioimmuno conjugate called Tositumomab has been used in the treatment of non-Hodgkin’s lymphoma. Radiation dosimetry and safety aspects of this treatment modality are very critical for successful implementation of this treatment. Methods: Since year 2001, we have treated 17 patients using I-131-tositumomab. There were 11 female and 6 male patients at age range of 40 to 82 years. Patient specific dosimetry was performed on all the patents using a tracer dose of I-131. The whole body counts were performed after infusion of 5.0 mCi of I-131-tositumomab and whole body counts were taken at 0, 48 and 178 hours. The total body residence time (TBRT) for 37% of the activity to stay in the body was determined by graphical method. The activity in mCi, for delivering 65 cGy or 75 cGy whole body dose, was calculated based on the TBRT and patient’s weight. Based on the measured exposure rate, we have calculated the total effective dose equivalent (TEDE) to the public. The patients were released to home with radiation safety instructions if TEDE delivered to the public was less than 5.0 mGy. We have studied the platelet count recovery time for all the patients, following treatment. Results: The calculated TBRT ranged from 85 to 175 hours and the the mCi/Kgm varied from 1.4 to 0.6, related inverse proportion with TBRT. For both group of patients, treated with total body dose of 65 cGy and 75 cGy, the mCi/Kgm was the same, for TBRT values exceeding 100 hours. The TEDE to public varied from 1.02 to 3.22 mGy, while the exposure rate measured on the patient at 1 meter was less than the permissible value reported in the literature for safe release. Conclusion: The above results show that the patients can be treated as outpatient using I-131 -tositumomab with radiation safety restrictions lasted for one week. The radiation exposure to the public was less than the maximum permissible dose equivalent. No significant financial relationships to disclose.