Marinelli beaker systems are used to monitor the activity of radioactive samples. These systems are usually calibrated with water solutions and the determination of the activity in gases requires ...correction coefficients accounting for the different mass-thickness of the sample. For beta+ radionuclides the different distribution of the positrons annihilation points should be also considered. In this work a Monte Carlo simulation based on Geant4 is used to compute correction coefficients for the measurement of the activity of air samples.
•A GEANT4 simulation is developed for the calibration of an air monitoring system.•Correction for both gamma and beta+ emitters are obtained.•Simulation results are compared with analytical self-attenuation correction factors.•The estimated accuracy of the Monte Carlo technique is within 2%.
Introduction Focused ultrasound are recently introduced as alternative therapy for pain palliation caused by bone metastases. The heat absorption and propagation in the soft tissues and in the bones ...strongly depends on the correct focalization of the ultrasonic beam through the interfaces. The real-time thermal map provided by the MRI gives to the interventional radiologist the feedback for the online treatment planning. Purpose The present work is focused on the verification of planning therapy system of a MRgFUs system giving a verification of the propagation and the accumulation of the temperature in bones in particular for the pelvic bone. Materials and methods In this work it has been studied the Philips Sonalleve HIFU installed on Ingenia 3T. The thermal maps has been studied on a multi-interface phantom with albumin-agarose gel volumetric detector. The planned volume ablation temperature has been compared with the T2 imaging modification on the phantom. A dedicated software has been developed for the extraction of the thermal image maps from the system and for the evaluation of the cumulative thermal dose. A first approach has been proposed for the evaluation of the plan in term of DVH (dose/volume histogram). Results High impedance interfaces create local depositions of energy along the sonicated surfaces. The plan cumulative dose verification gives constraints to the physicians on sonication cells positioning. Conclusion The MRgFUs feedback planning gives partial information of the heat deposition. The bone phantom is used to evaluate the real cells volume. The de-focalization created by bones demonstrate the needs of preplanning system dedicated to bones treatments.
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