ESTRO 2024 - Abstract Book

S2050

Clinical - Paediatric

ESTRO 2024

for children as young as five years old [5]. Hence, DIBH as a dose-sparing strategy to normal tissue is relevant for pediatric patients as many become long-term survivors [6–9]. The TEDDI trial (Radiotherapy Delivery in Deep Inspiration for Paediatric Patients: a NOPHO Feasibility Study) systematically introduce radiotherapy delivery in DIBH to pediatric patients. In this context, assessment of setup position uncertainties in DIBH and free-breathing (FB), respectively, is required. Here, we report the setup repeatability for pediatric patients treated with radiotherapy (RT) in either DIBH or FB using daily cone-beam CT (CBCT) - results of the TEDDI trial.

Material/Methods:

Seven consecutive patients in TEDDI were selected for this analysis. For all patients in TEDDI, a treatment plan in both DIBH and FB was calculated (both plans with optimal target coverage), and the plan with the most sparing of organs at risk (e.g., heart, lungs, and female breasts) was chosen for treatment delivery. During treatment, all patients had daily CBCT imaging for setup verification. Setup repeatability was assessed through offline registration of the CBCT images to the planning CT images initially using automatic registration on sternum and anterior ribs followed by manual corrections based on soft tissue and target coverage. A delta value for offline and online registration was calculated for longitudinal, vertical, lateral and rotations (reported in cm). The length of delta correction vector was calculated and Levene’s test was performed in order to test for homogeneity of variance.

Results:

Four patients were treated in DIBH, and three patients were treated in FB. The two groups (DIBH and FB) were comparable in age (range: 14-16 years) and height (162-185 cm). The clinical tumour volume varied from 29 ml to 570 ml for both groups. Total number of fractions evaluated for DIBH and FB were 84 fractions and 43 fractions, respectively. Figure 1 is a scatterplot of the absolute delta for corrections in the seven patients and demonstrates no differences in the size and distribution of corrections. This was confirmed by Levene’s test which showed no significant difference for the two groups (p-value = 0,45).

Conclusion: