Page 102 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

Therefore, in this study we aimed to quantify the inter- and intrafractional variability of respiratory-induced diaphragm motion in adults, using the exact same methodology as used in our pediatric study [16]. The pooled analysis of pediatric and adult data enables a methodologically consistent comparison of respiratory motion characteristics in children and adults in order to reveal if 4DCT application for planning purposes in children could be valid.
6.2 | Methods
Patient data
Pediatric data was available from our previous study, where respiratory-induced diaphragm motion was retrospectively analyzed during the treatment course of 45 children (median age 11; range 2-18 years) [16]. We collected information on general anesthesia (GA, n=7), and patient characteristics including age at the first radiation treatment fraction, height, weight, primary cancer diagnosis and radiation site. A detailed overview of pediatric patient characteristics is given in Huijskens et al. [16] and added in Supplementary Table 6.1. For this pooled analysis, 45 adults (median age 63; range 34- 93 years), treated at our institute within the same period (2010-2016) as the pediatric group, were randomly included when the diaphragm was visible in upper abdominal or thoracic free-breathing cone beam computed tomography (CBCT) scans. To prevent bias when comparing the respiration pattern in the adult group to that of the pediatric group, lung cancer patients were excluded. Thus, the selection yielded esophageal (n=13), gastric (n=17), and pancreatic (n=15) cancer patients. Supplementary Table 6.2 provides a detailed overview of the adult patient characteristics. In our institute, abdominal compression to control respiratory motion is neither used in children, nor in adults. A general overview of all patient characteristics can be found in Table 6.1.
CBCT acquisition
In our pediatric study, a total of 480 pediatric CBCTs (median 7; range 4–32 per patient) were included [16]. Acquisition parameters for pediatric CBCTs were 120 kV, 10 mA, and 10 or 40 ms exposure time per projection. The rotation varied from 200 (n=35) to 360 (n=10) degrees, resulting in a variation in number of projection images per CBCT (180–760). Adult patients received daily or weekly CBCT imaging (Synergy, Elekta Oncology systems, Crawly, UK) prior to treatment for position verification, totaling 524 CBCTs (median 11; range 2-30 per patient). Acquisition parameters for adult CBCTs were 120 kV, 10 mA, and 10 or 40 ms exposure time per projection. For all adults, the rotation yielded 360 degrees, resulting in approximately 760 projection images per CBCT.
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