Accuracy Evaluation of Isogray TPS Dose Calculations in Symmetric and Asymmetric Fields of the Elekta Compact Linear Accelerator

Radiation therapy is one of the most important methods of cancer treatment. Radiation therapy uses symmetric and asymmetric fields in which the radiation dose distribution is different. To calculate the dose distribution, computer treatment planning systems are used which must have acceptable calculations accuracy. The aim of this study was to investigate the accuracy of the dose calculated by the Isogray treatment planning system in symmetric and asymmetric fields in the water phantom using ionization chamber dosimeter.

Practical measurements were performed by a Semiflex ionization chamber dosimeter in the PTW-MP3 water phantom. Depth dose data on the central axis of the beam and dose profile at a depth of 10 cm, for square fields with dimensions of 5 × 5, 10 × 10, 15 × 15, 20 × 20 and 30 × 30 cm and rectangular fields 20 × 8 And 15 × 10 cm and half beam fields with dimensions of 6 × 10 and 7 × 15 cm were measured. Corresponding data were extracted from the treatment planning system and compared with each other by gamma index.

Dosimetric data and treatment planning system were in good agreement for depth dose percentage and dose profile, and for almost all points, the gamma index value was less than one with strict criteria of 2% dose difference and 2 mm difference in distance.

The results show the acceptable accuracy of Isogray treatment planning system in dose calculations for symmetric and asymmetric open fields in homogeneous water phantoms.