Journal of Medical Physics
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ORIGINAL ARTICLE
Year : 2010  |  Volume : 35  |  Issue : 1  |  Page : 33-41

Studying wedge factors and beam profiles for physical and enhanced dynamic wedges


1 Institute of Nuclear Medicine Oncology and Radiotherapy (INOR), Abbottabad; Institute of Radiotherapy and Nuclear Medicine (IRNUM), Peshawar, Pakistan
2 TBCC, Department of Medical Physics, 1331-29 street, NW Calgary, AB, Canada
3 Department of Physics, Kyungpook National University, Daegu 702-701, Republic of Korea, Korea
4 Institute of Nuclear Medicine Oncology and Radiotherapy (INOR), Abbottabad, Pakistan
5 Head NTSG, Pakistan Institute of Nuclear Science and Technology (PINSTECH), Nilore, Islamabad, Pakistan

Correspondence Address:
Misbah Ahmad
Institute of Radiotherapy and Nuclear Medicine (IRNUM), Peshawar
Pakistan
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-6203.57116

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This study was designed to investigate variation in Varian's Physical and Enhanced Dynamic Wedge Factors (WF) as a function of depth and field size. The profiles for physical wedges (PWs) and enhanced dynamic wedges (EDWs) were also measured using LDA-99 array and compared for confirmation of EDW angles at different depths and field sizes. WF measurements were performed in water phantom using cylindrical 0.66 cc ionization chamber. WF was measured by taking the ratio of wedge and open field ionization data. A normalized wedge factor (NWF) was introduced to circumvent large differences between wedge factors for different wedge angles. A strong linear dependence of PW Factor (PWF) with depth was observed. Maximum variation of 8.9% and 4.1% was observed for 60° PW with depth at 6 and 15 MV beams respectively. The variation in EDW Factor (EDWF) with depth was almost negligible and less than two per cent. The highest variation in PWF as a function of field size was 4.1% and 3.4% for thicker wedge (60°) at 6 and 15 MV beams respectively and decreases with decreasing wedge angle. EDWF shows strong field size dependence and significant variation was observed for all wedges at both photon energies. Differences in profiles between PW and EDW were observed on toe and heel sides. These differences were dominant for larger fields, shallow depths, thicker wedges and low energy beam. The study indicated that ignoring depth and field size dependence of WF may result in under/over dose to the patient especially doing manual point dose calculation.


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