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D'Arienzo M.,SantAndrea Hospital | D'Arienzo M.,ENEA | Cicone F.,University of Rome La Sapienza | Chiacchiararelli L.,SantAndrea Hospital | And 3 more authors.
Cancer Biotherapy and Radiopharmaceuticals | Year: 2012

Aim of the present article was to perform three-dimensional (3D) single photon emission tomography-based dosimetry in radioimmunotherapy (RIT) with 90Y-ibritumomab-tiuxetan. A custom MATLAB-based code was used to elaborate 3D images and to compare average 3D doses to lesions and to organs at risk (OARs) with those obtained with planar (2D) dosimetry. Our 3D dosimetry procedure was validated through preliminary phantom studies using a body phantom consisting of a lung insert and six spheres with various sizes. In phantom study, the accuracy of dose determination of our imaging protocol decreased when the object volume decreased below 5 mL, approximately. The poorest results were obtained for the 2.58 mL and 1.30 mL spheres where the dose error evaluated on corrected images with regard to the theoretical dose value was-12.97% and-18.69%, respectively. Our 3D dosimetry protocol was subsequently applied on four patients before RIT with 90Y-ibritumomab-tiuxetan for a total of 5 lesions and 4 OARs (2 livers, 2 spleens). In patient study, without the implementation of volume recovery technique, tumor absorbed doses calculated with the voxel-based approach were systematically lower than those calculated with the planar protocol, with average underestimation of-39% (range from-13.1% to-62.7%). After volume recovery, dose differences reduce significantly, with average deviation of-14.2% (range from-38.7.4% to +3.4%, 1 overestimation, 4 underestimations). Organ dosimetry in one case overestimated, in the other underestimated the dose delivered to liver and spleen. However, both for 2D and 3D approach, absorbed doses to organs per unit administered activity are comparable with most recent literature findings. © 2012, Mary Ann Liebert, Inc.

Cicone F.,University of Rome La Sapienza | D'Arienzo M.,ENEA | D'Arienzo M.,University of Rome La Sapienza | Carpaneto A.,SantAnna Hospital | And 4 more authors.
Cancer Biotherapy and Radiopharmaceuticals | Year: 2013

Objective: To assess the impact of nonuniform dose distribution within lesions and tumor-involved organs of patients receiving Zevalin®, and to discuss possible implications of equivalent uniform biological effective doses (EU-BED) on treatment efficacy and toxicity. MATLAB™ -based software for voxel-based dosimetry was adopted for this purpose. Methods: Eleven lesions from seven patients with either indolent or aggressive non-Hodgkin lymphoma were analyzed, along with four organs with disease. Absorbed doses were estimated by a direct integration of single-voxel kinetic data from serial tomographic images. After proper corrections, differential BED distributions and surviving cell fractions were estimated, allowing for the calculation of EU-BED. To quantify dose uniformity in each target area, a heterogeneity index was defined. Results: Average doses were below those prescribed by conventional radiotherapy to eradicate lymphoma lesions. Dose heterogeneity and effect on tumor control varied among lesions, with no apparent relation to tumor mass. Although radiation doses to involved organs were safe, unexpected liver toxicity occurred in one patient who presented with a pattern of diffuse infiltration. Conclusion: Voxel-based dosimetry and radiobiologic modeling can be successfully applied to lesions and tumor-involved organs, representing a methodological advance over estimation of mean absorbed doses. However, effects on tumor control and organ toxicity still cannot be easily predicted. © Copyright 2013, Mary Ann Liebert, Inc.

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