For intensity‐modulated radiation therapy, evaluation of the measured dose against the treatment planning calculated dose is essential in the context of patient‐specific quality assurance. The complexity of volumetric arc radiotherapy delivery attributed to its dynamic and synchronization nature require new methods and potentially new tools for the quality assurance of such techniques. In the present study, we evaluated and compared the dosimetric performance of EDR2 film and three other commercially available quality assurance devices: IBA I'MatriXX array, PTW Seven29 array and the Delta 4 array. The evaluation of these dosimetric systems was performed for RapidArc and IMRT deliveries using a Varian NovalisTX linear accelerator. The plans were generated using the Varian Eclipse treatment planning system. Our results showed that all four QA techniques yield equivalent results. All patient QAs passed our institutional clinical criteria of gamma index based on a 3% dose difference and 3 mm distance to agreement. In addition, the Bland‐Altman analysis was performed which showed that all the calculated gamma values of all three QA devices were within 5% from those of the film. The results showed that the four QA systems used in this patient‐specific IMRT QA analysis are equivalent. We concluded that the dosimetric systems under investigation can be used interchangeably for routine patient specific QA.PACS numbers: 87.55.Qr, 87.56.Fc

Intensity‐modulated radiotherapy treatment demands stringent quality assurance and accurate dose determination for delivery of highly conformal dose to the patients. Generally 3D dose distributions obtained from a treatment planning system have to be verified by dosimetric methods. Mainly, a comparison of two‐dimensional calculated and measured data in several coplanar planes is performed. In principle, there are many possibilities to measure two‐dimensional dose distributions such as films, flat‐panel electronic portal imaging devices (EPID), ion chambers and ionization chamber arrays, and radiographic and radiochromic films. The flat‐panel EPIDs show a good resolution and offer a possibility for real‐time measurements: however to convert the signal into dose, a separate commercial algorithm is required. The 2D ion chamber array system offers the real‐time measurements. In this study, dosimetric characteristics of 2D ion chamber array matrix were analyzed for verification of radiotherapy treatments. The dose linearity and dose rate effect of the I'matriXX device was studied using 6 MV, 18 MV photons and 12 MeV electrons. The output factor was estimated using I'matriXX device and compared with ion chamber measurements. The ion chamber array system was found to be linear in the dose range of 2–500 cGy and the response of the detector was found to be independent of dose rate between 100 MU/min to 600 MU/min. The estimated relative output factor with I'matriXX was found to match very well with the ion chamber measurements. To check the final dose delivered during IMRT planning, dose distribution patterns such as field‐in‐field, pyramidal, and chair tests were generated with the treatment planning system (TPS) and the same was executed in the accelerator and measured with the I'matriXX device. The dose distribution pattern measured by the matrix device for field‐in‐field, pyramidal, and chair test were found to be in good agreement with the calculated dose distribution by TPS both for 6 and 18 MV photons (γ ≤ 1: 96%, criteria 3%, 3 mm). Two 7‐field IMRT plans (one prostate, one head and neck) dose distribution patterns were also measured with I'matriXX device and compared with film dosimetry. The measurements and evaluation proves that I'matriXX can be used for quantifying absolute dose. Moreover, using I'matriXX as absolute dosimeter in IMRT field verification, avoids the time‐consuming procedure of making ionometric measurement for absolute dose estimation and film for dose distribution verification. The I'matriXX can also used for routine quality assurance checks like flatness, symmetry, field width, and penumbra of the linear accelerator beam.PACS number: 87.55.ne and 87.56.Fc

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The complexity of VMAT delivery requires new methods and potentially new tools for the commissioning of these systems. It appears that great consideration is needed for quality assurance (QA) of these treatments since there are limited devices that are dedicated to the QA of rotational delivery. In this present study, we have evaluated the consistency and reproducibility of one prostate and one lung VMAT plans for 31 consecutive days using three different approaches: 1) MLC DynaLog files, 2) in vivo measurements using the multiwire ionization chamber DAVID, and 3) using PTWseven29 2D ARRAY with the OCTAVIUS phantom at our Varian Clinac linear accelerator. Overall, the three methods of testing the reproducibility and consistency of the VMAT delivery were in agreement with each other. All methods showed minimal daily deviations that contributed to clinically insignificant dose variations from day to day. Based on our results, we conclude that the VMAT delivery using a Varian 2100CD linear accelerator equipped with 120 MLC is highly reproducible.PACS numbers: 87.55.Qr and 87.56.Fc

The increase in surface dose with field size for both photon energies is due to the electron scattering from the intervening materials. The use of wedge filters absorbs low-energy scattered electrons significantly and hence, the relative surface dose (RSD) is always less than unity. The increase in dose enhancement percentage with graphite compared to perspex supporting assembly indicates that the electron backscatter is proportional to the atomic number of the medium.