Small field size dose-profile measurements using MAGIC- f polymer gel dosimeter and EBT3 film dosimeter

Document Type: Conference Proceedings

Authors

1 Medical Physics and Biomedical Engineering Department, Shahid Beheshti University of Medical sciences, Tehran, Iran

2 Radio-Oncology Department, ShohadaeTajrish hospital, ShahidBeheshti University of Medical sciences, Tehran, Iran

Abstract

Introduction: In radiotherapy, treatment planning methods are evaluating and transforming every day, so precision in calculation and determination of dose delivery process is performing more important role in radiotherapy than past. In modern radiotherapy treatments, deramatically increase of small fields utilization, causes the polymeric gels has known as the most reliable dosimeter for this kind of fields. Polymer gel dosimeters contain radiation sensitive materials that are irradiated as a function of polymerized absorbed dose, and the spatial information of the radiation dose distribution is extracted by imaging the irradiated gel. In this study, the polymeric system dosimeters performance MAGIC-f gel which obtained from the MRI imaging method, were compared with the EBT3 film dosimeter.
Materials and Methods: A polymer gel type called MAGIC-f was applied in this study is as the same as type of polymer used in Fernandes et al study. After preparing the required gel and pouring it into phantoms and calibration tubes, they were irradiated with 6 MV photon beam, then dose distribution R2 maps were obtained by (3T MRI) taking MR images of them. Dicom images and necessary parameters were extracted by MATLAB and imagej software. The dose-profile was measured for three small field size (5,10,15 mm diameters) by using polymer gel compared with results of the EBT3 film dosimetry.
Results: With Comparing the obtained results of two dosimeters, the maximum difference between the measured profiles was observed in penumbra areas (out of range). In these regions, the penumbra which measured by MAGIC-f was almost 1 mm larger than the measured width of penumbra by EBT3 film dosimeter. The maximum variation was seen in the flat area (isodose 90%) of the 0.5×0.5 cm2 dose profile curve was 4.68%. In the 1×1 and 1.5×1.5 cm2 fields, the greatest difference in the flat area of dose profile curve was 3.04% and 4.48%.
Conclusion: In summarize MAGIC-f gel is more convenient and stable dosimeter than film for small fields studies. Moreover, it has a substantial potential for utilization as a 3D dosimeter in clinical applications of radiation therapy. Differences in the cross-sectional dose profile curves between polymer gel dosimeters (MAGIC-f) and film EBT3 can explain by various factors, such as way of preparing gel, materials quality which used in gel composition, and the quality of the imaging system.

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