Radiobiological and dosimetric indices related effects of patient setup errors were evaluated for prostate patients treated using volumetric modulated arc therapy technique.
Materials and Methods:
Ten patients were treated and evaluated during the course of treatment. Each one was treated with 2 Gy for 39 fractions. The setup verification of each patient was determined using an electronic portal imaging device for 5 fractions during the treatment course. The mean of setup errors for those 5 fractions was calculated for each patient. Dose-Volume Histograms of the planning target volume, femoral heads, bladder and rectum were generated, and the conformity index, homogeneity index, tumor control probability, and normal tissue complication probability were determined.
The population random set-up errors were (3.61), (3.24), and (3.87) mm in vertical, longitudinal, and lateral directions respectively. Radiobiological indexes were evaluated witht and without inrtoduction of the random errors. In the original plan the average EUD in the VMAT plans was 77.59 Gy, and the average of TCP was 98.24%; but with the introduction of the errors, the average EUD became in the order of 60.24 Gy, while the average of TCP was in the order of 84.24%. Significant differences were observed between the two plans.

The dosimetric and biological impacts were evaluated and indicated that setup errors during VMAT treatments can lead to a non-significant change of conformity and homogeneity but can lead to changes in the dose distribution influencing the target volume coverage and altering the deliver dose to the organs at risk.