Calculation of wedged dose distributions using an analytical method

Document Type: Conference Proceedings

Authors

1 Nuclear engineering unit, Department of Energy Engineering, Sharif University of Technology, Tehran, Iran.

2 Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran.

3 Physics Unit, Department of Radiotherapy and Oncology, and Ionizing and Non-Ionizing Radiation Protection Research Center, Shiraz University of Medical Sciences, Shiraz, Iran

4 Medical Physics Unit, Department of Medical Physics and Environment Health, Shahid Sadoghi University of Medical Sciences, Yazd, Iran

Abstract

Introduction:
Wedge filters are used in radiotherapy to modify photon beam and improve dose uniformity in the target volume. Determination of wedge dose distribution is important to improve treatment planning accuracy. The utilization of treatment planning software to obtain dose distribution is not always available. In this work an analytical model has been developed to calculate wedge dose distribution and the resulting isodose curves.
Materials and Methods:
The analytical method can be calculated the dose at any point (off axis and in axis) and for each wedge angle and field size with a given dose at any point of phantom. The calculated doses were converted to isodose curves with MATLAB software and validated with Elekta motorized wedge (MW) and Cobalt physical wedge (PW). Isodose wedge curves were measured using a 2-D profiler detector for Cobalt unit and a diode detector for Elekta linac.
Results:
The mean difference between analytical isodose curves and measurements for Elekta motorized wedge was 1.8% and for Cobalt physical wedge was within 3%. The differences were in agreement with ICRU criteria.
Conclusion:
The analytical method can be used as a fast and handy method for calculating dose at any off axis points and depth dose.

Keywords