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Soriani A.,Laboratory of Medical Physics | Felici G.,Sordina S.p.A Technical Division | Fantini M.,Sordina S.p.A Technical Division | Paolucci M.,ASL N.3 | And 4 more authors.
Medical Physics | Year: 2010

Purpose: The aim of this study is to investigate radioprotection issues that must be addressed when dedicated accelerators for intraoperative radiotherapy (IORT) are used in operating rooms. Recently, a new version of a mobile IORT accelerator (LIAC Sordina SpA, Italy) with 12 MeV electron beam has been implemented. This energy is necessary in some specific pathology treatments to allow a better coverage of thick lesions. At an electron energy of 10 MeV, leakage and scattered x-ray radiation (stray radiation) coming from the accelerator device and patient must be considered. If the energy is greater than 10 MeV, the x-ray component will increase; however, the most meaningful change should be the addition of neutron background. Therefore, radiation exposure of personnel during the IORT procedure needs to be carefully evaluated. Methods: In this study, stray x-ray radiation was measured and characterized in a series of spherical projections by means of an ion chamber survey meter. To simulate the patient during all measurements, a polymethylmethacrylate (PMMA) slab phantom with volume 30×30×15 cm3 and density 1.19 g/ cm3 was used. The PMMA phantom was placed along the central axis of the beam in order to absorb the electron beams and the tenth value layer (TVL) and half value layer (HVL) of scattered radiation (at 0°, 90°, and 180° scattering angles) were also measured at 1 m of distance from the phantom center. Neutron measurements were performed using passive bubble dosimeters and a neutron probe, specially designed to evaluate ambient dose equivalent H (10). Results: The x-ray equivalent dose measured at 1 m along the beam axis at 12 MeV was 260 μSv/Gy. The value measured at 1 m at 90° scattering angle was 25 μSv/Gy. The HVL and TVL values were 1.1 and 3.5 cm of lead at 0°, and 0.4 and 1 cm at 90°, respectively. The highest equivalent dose of fast neutrons was found to be at the surface of the phantom on the central beam axis (2.9±0.6 μSv/Gy), while a lower value was observed below the phantom (1.6±0.3 μSv/Gy). The neutron dose equivalent at 90° scattering angle and on the floor plane on the beam axis below the beam stopper was negligible. Conclusions: Our data confirm that neutron exposure levels around the new dedicated IORT accelerator are very low. Mobile shielding panels can be used to reduce x-ray levels to below regulatory levels without necessarily providing permanent shielding in the operating room. © 2010 American Association of Physicists in Medicine.

Pasciuti K.,Laboratory of Medical Physics | Iaccarino G.,Laboratory of Medical Physics | Strigari L.,Laboratory of Medical Physics | Malatesta T.,S. Giovanni Calibita | And 5 more authors.
Medical Dosimetry | Year: 2011

The aim of this study was to evaluate the differences in accuracy of dose calculation between 3 commonly used algorithms, the Pencil Beam algorithm (PB), the Anisotropic Analytical Algorithm (AAA), and the Collapsed Cone Convolution Superposition (CCCS) for intensity-modulated radiation therapy (IMRT). The 2D dose distributions obtained with the 3 algorithms were compared on each CT slice pixel by pixel, using the MATLAB code (The MathWorks, Natick, MA) and the agreement was assessed with the γ function. The effect of the differences on dose-volume histograms (DVHs), tumor control, and normal tissue complication probability (TCP and NTCP) were also evaluated, and its significance was quantified by using a nonparametric test. In general PB generates regions of over-dosage both in the lung and in the tumor area. These differences are not always in DVH of the lung, although the Wilcoxon test indicated significant differences in 2 of 4 patients. Disagreement in the lung region was also found when the Γ analysis was performed. The effect on TCP is less important than for NTCP because of the slope of the curve at the level of the dose of interest. The effect of dose calculation inaccuracy is patient-dependent and strongly related to beam geometry and to the localization of the tumor. When multiple intensity-modulated beams are used, the effect of the presence of the heterogeneity on dose distribution may not always be easily predictable. © 2011 American Association of Medical Dosimetrists.

Iaccarino G.,Laboratory of Medical Physics | Strigari L.,Laboratory of Medical Physics | D'Andrea M.,Laboratory of Medical Physics | Bellesi L.,Laboratory of Medical Physics | And 4 more authors.
Physics in Medicine and Biology | Year: 2011

The aim of this study was to investigate the dosimetric characteristics of the electron beams generated by the light intraoperative accelerator, Liac® (SORDINA, Italy), using Monte Carlo (MC) calculations. Moreover we investigated the possibility of characterizing the Liac® dosimetry with a minimal set of dosimetric data. In fact accelerator commissioning requires measurements of both percentage depth doses (PDDs) and off-axis profiles for all the possible combinations of energy, applicator diameter and bevelled angle. The Liac® geometry and water phantom were simulated in a typical measurement setup, using the MC code EGSnrc/BEAMnrc. A simulated annealing optimization algorithm was used in order to find the optimal non-monoenergetic spectrum of the initial electron beam that minimizes the differences between calculated and measured PDDs. We have concluded that, for each investigated nominal energy beam, only the PDDs of applicators with diameters of 30, 70 and 100 mm and the PDD without an applicator were needed to find the optimal spectra. Finally, the output factors of the entire set of applicator diameters/bevelled angles were calculated. The differences between calculated and experimental output factors were better than 2%, with the exception of the smallest applicator which gave differences between 3% and 4% for all energies. The code turned out to be useful for checking the experimental data from various Liac® beams and will be the basis for developing a tool based on MC simulation to support the medical physicist in the commissioning phase. © 2011 Institute of Physics and Engineering in Medicine.

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