Comparison of I-131 Radioimmunotherapy Tumor Dosimetry: Unit Density Sphere Model Versus Patient-Specific Monte Carlo Calculations

High computational requirements restrict the use of Monte Carlo algorithms for dose estimation in a clinical setting, despite the fact that they are considered more accurate than traditional methods. The goal of this study was to compare mean tumor absorbed dose estimates using the unit density sphere model incorporated in OLINDA with previously reported dose estimates from Monte Carlo simulations using the dose planning method (DPMMC) particle transport algorithm. The dataset (57 tumors, 19 lymphoma patients who underwent SPECT/CT imaging during I-131 radioimmunotherapy) included tumors of varying size, shape, and contrast. OLINDA calculations were first carried out using the baseline tumor volume and residence time from SPECT/CT imaging during 6 days post-tracer and 8 days post-therapy. Next, the OLINDA calculation was split over multiple time periods and summed to get the total dose, which accounted for the changes in tumor size. Results from the second calculation were compared with results determined by coupling SPECT/CT images with DPM Monte Carlo algorithms. Results from the OLINDA calculation accounting for changes in tumor size were almost always higher (median 22%, range -1%-68%) than the results from OLINDA using the baseline tumor volume because of tumor shrinkage. There was good agreement (median -5%, range -13%-2%) between the OLINDA results and the self-dose component from Monte Carlo calculations, indicating that tumor shape effects are a minor source of error when using the sphere model. However, because the sphere model ignores cross-irradiation, the OLINDA calculation significantly underestimated (median 14%, range 2%-31%) the total tumor absorbed dose compared with Monte Carlo. These results show that when the quantity of interest is the mean tumor absorbed dose, the unit density sphere model is a practical alternative to Monte Carlo for some applications. For applications requiring higher accuracy, computer-intensive Monte Carlo calculation is needed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90433/1/cbr-2E2011-2E0965.pd

A complete dosimetric characterization of two Sr-90-Y-90 dermatologic applicators

A complete dosimetric characterization of two Amershan Sr-90-Y-90 dermatologic applicators is described in this present work. The dosimetric parameters analyzed are: percentage depth dose curve, radial dose distribution, non-uniformity and asymmetry. Both applicators are planar-circular having 22.57 and 9.0 mm diameters. In the range where the percentage depth dose goes from 100% down to 20%, the measured percentage depth dose and that obtained by the Monte Carlo simulation have shown maximum discrepancy of 5.3% for both applicators. The radial dose distribution has been measured at several depths using a GafChromic (R) EBT QD+ films and it was also calculated by simulation. The discrepancies found did not exceed 5.9% up to the depth of 1.8 mm, where the percentage depth dose drops to 40% of the maximum. The maximum non-uniformity and asymmetry are 1.7% and 5.3% for the first applicator and 22.7% and 25.9% for the second applicator, respectively. Both applicators meet the specification for the maximum non-uniformity established by the adopted protocol, whose limit is 30%. As for the asymmetry the limit is 20% and the second applicator exceeded it in about 5.9%. (C) 2010 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Study of CT/MRI Mutual Information Based Registration Applied in Brachytherapy

The present work aims to include magnetic resonance imaging (MRI) in a Medical Image-based Graphical platfOrm Brachytherapy module (AMIGOBrachy) which coupled to the Monte Carlo N-Particle (MCNP6) code allows absorbed dose calculations. Computed tomography (CT) and MRI images were registered using mutual information algorithms to improve tissue segmentation potentially leading to a more accurate treatment planning system

Dosimetric evaluation in radiation synovectomy

Rheumatoid arthritis can manifest itself through synovitis, of which the knee is the common locale. The treatment using an intra-articular radioisotope injection has been applied in various countries. In this work, the dose of radioactive material absorbed in the joint is evaluated, taking into consideration the dose received in the articular cartilage and adjacencies using a three-dimensional voxel model representing the knee. The radioisotopes studied were Samarium-153 and Dysprosium-165. The results show that the synovial membrane receives 85 to 98% of the normalized dose taken from all voxels representative of the synovium. The following features of 153Sm and of 165Dy - its short physical half-life, the gamma emissions with low energy which allow monitoring the injection trough scintigraphy images, the possibility of binding themselves to macroaggregates that are retained in the joint, the high percentage of the effective dose spread in the synovial membrane - make these suitable radioisotopes for radiation synovectomy.<br>A artrite reumatóide pode se manifestar usualmente pela inflamação da membrana sinovial caracterizada como sinovite, sendo o joelho um substrato comum. O tratamento com a injeção intra-articular de radioisótopo, ou sinovectomia radioisotópica, vem sendo estudado. Neste trabalho será calculada a dose absorvida na sinóvia e nas adjacências através de um modelo tridimensional de voxels. Os radioisótopos estudados foram o Samário-153 e o Disprósio-165. Os resultados obtidos mostraram que uma taxa de dose máxima normalizada variando de 85 a 98% da dose máxima foi atingida em todos os voxels representativos da membrana sinovial. As características nucleares do Samário-153 e do Disprósio-165, associadas à taxa de dose efetiva recebida na articulação, fazem destes radioisótopos uma escolha na sinovectomia radioisotópica