Interfractional and intrafractional accuracy during radiotherapy of gynecologic carcinomas: a comprehensive evaluation using the ExacTrac system.
OBJECTIVE
To evaluate positioning uncertainties with an infrared body marker-based positioning system (ExacTrac) compared with conventional laser positioning in patients treated for gynecologic carcinomas, and to investigate patient movement during therapy.


METHODS
Ten patients were positioned both with a conventional laser system and with the ExacTrac system. Positioning accuracy was evaluated using repeated electronic portal images. Average displacements and overall, systematic, and random errors were calculated and compared for the two positioning methods. Further, inter- and intrafractional patient movement including time trends in positioning displacements, respiratory amplitudes, and breathing frequencies were analyzed by online documentation of body marker movement with the ExacTrac system.


RESULTS
Average displacements ranged between -3.6 and 6.7 mm for the three coordinates. Mean systematic and random errors ranged from 1.6 to 3.7 mm and 2.2 to 3.7 mm, respectively, with no significant differences between conventional and ExacTrac positioning (p > 0.07). The main breathing direction was from dorsocaudal to anterocranial in 9 of 10 patients. The mean 3D breathing amplitude in the pelvis was 2.4 mm (0.49-6.96 mm). Significant interfractional and intrafractional time trends were observed concerning breathing amplitudes and positioning displacements.


CONCLUSIONS
The observed displacements did not vary significantly between the two evaluated positioning systems. The analysis of registered body marker positions revealed a wide variation in respiratory frequencies, breathing amplitudes, and patient displacements with interfractional and intrafractional time trends. Systems that allow the measurement of each patient's motion characteristics are a necessary requirement for all efforts at individually tailored radiation therapy.
Weiss
Elisabeth
E
Department of Radiotherapy, University of Goettingen, Goettingen, Germany. eweiss@gwdg.de
Vorwerk
Hilke
H
Richter
Susanne
S
Hess
Clemens F
CF
D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma / Q000532:radiotherapy*; D003198:Computer Simulation; D004389:Durable Medical Equipment; D004867:Equipment Design; D005260:Female; D005833:Genital Neoplasms, Female / Q000532:radiotherapy*; D006801:Humans; D007834:Lasers; D008875:Middle Aged; D009068:Movement; D011187:Posture; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D015203:Reproducibility of Results; D014743:Videotape Recording