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Penumbral Dose Characteristics of Physical and Virtual Wedge Profiles

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DOI: 10.4236/ijmpcero.2017.62020    829 Downloads   1,338 Views Citations

ABSTRACT

Purpose: Both physical and virtual wedges are used in radiotherapy to get uniform and desired dose distribution in clinical setting. All linear accelerators of different venders have computer controlled dynamic wedges called virtual wedge filters. Penumbra is one of the important photon beam characteristics needed to be understood in radiation therapy at the time of commissioning of Treatment Planning system (TPS) as well as applying various treatment planning algorithms in clinical applications. In this study we measured the dose profiles of open field, physical wedges (PW) and virtual wedges (VW) for energies (6 MV & 15 MV), various field sizes (10 × 10, 15 × 15 & 20 × 20 cm2), depths (dmax, 10 cm, 20 cm) and wedge angles (15°, 30°, 45° and 60°). From beam profile we calculated the penumbral width for open and wedged fields. The study was carried out on Siemens ONCOR IMRT Plus linear accelerator. The obtained penumbral width of PW and VW of all wedge angles was subtracted from the penumbral width of open field. The deviations in penumbral width were compared and statistically analyzed as a function of energy, depth, field size and wedge angles. Material and Method: The penumbral width was measured using IBA CC13 ion chamber in IBA Blue phantom (a 3D water phantom). The source to surface distance (SSD) during our study was kept 100cm and measurement was taken for 10 × 10, 15 × 15, 20 × 20 cm2 field sizes and for 15°, 30°, 45°, 60° wedges. These measurements were taken for both 6 MV and 15 MV photon energies. Virtual wedge profiles were acquired using LDA-99 linear detector array (IBA, Germany). The deviations in penumbral width for both PW and VW were calculated by subtracting the penumbral width from open field penumbral width in gun direction (in-plane) and deviation in VW penumbral width, and were obtained by subtracting the open field penumbral width in left-right direction (cross-plane) direction. The measured deviations were plotted for both PW and VW. Statistics on the measured deviations was performed by using SPSS Version 15. Results & Conclusion: The results of one way ANOVA (Analysis of Variance) show that the deviations are significant with energy and the deviations are higher in lower energy than higher energy. The deviations increase as depth increases, the deviations are also significant with depth. The deviations increase with field sizes; the deviations as a function of field size are highly significant. The deviations are higher in PW than VW but the deviations with wedge type are in-significant. As wedge angle increases, deviations also increase and the effect of wedge angle is highly significant on deviations.

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Farrukh, S. , Ilyas, N. , Naveed, M. , Haseeb, A. , Bilal, M. , Najamuddin, D. and Iqbal, J. (2017) Penumbral Dose Characteristics of Physical and Virtual Wedge Profiles. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 6, 216-224. doi: 10.4236/ijmpcero.2017.62020.

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