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Showing 3 results for Penumbra
W. Parwaie, M. Yarahmadi, H.a. Nedaie, M.h. Zahmatkesh, A.h. Barati, M. Afkhami,
Volume 14, Issue 1 (1-2016)
Abstract
Background: Accurate small radiation field dosimetry is essential in modern radiotherapy techniques such as stereotactic radiosurgery (SRS) and intensity modulated radiotherapy (IMRT). Precise measurement of dosimetric parameters such as beam profile, percentage depth doses and output factor of these beams are complicated due to the electron disequilibrium and the steep dose gradients. In the present work the MAGIC polymer gel was used for dosimetry of small circular photon beams. The results of MAGIC were compared with EBT2 measurements and Monte Carlo (MC) calculations. Materials and Methods: Experimental measurements were made by mentioned dosimeters in four small field sizes 5, 10, 20 and 30 mm. The BEAMnrc code based on EGSnrc was used for simulation to calculate dosimetric parameters at these small fields. The phantoms were irradiated in a 6 MV photon beam Varian 2100C linear accelerator at SSD=100 cm. gel readout performed by 3 Tesla MRI scanner. Results: The results showed that the Percent depth dose (PDD) values measured and calculated by EBT2 film and MC had maximum local differences 4% and 5% with PDD values measured by MAGIC for field size of 5mm respectively. These differences decreased for larger field sizes. The measurements of output factor and penumbra (80%-20%) and (90%-10%) showed good agreement between the measurements and MC calculation. Conclusion: This study showed that the MAGIC polymer gel based on high resolution MRI images is useful detector for small field dosimetry but its agreement with MC is less than agreement of EBT2 film with MC.
Dr. H. Alipour, K. Hadad, R. Faghihi,
Volume 17, Issue 3 (6-2019)
Abstract
Background: Due to the small size of the beamlets in IMRT (intensity modulated radiotherapy), physical penumbra is one of the important dosimetric parameters and small changes in the penumbra have a notable impact on the results. The physical penumbra width is defined as the lateral distance between two specified isodose curves at a specified depth of phantom. In this study, after demonstrating the inconsistency of conventional physical penumbra definition for non-uniform MLC (multileaf collimator) fields, two new dosimetric parameters proposed that are suitable for MLC fields. Materials and Methods: Physical penumbra evaluation was obtained using IAEA (international atomic energy agency) phase space data for a Varian IX and EGS (electron gamma shower)nrc Monte Carlo code package. These measurements have been performed in water phantom at an SSD of 100 cm and a depth of 5 cm. Results: With conventional definition, physical penumbra width for all MLC setups on right and left sides of isodose curves (parallel to X and Y axes) are not equal. With a novel beam penumbra parametrization, the effect of MLC setup is taken into consideration. Conclusion: The conventional definition of physical penumbra for non-uniform MLC setups is not comprehensive. For such cases, surface penumbra and uniformity index parameters are demonstrated to be more suitable and indicative of the field non-uniformity. It is also shown that for an idle treatment planning system, the uniformity index approaches unity.
S. Hassn, N.a. Deiab, Phd., A.h. Aly,
Volume 18, Issue 1 (1-2020)
Abstract
Background and Objectives: To show whether the 2D-array scanning system can be used as a substitute for the MP3-water phantom, we have used a comparison of beam profiles and the percentage depth doses for both electron beams and the photons, also we have confirmed the validation of the results by CMS XiO treatment planning system. Methods: Beam data was obtained for MP3-water phantom and 2D-array scanning system for 6 MV and 15 MV photon beam; and 4, 6, 8, 10, 12 and 15 MeV electron beams generated from ONCOR Digital Medical Linear accelerator for (2×2cm2, 3×3cm2, 5×5cm2,10×10cm2,15×15cm2and 20×20cm2) at 10cm depth. CMS XiO treatment planning system was utilized for validation of the obtained data. Results: doses distribution for the two studied systems is compared with uncertainties within the recommended limits. It is found that there's no vital variation in flatness and symmetry obtained from the 2D-Array as compared to the quality MB3-Water Phantom Flatness and symmetry obtained is well at intervals the limit of ±3%. Conclusion: it is concluded that the 2D-Array-729 is used for the routine measuring of the photon beam profiles as alternative to water phantom.
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