Tangential breast irradiation: comparison of patient positioning and beam parameters after planning investigation at a CT scanner and a simulator with CT option.
OBJECTIVE
A prerequisite for the exact planning of a radiotherapy is the precise accordance of the patient positioning during the planning CT and the therapy simulation. How far possible differences between patient set-up during the planning CT at a therapy simulator with CT option or a conventional CT influence the planned dose distribution is investigated by the example of the tangential breast irradiation.


METHODS
In 18 patients transverse sections for treatment planning of tangential breast irradiation were made both using a diagnostic CT scanner and a therapy simulator with CT option. For patient positioning the patient outlines were compared. Furthermore, the treatment plans which were based independently on both transverse sections were compared.


RESULTS
In the mean deviations of 1 resp. 0 mm (SD = 7 resp. 8 mm) between the ventral and lateral outlines of the breast were found. The mean breast diameter between the Z-points was 5 mm wider in the simulator CT based plans (SD = 14 mm). The field width was 6 mm wider (SD = 8 mm), the beam angle 1 degree steeper (SD = 4 degrees). The calculated monitor units differed 1% (SD = 6%). None of the differences between measured parameters reached statistical significance. A significant correlation was only seen for the interrelated contours (anteroposterior and lateral diameters).


CONCLUSIONS
The results of this investigation show no difference between treatment set-up and treatment planning using information of a CT scanner or a simulator with CT option for tangential breast irradiation.
Schraube
P
P
Radiologische Klinik (Schwerpunkt Strahlentherapie), Universität Heidelberg.
Flentje
M
M
Wannenmacher
M
M
D001943:Breast Neoplasms / Q000532:radiotherapy*; D003198:Computer Simulation; D005260:Female; D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed