The dependency of wedge factors on field size and depth in megavoltage beams
Avadhani, J.S.; Pradhan, A.S.; Sankar, A.; Viswanathan, P.S.
Strahlentherapie und Onkologie Organ der Deutschen Rontgengesellschaft . 172(11): 626-630
1996
ISSN/ISBN: 0179-7158 PMID: 8946032 Document Number: 464143
Aim: To investigate the variation of wedge factors on field size, depth on 2 types of telecobalt units and 3 types of medical linear accelerators and to make a simplified approach for day to day calculation procedure. Materials and Methods: A 0.125 cm-3 ion chamber was used to determine the wedge factors which is connected to the computer controlled radiation field analyser. The wedge factors were determined for field sizes varying from 5 times 5 cm to the maximum square field size available for each wedge angles and at multiple depths upto 25 cm of respective teletherapy units. The results obtained are fitted to a second degree polynomial function. Results: There is no significant variation of wedge factor on field size for all the 3 linear accelerators. The wedge factors are found to vary mainly at larger depths and wedge angles. The variation of wedge factors for 2 types of cobalt units were similar and increase of 3%, 4% and 5.5% is observed for wedge angles 30 degree , 45 degree and 60 degree respectively with respect of depth of maximum build-up. The trend was similar for linear accelerators with maximum increase in wedge factor up to 7.5% for 60 degree wedge angle at 25 cm depth for 6 MV photon beams. Discussion and Conclusions: The determination of wedge factors at various field sizes and depths is essential to ensure accurate dose delivery. With experimental wedge data fitted with second degree polynomial function is a simplified and alternative method which can be adopted for routine dosimetric calculations.