TITLE:
Penumbral Dose Characteristics of Physical and Virtual Wedge Profiles
AUTHORS:
Salman Farrukh, Nasir Ilyas, Muhammad Naveed, Abdul Haseeb, Muhammad Bilal, Dr Najamuddin, Javed Iqbal
KEYWORDS:
Physical Wedge, Virtual Wedge, Penumbra and Deviations
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.6 No.2,
May
27,
2017
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.