Determinação do tamanho da fonte de um Acelerador Linear para o algoritmo de cálculo de dose AcurosXB utilizando pequenos campos
DOI:
https://doi.org/10.29384/rbfm.2022.v16.19849001601Keywords:
Spot Size, Algorithm AcurosXB, Linear Accelerator, Dose Calculation Algorithms, Radiochromic Film, Varian TrueBeam STxAbstract
Due to new advances in radiotherapy treatments,such as the intensity modulated techniques,the tools used to describe and represent the linear accelerator have been improved,with a greater concern for dose calculation in small field situations.The AcurosXB algorithm presents interesting results for such problems,however,for the precise calculation it is essential to choose the appropriate parameter of the beam modeling called SpotSize,which is the representation of the primary source that models the created photons Bremsstrahlung created in the target.The study aims to evaluate the influence of SpotSize for the accuracy of small field dose distribution calculation using the AcurosXB algorithm and to find its ideal value.Four models of Spot Size(0.5mm²;1.0 mm², 1,5mm²e1,0x0,5mm²)through the Beam Model tool of TPS were developed,and evaluated in different field sizes and calculation grid size for the Varian TrueBeamSTx LinearAccelerator(MillenniumHD120)using GafchromicEBT3 radiochromic films.The evaluation consists of verifying the absolute dose agreement on the central axis of the beam and the agreement of the planned beam profile with the measured profile through the OmniProI'mRT®Software(IBA).After finding the optimal value, we performed a validation of the ideal model using 10clinical cases of StereotacticRadiosurgery(SRS)of single lesions with maximum dimensions of1.2cc,where Patient-Specific QualityAssurance was performed using the EPIDand the Portal Dosimetry tool.It was found that the 1.0x0.5mm²SpotSize model presented the best results when comparing the irradiated measurements with the planned measurements,which is the recommended model to configure the AcurosXB dose calculation algorithm in small field situations,as in SRS.It was found that the 1.0x0.5mm²SpotSize model presented the best results when comparing the irradiated measurements with the planned measurements.In the clinical cases analyzed,the modeled SpotSize performed at or above the standard SpotSize for gamma analysis with a 1%1mm pass rate and 10%threshold.It is recommended to use the AcurosXB algorithm model with the SpotSize of 1.0x0.5mm²for the calculation of dose distribution in small field situations,as in SRS.
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