Image guidance and interfractional anatomical variation in paediatric abdominal radiotherapy

Abstract

Objectives: To identify variables predicting interfractional anatomical variations measured with cone-beam CT (CBCT) throughout abdominal paediatric radiotherapy, and to assess the potential of surface-guided radiotherapy (SGRT) to monitor these changes.

Methods: Metrics of variation in gastrointestinal (GI) gas volume and separation of the body contour and abdominal wall were calculated from 21 planning CTs and 77 weekly CBCTs for 21 abdominal neuroblastoma patients (median 4 years, range: 2 - 19 years). Age, sex, feeding tubes, and general anaesthesia (GA) were explored as predictive variables for anatomical variation. Furthermore, GI gas variation was correlated with changes in body and abdominal wall separation, as well as simulated SGRT metrics of translational and rotational corrections between CT/CBCT.

Results: GI gas volumes varied 74 ± 54 ml across all scans, while body and abdominal wall separation varied 2.0 ± 0.7 mm and 4.1 ± 1.5 mm from planning, respectively. Patients < 3.5 years (p = 0.04) and treated under GA (p < 0.01) experienced greater GI gas variation; GA was the strongest predictor in multivariate analysis (p < 0.01). Absence of feeding tubes was linked to greater body contour variation (p = 0.03). GI gas variation correlated with body (R = 0.53) and abdominal wall (R = 0.63) changes. The strongest correlations with SGRT metrics were found for anterior-posterior translation (R = 0.65) and rotation of the left-right axis (R = -0.36).

Conclusions: Young age, GA, and absence of feeding tubes were linked to stronger interfractional anatomical variation and are likely indicative of patients benefiting from adaptive/robust planning pathways. Our data suggest a role for SGRT to inform the need for CBCT at each treatment fraction in this patient group.

Advances in knowledge: This is the first study to suggest the potential role of SGRT for the management of internal interfractional anatomical variation in paediatric abdominal radiotherapy.

Figure 1.

Definition of the metrics of interfractional anatomical change and surface correction between planning computed tomography (CT) and cone-beam CT (CBCT).

Figure 2.

Example of variability in gastrointestinal gas and body contour between planning computed tomography (CT) and multiple weekly cone beam CT (CBCT) scans (Gas_std = 171 ml for this subject).

Figure 3.

Boxplots of gastrointestinal (GI) gas volume (Gas_std) variation according to age and general anaesthesia (GA), and body contour variation (Body_avg) according to absence or presence of feeding tubes. Outliers represent values outside 1.5x the interquartile range.

Figure 4.

Correlation between gastrointestinal gas variation (Gas_rel) and metrics of body change (Body_avg), abdominal wall change (Surface_avg) and surface correction metrics (t_x,y,z and r_x,y,z). Gas_rel ⁺ indicates the correlations when the CT scan was excluded from the analysis.

Figure 5.

a ) Distribution of values measured for surface correction metrics (t_x,y,z and r_x,y,z) and b) linear regression with gastrointestinal gas variation (Gas_rel).