Feasibility of bremsstrahlung dosimetry for direct dose estimation in patients undergoing treatment with ^sup 90^Y-ibritumomab tiuxetan

• Published in: European journal of nuclear medicine and molecular imaging 2012-06, Vol.39 (6), p.956
• Main Authors: Arrichiello, C, Aloj, L, Mormile, M, D'ambrosio, L, Frigeri, F, Caracò, C, Arcamone, M, De Martinis, F, Pinto, A, Lastoria, S
• Format: Article
• Language: English
• Subjects: Immunotherapy; Lymphoma; Medical imaging; Nuclear medicine; Radiation therapy; Radiology
• ISSN: 1619-7070; 1619-7089
• DOI: 10.1007/s00259-011-2040-5

Radioimmunotherapy with ^sup 90^Y-ibritumomab tiuxetan has been used successfully used in the treatment of CD20-positive non-Hodgkin's lymphoma (NHL). Pretherapy imaging with ^sup 111^In-ibritumomab tiuxetan has been used in provisional dosimetry studies. Posttherapy imaging of ^sup 90^Y-ibritumomab tiuxetan for clinical use is appealing as it would simplify the data acquisition process and allow measurements of actual doses absorbed during treatment. The study included 29 patients with non-Hodgkin's lymphoma, of whom 16 (group I) received a pretherapy ^sup 111^In-ibritumomab tiuxetan diagnostic study and ^sup 90^Y-ibritumomab tiuxetan treatment 1 week later, and 13 (group II) received only ^sup 90^Y-ibritumomab tiuxetan treatment. Planar imaging and blood sampling were performed in all patients. The doses absorbed by organs at risk were calculated using a whole-body average attenuation correction factor (relative dosimetry approach) and, in the case of the ^sup 111^In-ibritumomab tiuxetan image sets, also using organ-specific attenuation correction factors (absolute dosimetry method). Red marrow absorbed doses were based on gamma counting of blood samples. The estimated red marrow absorbed doses from ^sup 111^In and ^sup 90^Y data were equivalent. In all cases, the doses absorbed by organs at risk were found to be within prescribed limits. The relative dosimetry approach applied to both the ^sup 90^Y and ^sup 111^In data significantly underestimated the doses relative to those obtained with the ^sup 111^In absolute dosimetry method which is generally accepted as the reference method (MIRD 16). In the case of ^sup 111^In, the relative dosimetry approach values were highly correlated (R ^sup 2^=0.61) with the reference method values. Relative dosimetry estimates may be adjusted multiplying by a correction factor of 2.8. The ^sup 90^Y-ibritumomab tiuxetan relative dosimetry data correlated poorly with the reference method values (R ^sup 2^=0.02). Based on patient-specific dosimetry, the administered activity may be increased by an average factor of 2.4, indicating that most patients could be undertreated. The relative dosimetry approach based on planar imaging largely underestimates doses relative to reference values. Dosimetry based on planar bremsstrahlung imaging is not a dependable alternative to ^sup 111^In dosimetry.[PUBLICATION ABSTRACT]