[Dosimetric impact of image-guided translational isocenter correction for 3-D conformal radiotherapy of the prostate].
OBJECTIVE
Interfractional prostate motion during radiotherapy due to variation in rectal distension can have negative consequences. The authors investigated the dosimetric consequences of a linear translational position correction based on image guidance when a three-dimensional conformal treatment technique was used.


METHODS
Planning CTs of seven patients with empty and distended rectum were analyzed. A reference plan for the planning target volume (PTV) and the boost were calculated on the CT dataset with the empty rectum with a standard four-field technique. The treatment plan was transferred to the CT with the distended rectum for an uncorrected setup (referenced to bony anatomy) and a corrected setup after position correction of the isocenter. The dosimetric consequences were analyzed.


RESULTS
Organ motion decreased the coverage of the prostate by the 95% isodose during simulated single treatment fractions by up to -21.0 percentage points (%-p; boost plan) and by up to -14.9%-p for the seminal vesicles (PTV plan). The mean rectum dose increased by up to 18.3%-p (PTV plan). Linear translational correction (mean 6.4 +/- 3.4 mm, maximum 10.8 mm) increased the coverage of the prostate by the 95% isodose by up to 12.7%-p (boost plan), while the mean rectum dose was reduced by up to -8.9%-p (PTV plan). For the complete treatment a reduction of complication probability of the rectum of approximately 5%-p was calculated.


CONCLUSIONS
The use of an image guidance system with linear translational correction can improve radiation treatment accuracy for prostate cancer, if geometric changes are within certain limits.
Wertz
Hansjoerg
H
Klinik für Strahlentherapie und Radioonkologie, Universitätsklinikum Mannheim, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Deutschland. hansjoerg.wertz@radonk.ma.uni-heidelberg.de
Lohr
Frank
F
Dobler
Barbara
B
Mai
Sabine
S
Wenz
Frederik
F
D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed