Purpose: Evaluation and comparison of 2D electronic systems versus film/ion chamber based dosimetry for IMRT QA using MapCHECK and MatriXX. Method and Materials: All IMRT plans were generated with Eclipse/Helios 7.3.10 treatment planning software (Varian). Treatments were delivered on a Varian 21EX linear accelerator (6MV) with 120 leaf Millenium MLC for delivery of sliding window IMRT. The film measurements were first compared to the Eclipse dose plane. Secondly, the electronic measurements were compared to the Eclipse dose plane. Thirdly, the film measurements were compared to the electronic measurements. The film, Eclipse dose plane and MatriXX (Scanditronix) were analyzed using the OmniPro IMRT software (Scanditronix). The film, Eclipse dose plane and MapCHECK (SunNuclear) were analyzed using the MapCHECK software. Analysis was based on distance to agreement (DTA), Gamma, profile comparisons, measured dose (relative/absolute) and visual comparison. Results: Film and ion chamber comparisons were in good agreement as well as comparisons between electronic and ion chamber measurements. However, in some instances, electronic system measurements did not agree with film due to MLC leaf failure. Advantages and disadvantages of MatriXX and MapCheck for IMRT QA as well as specific MLC leaf failure instances will be discussed further. Conclusion: With many clinics implementing electronic IMRT QA devices, a careful understanding of the limitations of the MLC system and the electronic IMRT QA device is needed. We are investigating the resolution capabilities of each QA system. The MLC failure was caught before treatment began. A major disadvantage in implementing 2D electronic systems for IMRT QA is the limited resolution, resulting in limited sensitivity to MLC failures. Primary advantages of 2D electronic systems include: 1) time, 2) efficiency, 3) ease of use, and 4) overall simplification of IMRT QA.
The intensity and quality of scattered radiations incident on the eye during mantle-field therapy were measured for 4-MV x rays. Beam-shaping appliances were found to introduce considerable soft scatter. Eye shields reduce radiation exposure from the anterior field approximately threefold.
Purpose: Comparison of 2D electronic array systems with film for IMRT QA. Method and Materials: Two electronic array systems, MapCHECK (SunNuclear) and MatriXX (Scanditronix), were evaluated and compared with EDR2, XV, and Gafchromic EBT film. Patient evaluations included two H&N, two prostate, and two “problem” patients. Planning was done with Eclipse/Helios 7.3.10 treatment planning software (Varian) (TPS). All measurements were taken at a depth of 10 cm on a Varian 21EX linear accelerator (6MV). All measurements were compared with the TPS and film. Gamma analysis, isodose distributions, and profiles were analyzed for each comparison. Results: Film was found to have absolute dose values 20 – 30% higher than MapCHECK and MatriXX. EDR2 film measurements demonstrated smaller penumbra than either the plan or the 2D systems. Both 2D (electronic) systems demonstrated lower resolution and sensitivity issues than film demonstrated. Selection of the region of interest, detector position, and normalization methods also affected final outcome. Conclusion: The EDR2 and EBT film dose ranges do not appear optimal for individual field analysis. Film vs MatriXX agree (point to point) better with each other than with plan. MapCHECK's high density option requiring on extra acquisition (3.5mm offset) was found to be slightly useful and confirmed higher resolution advantages. Recommendations for IMRT QA is to have two methods at each facility; a standard method (such as 2D array) and a more detailed backup method (such as film). 2D arrays can provide a complete QA package with resolution limitations. Film analysis for MapCHECK is awkward at best with GafChromic analysis for both MapCHECK and MatriXX being better but demonstrated difficulties in user friendliness and final values. The MatriXX film analysis was preferred.
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