Comparison of calculation accuracy of the cadplan and alfard radiotherapy computer planning systems in Co – 60 teletherapy

Abstract Purpose The purpose of this work was to determine the agreement of the measured and calculated values of the isodose distance (depth) along the central axis and penumbra. Materials and methods Isodose distributions were measured with an ionization chamber in a water phantom. Photon beams were generated by a Co 60 teletherapy unit. Beam data were transferred to the treatment planning systems. The analysis was performed for open or 30, 45, 60 degree wedged fields, field sizes of 6 × 6 cm, 10 × 10 cm, 14 × 14 cm and SSD = 80 cm. The relative errors between the measured values and the calculated values by CADPLAN 2.7 and calculated by ALFARD were evaluated. Results In the case of open fields, the relative error of the calculated isodose depth along the central axis is comparable for both systems, whereas for wedged fields the relative error is smaller in CADPLAN calculations. Generally, both systems underestimate the calculated values as compared with those measured. The penumbra values are smaller for the CADPLAN system than those for the ALFARD. Conclusion Quantification of calculation accuracy constitutes an essential part of the verification of radiotherapy planning systems.