CT simulation in nodal positive breast cancer.
BACKGROUND
A variety of solutions are used to match tangential fields and opposed lymph node fields in irradiation of nodal positive breast cancer. The choice is depending on the technical equipment which is available and the clinical situation. The CT simulation of a non-monoisocentric technique was evaluated in terms of accuracy and reproducibility.


METHODS
The field match parameters were adjusted virtually at CT simulation and were compared with parameters derived mathematically. The coordinate transfer from the CT simulator to the conventional simulator was analyzed in 25 consecutive patients.


RESULTS
The angles adjusted virtually for a geometrically exact coplanar field match corresponded with the angles calculated for each set-up. The mean isocenter displacement was 5.7 mm and the total uncertainty of the coordinate transfer was 6.7 mm (1 SD). Limitations in the patient set-up became obvious because of the steep arm abduction necessary to fit the 70 cm CT gantry aperture. Required modifications of the arm position and coordinate transfer errors led to a significant shift of the marked matchline of > 1.0 cm in eight of 25 patients (32%).


CONCLUSIONS
The virtual CT simulation allows a precise and graphic definition of the field match parameters. However, modifications of the virtual set-up basically due to technical limitations were required in a total of 32% of cases, so that a hybrid technique was adapted at present that combines virtual adjustment of the ideal field alignment parameters with conventional simulation.
Horst
E
E
Department of Radiation Oncology, University of Münster, Germany. horste@uni-muenster.de
Schuck
A
A
Moustakis
C
C
Schaefer
U
U
Micke
O
O
Kronholz
H L
HL
Willich
N
N
D001943:Breast Neoplasms / Q000532:radiotherapy*; D003196:Computer Graphics; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008962:Models, Theoretical; D010315:Particle Accelerators; D011880:Radiotherapy Planning, Computer-Assisted; D016683:Supine Position; D013997:Time Factors; D014057:Tomography, X-Ray Computed