Ahmed Mohamed Hussein Mohamed*, Ismail Emam and Amer Mohamed
Treatment planning is one of the main steps in radiotherapy. It includes dose, isodose and monitor units (MUs) calculations. The dose calculation is based on algorithms implemented in the treatment planning system (TPS). For a suitable clinical use, these algorithms must calculate the dose as accurately as possible. The aim of this work is the assessment of treatment planning system installed in Aswan Oncology Institute to perform dosimetric validation of various parameters.
Measurements have been performed using existing Elekta linear accelerator, (scanditronix-wellhofer dosimetry) system, and water phantom. A variety of 3D conformal fields were created in Xio TPS on a combined Polymethyl methacrylate (PMMA) phantom and validated against measurements with a calibrated ion chamber. Some of the parameters such as (Tissue phantom ratio (TPR), surface dose, buildup, flatness, symmetry, penumbra, contamination dose) varied including source to surface distance, field size, gantry angle, and depth for all photon and electron energies. The difference between measurements and calculation of flatness and symmetry values at different electron energies were between -0.4% to 1.7% and 6 MV didn’t exceed ± 0.8%. The mean difference in value of penumbra of electron beams was -4.97% and 6 MV was ± 5%. TPR and surface dose at 6 MV increased with the field size (FS) increasing. All the resulted difference of measurements and calculation were in agreement with IAEA-TRS430 and Venselaar et al. which didn’t exceed ± 2% at flatness, symmetry and ±15% at penumbra. This investigation on dosimetric validation ensures accuracy of Xio TPS thereby improving patient safety.
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