Variations in 60Co γ-ray Radiotherapy Surface Dose with Physical Wedge

Document Type : Original Article


1 Department of Physics, Sana’a University, Sana’a, Yemen

2 Physics Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo 11884, Egypt.


THE purpose of this study was focused on examining the influence of various physical wedge filters on the surface dose with various field sizes for 60Co γ-ray beam, which have been used to treat a variety of cancer worldwide, especially in developing countries. The percentage depth dose in build-up region for open and physical wedged beams were measured by a Markus chamber, which was irradiated by a 60Co beam. Irradiations were performed in a virtual water phantom at various depths for field sizes range from 4.5×4.5 up to 15×15 cm2. The polarity effect and the over-response correction factor were applied for Markus chamber. For open and wedge beams angles 15°,30° ,45° , and 60°, the percentage surface dose found to be 25.95%±0.17%, 24.59 % ± 0.06 %,24.08%±0.01% ,23.71%±0.05% , and 24.45%±0.11%, respectively, at 10×10 cm2 field size. So, their variations at same field were 1.36%,,2.24% 1.87% and 1.5% , respectively. The percentage surface dose decreased as the wedge angle increased for all field sizes. The percentage uncertainty for all data is 0.16%. The increase in the percentage dose at surface and build-up region with various field sizes for both open and wedged beams was due to electron contamination from the head of the treatment machine and air. However, a significant effect is seen for physical wedged beams, due to physical wedge eliminates secondary electrons at the same time generates new electrons.


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