Purpose/Objective(s):In external radiotherapy even with appropriate immobilization devices, there are substantial interfractional changes of body configuration. Although image-guided radiotherapy (IGRT) is widely used to determine and to correct the daily setup error, the additional interpretation for image registration should provide additional variability. We correlated daily setup errors with variability of image registration and body configuration in IGRT.Materials/Methods:The subjects consisted of 12 consecutive patients treated with IGRT for their esophageal cancer. Two radiation therapists had consensually achieved daily 3D registration between planning computed tomography (CT) and cone beam CT (CBCT). The original data sets of image registration in all fractions but boost irradiations with isocenter alternation were selected for evaluation. There were 20 to 32 data sets in each patient: a total of 318 data sets. To evaluate daily setup errors, the mean 3D displacement vector and random errors (standard deviation: SD) along the three directions were calculated in each patient. An experienced radiation therapist reviewed the data sets to assess the reproducibility of image registration, and recorded geometric differences as interobserver variability. To characterize the body configuration on daily CBCT, we measured depth on the isocenter plane, interscapular space, shoulder position along the superior-inferior (SI) direction, vertebral tilt along the anterior-posterior (AP) direction, and pillow position along the SI direction. Pearson correlation analysis was used to evaluate the relationship between parameters.Results:The mean 3D displacement vectors ranged from 4.9 to 15.5 mm for daily setup and 0.7 to 2.1 mm for interobserver variability in image registration. There was a positive correlation between the 3D vectors for setup and image registration (r = 0.583, p = 0.047). Concerning daily changes of body configuration (SD), depth and shoulder position were positively correlated with setup error (SD) along SI direction (Table). Furthermore, there was significant positive correlation between daily shoulder position and setup displacement along SI direction in 8 of the 12 patients.Conclusions:The setup error should disturb the image registration in IGRT. Shoulder position is an important factor for the reproducibility of setup in thoracic radiotherapy.Coefficients for correlations between variability of body configuration and setup in 12 patientsBody configurationSetup error (SD)LRSIAPDepth (SD)-0.1830.799*-0.098Interscapular space(SD)-0.2930.1460.001Shoulder position (SD)0.2050.715**-0.304Vertebral tilt (SD)-0.1980.4350.049Pillow position (SD)-0.1250.351-0.174SD = standard deviation*p = 0.002, **p = 0.009 (Pearson correlation analysis)
Kai, N,
Correlation of Daily Setup with Image Registration and Body Configuration in Image-guided Radiotherapy. Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL.
http://archive.rsna.org/2014/14045811.html
