Prospective individual dosimetry for iodine-131 radioimmunotherapy of non-hodgkins lymphoma

Full text: A pilot study of 131I-rituximab, anti CD-20 chimeric monoclonal antibody therapy of relapsed/refractory non-Hodgkins lymphoma (NHL) commenced at Fremantle Hospital in April 1999. Our technique for individual prospective dosimetry was developed and validated in 32 patients enrolled in a formal phase II clinical trial. A selected patient cohort (n=12) underwent an extended dosimetry protocol, which included post-therapy imaging. The mean total body dose prescribed was 0.75 Gy. Radiation absorbed dose to red marrow was predominantly due to whole body irradiation by 131I photons and our dosimetry protocol measured total body retention without a requirement for blood sampling. The average total body effective half-life was 86 hours (range 44-107). Post therapy CT/SPECT semi-quantitative fusion imaging using the GE HawkEye system performed at day 5 after administration, showed intense concentration of 131I-rituximab in diseased paraortic and inguinal nodes with target/background ratio in the range 1:3-1:10. Supraclavicular or axillary nodes were, however, not reliably visualized and target to background ratio at these sites was low (< 1:2). Radioimmunotherapy was very well tolerated in our patient population of relapsed/refractory NHL and clinical outcome was excellent objective response rate (ORR) 78%, complete remission (CR) 50% (n=32). Significantly, none of our patients experienced grade IV haematological toxicity using our dosimetry protocol, which compares most favourably with the 10-25% incidence reported in studies of commercial NHL radioimmunotherapy agents being trialed in the US. Copyright (2002) The Australian and New Zealand Society of Nuclear Medicine Inc