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 (d max ) 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 photon 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 between 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.
Highlights
Radiation therapy is the method for the treatment of cancer in which about 60% of patients require radiotherapy as curative or palliative intent.[1]
In computerized treatment planning system TPS, the most important software component is the dose calculation algorithm which is responsible for the precise delivery of dose to target volume, and it may be linked to the calculation of monitor units (MUs)
The highest difference of our results is lower than Venselaar et al 7 and lower than Caprile et al 23, and reaches up to 28.5% for pencil-beam convolution (PBC) for field size 20 × 20
Summary
Radiation therapy is the method for the treatment of cancer in which about 60% of patients require radiotherapy as curative or palliative intent.[1] The radiation dose must be delivered 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 responsible 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 (3DCRT) 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 radiations to the tumor and reduce the exposure of normal tissues.[4, 5]. The reason for using these asymmetric fields is that the patient set-up becomes more accurate because the isocenter does not have to be shifted, for instance if abutting fields are applied.[8]
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