Purpose/objective: The objective of this study was to verify the accuracy of treatment plans of stereotactic body radiation therapy (SBRT) and to verify the feasibility of the use of Monte Carlo (MC) as quality control (QC) on a daily basis. Material/methods: Using EGSnrc, a MC model of Agility T linear accelerator was created. Various measurements (Percentage depth dose (PDD), Profiles and Output factors) were done for different fields sizes from 1x1 up to 40x40 (cm(2)). An iterative model optimization was performed to achieve adequate parameters of MC simulation. 40 SBRT patient's dosimetry plans were calculated by Monaco T 3.1.1. CT images, RT-STRUCT and RT-PLAN files from Monaco T being used as input for Moderato MC code. Finally, dose volume histogram (DVH) and paired t-tests for each contour were used for dosimetry comparison of the Monaco T and MC. Results: Validation of MC model was successful, as <2% difference comparing to measurements for all field's sizes. The main energy of electron source incident on the target was 5.8 MeV, and the full width at half maximum (FWHM) of Gaussian electron source were 0.09 and 0.2 (cm) in X and Y directions, respectively. For 40 treatment plan comparisons, the minimum absolute difference of mean dose of planning treatment planning (PTV) was 0.1% while the maximum was 6.3%. The minimum absolute difference of Max dose of PTV was 0.2% while the maximum was 8.1%. Conclusion: SBRT treatment plans of Monaco agreed with MC results. It possible to use MC for treatment plans verifications as independent QC tool.

Purpose. - Shielding disks play an important role in intraoperative electron radiation therapy, and different designs are currently used in clinical practice. This paper investigates the dosimetric impact of the shielding disk used during intraoperative electron radiation therapy (IOERT). Materials and Methods. - This paper focuses on the study of four shielding disks types that have been used in our clinic: Aluminum (Al)/Lead (Pb), PMMA/Copper(Cu)/PMMA, Aluminum (Al)/Copper (Cu) and Aluminum (Al)/Steel with their specific thicknesses. The theoretical study was conducted with the EGSnrc Monte Carlo (MC) code. On the other hand, the measurements were carried out with gafchromic films for the four shielding disks for the same setup inside the water phantom. Finally, a comparison of the simulated and measured PDD curves was performed for the four material combinations. Results. - MC simulation and gafchromic measurements illustrated that dose values under the four shielding disks types were close to 0, whereas the backscattering enhancement of the disks were 103% with Al/Pb shielding disk, 102% with Al/Steel shielding disk, 102% with Al/Cu shielding disk, 95% with PMMA/Cu/PMMA shielding disk. The PDDs values of the gafchromic films in front of the disks were: 107%, 105%, 104%, and 94% for the Al/Pb, Al/Steel, Al/Cu, and PMMA/Cu/PMMA disks respectively. Conclusions. - The dose values above and under the shielding disks were acceptable for the four studied shielding types. Demonstrated it is possible to use any of them clinically, while the best shielding disk was the Al/Pb since it has minimum thickness and a small backscatter enhancement. (C) 2020 Societe francaise de radiotherapie oncologique (SFRO). Published by Elsevier Masson SAS. All rights reserved.

As expected, our results show that with decreasing detector size, the measured penumbra width and therefore the distance to the point of inflection decreases [2].Considering all energies, the mean time duration for linac output constancy daily measurement using EPID and IC was respectively 16 and 30 minutes.The mean time duration for beam parameters measurement using EPID and IC was respectively 14 and 200 minutes. ConclusionThe use of automatic EPID based beam QA dramatically decreases the time dedicated to QA, eliminates manual steps in the process, reducing human errors, improving efficiency, robustness and productivity for radiotherapy providers with a significant decrease in waiting time for patients.In our institution we have chosen to use daily EPID QA to verify output constancy and beam uniformity without any modification on quality or tolerances of our QA process.

