Active breathing control (ABC): determination and reduction of breathing-induced organ motion in the chest.
OBJECTIVE
Extensive radiotherapy volumes for tumors of the chest are partly caused by interfractional organ motion. We evaluated the feasibility of respiratory observation tools using the active breathing control (ABC) system and the effect on breathing cycle regularity and reproducibility.


METHODS
Thirty-six patients with unresectable tumors of the chest were selected for evaluation of the ABC system. Computed tomography scans were performed at various respiratory phases starting at the same couch position without patient movement. Threshold levels were set at minimum and maximum volume during normal breathing cycles and at a volume defined as shallow breathing, reflecting the subjective maximal tolerable reduction of breath volume. To evaluate the extent of organ movement, 13 landmarks were considering using commercial software for image coregistration. In 4 patients, second examinations were performed during therapy.


RESULTS
Investigating the differences in a normal breathing cycle versus shallow breathing, a statistically significant reduction of respiratory motion in the upper, middle, and lower regions of the chest could be detected, representing potential movement reduction achieved through reduced breath volume. Evaluating interfraction reproducibility, the mean displacement ranged between 0.24 mm (chest wall/tracheal bifurcation) to 3.5 mm (diaphragm) for expiration and shallow breathing and 0.24 mm (chest wall) to 5.25 mm (diaphragm) for normal inspiration.


CONCLUSIONS
By modifying regularity of the respiratory cycle through reduction of breath volume, a significant and reproducible reduction of chest and diaphragm motion is possible, enabling reduction of treatment planning margins.
Gagel
Bernd
B
Department of Radiotherapy, RWTH Aachen University, Aachen, Germany. BGagel@UKAachen.de
Demirel
Cengiz
C
Kientopf
Aline
A
Pinkawa
Michael
M
Piroth
Marc
M
Stanzel
Sven
S
Breuer
Christian
C
Asadpour
Branka
B
Jansen
Thomas
T
Holy
Richard
R
Wildberger
Joachim E
JE
Eble
Michael J
MJ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003964:Diaphragm / Q000000981:diagnostic imaging*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008482:Mediastinum / Q000000981:diagnostic imaging; D008875:Middle Aged; D009068:Movement; D015203:Reproducibility of Results; D012119:Respiration; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D035441:Thoracic Wall / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D014132:Trachea / Q000000981:diagnostic imaging