International Journal of Cancer Therapy and Oncology www.ijcto.org Corresponding author: Tamer Dawod; Department of Clinical Oncology and Nuclear Medicine, Faculty of Medicine, Mansoura University, Mansoura, Egypt. Cite this article as: Dawod T. Treatment planning validation for symmetric and asymmetric motorized wedged fields. Int J Cancer Ther Oncol 2015; 3(1):030118. DOI: 10.14319/ijcto.0301.18 © Dawod ISSN 2330-4049 Treatment planning validation for symmetric and asymmetric motorized wedged fields Tamer Dawod Department of Clinical Oncology and Nuclear Medicine, Faculty of Medicine, Mansoura University, Mansoura, Egypt Received October 24, 2014; Revised December 25, 2014; Accepted January 05, 2015; Published Online January 20, 2015 Technical Report Abstract Purpose: Wedged beam are often used in clinical radiotherapy to compensate missing tissues and dose gradients. The Elekta Precise linear accelerator supports an internal motorized wedge, which is a single large, physical wedge on a motorized carriage. In this study, the dosimetric performance of Elekta precise three dimensional treatment planning system (3DTPS) is evaluated by comparing the calculated and measured doses. Methods: The calculations were performed by the 3DTPS for symmetric as well as asymmetric fields in a source to skin distance (SSD) setup at the depth of maximum dose (dmax) as well as at 5, 10, and 20 cm depths in water phantom using 60° motorized wedges for field sizes of 4 × 4, 10 × 10, and 20 × 20 cm 2 for 6 and 15 MV pho- ton beams. Measurements were produced by Elekta Precise linear accelerator using 0.125 cc volume ionization chamber. Results: Good agreement between the measured and calculated isodose lines were found, with the maximum difference not exceed 5%. The difference between the calculated and measured data increases as the field size decreases, and the deviation in symmetric setting was less than that of asymmetric setting. The increase in wedge angle led to increase in the difference be- tween calculated and measured data. Conclusion: The results from this study showed that the accuracy of Elekta Precise 3DTPS used with the motorized wedges for symmetric and asymmetric fields is adequate for the clinical applications under the studied experimental conditions. Keywords: Radiotherapy; Motorized Wedge; Linear Accelerator Introduction Radiation therapy is the method for the treatment of cancer in which about 60% of patients require radiotherapy as cura- tive or palliative intent. 1 The radiation dose must be deliv- ered within ±5% of the prescribed dose. 2, 3 In computerized treatment planning system TPS, the most important software component is the dose calculation algorithm which is re- sponsible for the precise delivery of dose to target volume, and it may be linked to the calculation of monitor units (MUs). Three-dimensional conformal radiotherapy (3D- CRT) uses certain beam shaping devices in order to confirm the shape of beam to the target area of the patient. The target of such technique is to deliver high doses of energetic radia- tions to the tumor and reduce the exposure of normal tis- sues. 4, 5 Commissioning of the dose calculation algorithms of a treatment planning system is generally performed: (i) by entering basic beam data into the system according to the methods and requirements described in the user's manual of the system; and (ii) by comparing the results of dose calcula- tions with the entered data and with data that were meas- ured specially for this purpose. 6 Differences between calcu- lated and actual dose values may be encountered, partly due to uncertainties in the measured data, and partly due to im- perfect beam modeling. 7 A number of complex irradiation techniques apply wedged asymmetric high-energy photon beams. The reason for using these asymmetric fields is that the patient set-up becomes more accurate because the iso- center does not have to be shifted, for instance if abutting fields are applied. 8 Wedges are commonly used as beam-modifying devices in radiation therapy to optimize the target volume dose distri- bution .9, 10 Physical wedges have been used for many decades. Further developments in the head design have brought the concept of “universal wedges (UW) and motorized wedge (MW)”. MW is a single physical wedge (60°) which could generate desired angle (0 to 60°) with the combination of open and wedged beam. 11 Venselaar et al. 7 recently showed for a number of commercial treatment planning systems, that the algorithms for calculating monitor units (MUs) in wedged asymmetric fields have their limitations. Deviations up to 13% between the calculated and measured dose values were observed and had different magnitudes at the thin and