ACCURACY OF FIELD ALIGNMENT IN ABDOMINAL RADIATION-THERAPY

Purpose: To assess the accuracy of field alignment in a homogeneous gr oup of patients undergoing radiotherapy of the abdomen (adjuvant treat ment of the paraaortic region in Stage I testicular seminoma), To eval uate the predictive value of the first verification on field placement errors during subsequent treatment delivery, Methods acid Materials: In 45 patients, linear and rotational discrepancies were measured betw een simulation and first check and between 10 consecutive verification films, Results: For the total group of patients, the distribution of all deviations showed mean values between 2.3 mm and -2.7 mm with stan dard deviations of 3.9 mm to 4.7 mm for linear discrepancies, and -0.5 degrees to 0.3 degrees with standard deviations of 1.2 degrees to 2.1 degrees for rotational discrepancies, respectively. For ail patients, deviations for the transition from simulator to the treatment machine were similar to deviations during subsequent treatment delivery, with 95% of all absolute deviations < 10.0 mm and 4 degrees, respectively, When performing correlation analysis between deviations at first chec k and during treatment delivery, a correlation for lateral displacemen ts and a borderline correlation for caudal displacements could be foun d, There was no correlation for cranial and rotational displacements, Conclusions: Although a trend of deviations for subsequent treatment d elivery may be shown at first check, our analysis indicates that the f irst verification cannot reliably predict inaccuracies during treatmen t delivery, Random fluctuations of field displacements of up to 1.0 cm prevail, They must be considered when prescribing the safety margins of the planned target volume and determining cutoff points for correct ive actions in abdominal radiation therapy.