Design of experiments in medical physics: Application to the AAA beam model validation.

PURPOSE: The purpose of this study is to evaluate the usefulness of the design of experiments in the analysis of multiparametric problems related to the quality assurance in radiotherapy. The main motivation is to use this statistical method to optimize the quality assurance processes in the validation of beam models. METHOD: Considering the Varian Eclipse system, eight parameters with several levels were selected: energy, MLC, depth, X, Y1 and Y2 jaw dimensions, wedge and wedge jaw. A Taguchi table was used to define 72 validation tests. Measurements were conducted in water using a CC04 on a TrueBeam STx, a TrueBeam Tx, a Trilogy and a 2300IX accelerator matched by the vendor. Dose was computed using the AAA algorithm. The same raw data was used for all accelerators during the beam modelling. RESULTS: The mean difference between computed and measured doses was 0.1±0.5% for all beams and all accelerators with a maximum difference of 2.4% (under the 3% tolerance level). For all beams, the measured doses were within 0.6% for all accelerators. The energy was found to be an influencing parameter but the deviations observed were smaller than 1% and not considered clinically significant. CONCLUSION: Designs of experiment can help define the optimal measurement set to validate a beam model. The proposed method can be used to identify the prognostic factors of dose accuracy. The beam models were validated for the 4 accelerators which were found dosimetrically equivalent even though the accelerator characteristics differ.

Construction of an extended library of adult male 3D models: rationale and results.

In order to best cover the possible extent of heights and weights of male adults the construction of 25 whole body 3D models has been undertaken. Such a library is thought to be useful to specify the uncertainties and relevance of dosimetry calculations carried out with models representing individuals of average body heights and weights. Representative 3D models of Caucasian body types are selected in a commercial database according to their height and weight, and 3D models of the skeleton and internal organs are designed using another commercial dataset. A review of the literature enabled one to fix volume or mass target values for the skeleton, soft organs, skin and fat content of the selected individuals. The composition of the remainder tissue is fixed so that the weight of the voxel models equals the weight of the selected individuals. After mesh and NURBS modelling, volume adjustment of the selected body shapes and additional voxel-based work, 25 voxel models with 109 identified organs or tissue are obtained. Radiation transport calculations are carried out with some of the developed models to illustrate potential uses. The following points are discussed throughout this paper: justification of the fixed or obtained models' features regarding available and relevant literature data; workflow and strategy for major modelling steps; advantages and drawbacks of the obtained library as compared with other works. The construction hypotheses are explained and justified in detail since future calculation results obtained with this library will depend on them.

[Three cases of IgM monoclonal gammopathy with haemostasis dysfunction]. / Trois cas de gammapathies monoclonales IgM avec anomalies de l'hémostase.

We relate three cases of IgM gammopathy with haemostatic dysfunction in the perioperative period. The acquired von Willebrand syndrome due to IgM gammopathy is rare and sometimes serious. Its different treatments and their efficiency are discussed: desmopressin, intravenous gammaglobulin, chemotherapy and plasmapheresis.

[Peri-operative anticoagulation with danaparoid for a patient with Budd-Chiari syndrome and heparin-induced thrombocytopenia]. / Anticoagulation péri-opératoire par danaparoïde (Orgaran) chez un patient ayant un syndrome de Budd-Chiari et une thrombopénie induite par l'héparine.

We report a case of Budd-Chiari syndrome revealing a polycythemia vera and complicated by heparin-induced thrombocytopenia. A surgical porto-caval shunt was inserted with danaparoid as anticoagulant during the peri-operative period. The doses of danaparoid were as follows: a continuous intravenous infusion of 200 U/h with a target between 0.5 et 0.8 U/ml antifactor Xa activity during the preoperative period, followed by 100 U/h with a target of 0.3 U/ml during the peroperative period; an increase in doses of danaparoid to 150 and 200 U/h with a target above 0.5 U/ml was used during the postoperative period. This case report is a rare situation of hypercoagulable state, in a surgical context, treated with danaparoid.