Publications by authors named "Stefano Riga"

3 Publications

  • Page 1 of 1

MRI only in a patient with prostate cancer with bilateral metal hip prostheses: case study.

Tumori 2021 Feb 25:300891621997549. Epub 2021 Feb 25.

Medical Physics Department, ASST Grande Ospedale Metropolitano Niguarda, Milano, Italy.

Objective: To outline a practical method of performing prostate cancer radiotherapy in patients with bilateral metal hip prostheses with the standard resources available in a modern general hospital. The proposed workflow is based exclusively on magnetic resonance imaging (MRI) to avoid computed tomography (CT) artifacts.

Case Description: This study concerns a 73-year-old man with bilateral hip prostheses with an elevated risk prostate cancer. Magnetic resonance images with assigned electron densities were used for planning purposes, generating a synthetic CT (sCT). Imaging acquisition was performed with an optimized Dixon sequence on a 1.5T MRI scanner. The images were contoured by autosegmentation software, based on an MRI database of 20 patients. The sCT was generated assigning averaged electron densities to each contour. Two volumetric modulated arc therapy plans, a complete arc and a partial one, where the beam entrances through the prostheses were avoided for about 50° on both sides, were compared. The feasibility of matching daily cone beam CT (CBCT) with MRI reference images was also tested by visual evaluations of different radiation oncologists.

Conclusions: The use of magnetic resonance images improved accuracy in targets and organs at risk (OARs) contouring. The complete arc plan was chosen because of 10% lower mean and maximum doses to prostheses with the same planning target volume coverage and OAR sparing. The image quality of the match between performed CBCTs and MRI was considered acceptable. The proposed method seems promising to improve radiotherapy treatments for this complex category of patients.
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February 2021

Validation of a dose tracking software for skin dose map calculation in interventional radiology.

Phys Med 2020 Apr 3;72:122-132. Epub 2020 Apr 3.

Medical Physics Department, ASST Grande Ospedale Metropolitano Niguarda, Piazza Ospedale Maggiore 3, 20162 Milano, Italy.

Purpose: Validate the skin dose software within the radiation dose index monitoring system NEXO[DOSE]® (Bracco Injeneering S.A., Lausanne, Switzerland). It provides the skin dose distribution in interventional radiology (IR) procedures.

Methods: To determine the skin dose distribution and the Peak Skin Dose (PSD) in IR procedures, the software uses exposure and geometrical parameters taken from the radiation dose structured report and additional information specific to each angiographic system. To test the accuracy of the software, GafChromic® XR-RV3 films, wrapped under a cylindrical PMMA phantom, were irradiated with different setups. Calculations and films results are compared in terms of absolute dose and geometric accuracy, using two angiographic systems (Philips Integris Allura FD20, Siemens AXIOM-ArtisZeego).

Results: Calculated and film measured PSD values agree with an average difference of 7% ± 5%. The discrepancies in dose evaluation increase up to 33% in lower dose regions, because the algorithm does not consider the out-of-field scatter contribution of the neighboring fields, which is more significant in these areas. Regarding the geometric accuracy, the differences between the simulated dose spatial distributions and the measured ones are<3 mm (4%) in simple tests and 5 mm (5%) in setups closer to clinical practice. Moreover, similar results are obtained for the two studied angiographic system vendors.

Conclusions: NEXO[DOSE]® provides an accurate skin dose distribution and PSD estimate. It will allow faster and more accurate monitoring of patient follow-up in the future.
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April 2020

Production of Ga-68 with a General Electric PETtrace cyclotron by liquid target.

Phys Med 2018 Nov 25;55:116-126. Epub 2018 Oct 25.

Medical Physics Department, University Hospital, S. Orsola-Malpighi, Bologna, Italy.

Purpose: In recent years the use of Ga (t = 67.84 min, β: 88.88%) for the labelling of different PET radiopharmaceuticals has significantly increased. This work aims to evaluate the feasibility of the production of Ga via the Zn(p,n)Ga reaction by proton irradiation of an enriched zinc solution, using a biomedical cyclotron, in order to satisfy its increasing demand.

Methods: Irradiations of 1.7 Msolution of Zn(NO) in 0.2 N HNO were conducted with a GE PETtrace cyclotron using a slightly modified version of the liquid target used for the production of fluorine-18. The proton beam energy was degraded to 12 MeV, in order to minimize the production of Ga through theZn(p,2n)Ga reaction. The product's activity was measured using a calibrated activity meter and a High Purity Germanium gamma-ray detector.

Results: The saturation yield ofGa amounts to (330 ± 20) MBq/µA, corresponding to a produced activity ofGa at the EOB of (4.3 ± 0.3) GBq in a typical production run at 46 µA for 32 min. The radionuclidic purity of theGa in the final product, after the separation, is within the limits of the European Pharmacopoeia (>99.9%) up to 3 h after the EOB. Radiochemical separation up to a yield not lower than 75% was obtained using an automated purification module. The enriched material recovery efficiency resulted higher than 80-90%.

Conclusions: In summary, this approach provides clinically relevant amounts ofGa by cyclotron irradiation of a liquid target, as a competitive alternative to the current production through theGe/Ga generators.
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November 2018