Journal of Medical Physics
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Year : 2015  |  Volume : 40  |  Issue : 3  |  Page : 129-135

Determination of dosimetric leaf gap using amorphous silicon electronic portal imaging device and its influence on intensity modulated radiotherapy dose delivery

Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
S Timothy Peace Balasingh
Department of Radiotherapy, Christian Medical College, Vellore - 632 004, Tamil Nadu
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Source of Support: Nil., Conflict of Interest: There are no conflicts of interest.

DOI: 10.4103/0971-6203.165072

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As complex treatment techniques such as intensity modulated radiotherapy (IMRT) entail the modeling of rounded leaf-end transmission in the treatment planning system, it is important to accurately determine the dosimetric leaf gap (DLG) value for a precise calculation of dose. The advancements in the application of the electronic portal imaging device (EPID) in quality assurance (QA) and dosimetry have facilitated the determination of DLG in this study. The DLG measurements were performed using both the ionization chamber (DLGion) and EPID (DLGEPID) for sweeping gap fields of different widths. The DLGion values were found to be 1.133 mm and 1.120 mm for perpendicular and parallel orientations of the 0.125 cm3 ionization chamber, while the corresponding DLGEPID values were 0.843 mm and 0.819 mm, respectively. It was found that the DLG was independent of volume and orientation of the ionization chamber, depth, source to surface distance (SSD), and the rate of dose delivery. Since the patient-specific QA tests showed comparable results between the IMRT plans based on the DLGEPID and DLGion, it is concluded that the EPID can be a suitable alternative in the determination of DLG.

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