PurposeThis paper studies the feasibility of using Monte Carlo (MC) for treatment planning of intraoperative electron radiation therapy (IOERT) procedure to get 3D dose by using patient’s CT images.MethodsThe IOERT treatment planning was performed using the following successive steps:I) The Mobetron 1000® machine was modelled with the EGSnrc MC codes. II) The MC model was validated with measurements of percentage depth doses and profiles for three energies (12, 9, 6) MeV. III) CT images were imported as DICOM files. IV) Contouring of the planning target volume (PTV) and the organs at risk was done by the radiation oncologist. V) The medical physicist with the radiation oncologist, had chosen the same parameters of IOERT procedures like energy, applicator (type, size) and using or not bolus. VI) Finally, dose calculation and analysis of 3D maps was carried out.ResultsThe tuning process of the MC model provides good results, as the maximum value of the root mean square deviation (RMSD) was less than 3% between the MC simulated PDDs and the measured PDDs. The contouring and dose analysis review were easy to conduct for the classical treatment planning system. The radiation oncologist had many tools for dose analysis such as DVH and color wash for all the slides. Summation of the 3D dose of IOERT with other radiotherapy plans is possible and helpful for total dose estimation. Archiving and documentation is as good as treatment planning system (TPS).ConclusionsThe method displayed in this paper provides a step forward for IOERT Dosimetry and allows to obtain accurate dosimetry of treated volumes.

PURPOSE:In IOERT breast treatments, a shielding disk is frequently used to protect the underlying healthy structures. The disk is usually composed of two materials, a low-Z material intended to be oriented towards the beam and a high-Z material. As tissues are repositioned around the shield before treatment, the disk is no longer visible and its correct alignment with respect to the beam is guaranteed. This paper studies the dosimetric characteristics of four possible clinical positioning scenarios of the shielding disk. A new alignment method for the shielding disk in the beam is introduced. Finally, it suggests a new design for the shielding disk.METHODS:As the first step, the IOERT machine "Mobetron 1000" was modeled by using Monte Carlo simulation, tuning the MC model until an excellent match with the measured PDDs and profiles was achieved. Four possible shielding disk positioning scenarios were considered, determining the dosimetric impact. Furthermore, in our center, to prevent beam misalignment, we have developed a shielding disk equipped with guiding rods. Having ascertained a correct alignment between the disk and the beam, we can propose a new internal design of the shielding disk that can improve the dose distribution with a better coverage of the treated area.RESULTS:All MC simulations were performed with a 12 MeV beam, the maximum energy of Mobetron 1000 and a 5.5 cm diameter flat tip applicator, this applicator being the most clinically used. The simulations were compared with measurements performed in a water phantom and showed good results within 2.2% of root mean square difference (RMSD). The misplacement positions of the shielding disk have dosimetric impacts in the treatment volume and a small translation could have a significant influence on healthy tissues. The D-scenario is the worst which could happens when the shielding disk is flipped upside down, giving up to 144% dose instead of 90% at the surface of the Pb/Al shielding disk. A new shielding design used, together with our alignment tool, is able to give a more homogeneous dose in the target area.CONCLUSIONS:The accuracy of shielding disk position can still be problematic in IOERT dosimetry. Any method that can ascertain the good alignment between the shielding disk and the beam is beneficial for the dose distribution and is a prerequisite for an optimized shield internal design that could improve the coverage of the treated area and the protection of healthy tissues.

dict the delivered absorbed dose distribution, allowing comparison with the TPS.EPID images were taken during 6MV treatment delivery, with a dose rate of 600 MU/min, from aSi1000 EPID (Varian).Mounted with Exact-arm on a Clinac 23iX equipped with a multi-leaf collimator (120 leaves).The EPID were acquired using the half-resolution mode.2D plane images were calculated in Eclipse TM at the maximum depth dose in a water phantom.Results.Learning was performed using 11 input/output datasets from IMRT treatments.All of the used datasets (both EPID inputs and absorbed dose distribution outputs) consisted of 384 Â 512 pixels.Learning can be time consuming but once the ANN has been fixed, its use during the recognition phase will be instantaneous.The gamma index, c, was used to evaluate the difference between the ANN calculated and planned distributions.c gives the number of pixels (as a percentage) that respect a given objective.c (2% , 2 mm) for Head and Neck cancers was found to be 99.7%, highlighting the ANN capability to predict the absorbed dose distribution based on EPIDs.Conclusions.It was shown that patient-specific quality assurance of IMRT based on EPID can be performed with neural networks algorithms.Next work would be extending algorithms for in vivo dosimetry purpose.