ESTRO 2024 - Abstract Book

S4008

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

whole liver silhouette was delineated on every CBCT, planning CT and diagnostic imaging (CT, n = 9; MRI, n = 2). Dice Similarity Coefficient was estimated between diagnostic imaging or CBCT matched with the planning CT scan.

Figure 1: Patient with atypical carcinoid of the liver positioned for 4D planning CT scan while receiving CPAP ventilation. Tolerability was satisfactory, even in comparatively frail patients.

Results:

CPAP ventilation was well tolerated by all patients. Lung volume was increased during CPAP ventilation by a mean of 1057,2 ml (p < 0.05) compared to diagnostic imaging (Figure 2). CPAP ventilation was non-inferior to other methods of diaphragmal motion management regarding amplitude of the right diaphragm (mean 1.61 cm vs 1.43 cm), left diaphragm (mean 1.46 cm vs 1.5 cm) and tumor (mean 0.69 cm vs 0.91 cm). Although observed by radiological technologists, we found no statistical evidence for inferior motion management when stratifying for BMI. This might be due to low sample size.

Mean DICE of the liver in interfraction CBCT was 0.85 and mean DICE after matching with diagnostic imaging was 0.86.

In one patient with adrenal gland SBRT we observed a larger distance between adrenal gland and small bowel during CPAP ventilation compared with abdominal compression. Due to this increase in distance, no compromise between dose prescription to the PTV and dose de-escalation due to safety concerns was necessary.