RESUMO
Purpose: To validate a locally fabricated phantom of Imatrixx-2D Array by comparing its results with ArcCheck phantom and comparing portal dosimetry measurements with the two phantom studies. Materials and Methods: Electronic Portal Imaging Devices and Epiqa software were used for portal dosimetry. An Imatrixx-2D array with a locally fabricated phantom and ArcCheck cylindrical phantom were used for phantom studies. Eclipse-TPS with RapidArc treatment planning and portal dose prediction software was used for planar dose calculations. Three verification plans were created for each of the 15 patient plans of various sites, making a total of 45 plans to be delivered on 3 QA systems as above. Fifteen plans each with 2 arcs were delivered on the EPIDs of the Linacs, on Imatrixx-2D array phantom and on ArcCheck cylindrical phantom respectively. The planar dose matrices were analysed using global Gamma Index criteria of 3mm DTA and 3% dose difference. Results: The maximum deviations of percentage in dose points, in which γ>1, are 1.94, 1.89 and 1.5 in Imatrixx phantom, ArcCheck phantom and Portal dosimetry, respectively. Similarly, the mean deviations and SD values are less in portal dosimetry than that of phantom studies. The smaller deviations in portal dosimetry are attributed to closely embedded chambers in the EPID compared to the distance between the detectors placed in the phantom measurements. Conclusion: After carrying out the comparison of results, the locally fabricated phantom has been validated and accepted for the dosimetric studies. The conclusion is that all the three dosimetric QA systems are suitable for the patient-specific QA of RapidArc treatments.
RESUMO
DQA, a patient specific quality assurance in tomotherapy, is usually performed using an ion chamber and a film. The result of DQA is analysed with the treatment planning system called Tomo Planning Station (TomoPS). The two-dimensional dose distribution of film measurement is compared with the dose distribution calculated by TomoPS using the gamma-index analysis. In gamma-index analysis, the criteria such as 3%/3 mm is used and we verify that whether the rate of number of points which pass the criteria (pass rate) is within tolerance. TomoPS does not provide any quantitative information regarding the pass rate. In this work, a method to get the pass rate of the gamma-index analysis was suggested and a software PassRT which calculates the pass rate was developed. The results of patient specific QA of the intensity modulated radiation therapy measured with I'mRT MatriXX (IBA Dosimetry, Germany) and DQA of tomotherapy measured with film were used to verify the proposed method. The pass rate was calculated using PassRT and compared with the pass rate calculated by OmniPro I'mRT (IBA Dosimetry, Germany). The average difference between the two pass rates was 0.00% for the MatriXX measurement. The standard deviation and the maximum difference were 0.02% and 0.02%, respectively. For the film measurement, average difference, standard deviation and maximum difference were 0.00%, 0.02% and 0.02%, respectively. For regions of interest smaller than 24.3x16.6 cm2 the proposed method can be used to calculate the pass rate of the gamma index analysis to one decimal place and will be helpful for the more accurate DQA in tomotherapy.