ESTRO 2023 - Abstract Book

S1693

Digital Posters

ESTRO 2023

Conclusion The results indicate potential benefit of asymmetrical margins for the cranial and caudal parts of the target, and that there is little difference between margins needed for FB and DIBH treatments, except for lymph node targets.

PO-1938 Organ motion in thorax and abdomen during radiotherapy: a multicenter study in 188 children

K. Meijer 1,2 , I. van Dijk 1,2 , M. Frank 1 , A. van den Hoek 1 , B. Balgobind 1,2 , G. Janssens 3,4 , M. Wendling 5 , J. Maduro 6,3 , A. Bryce Atkinson 7 , A. Loginova 8 , A. Bel 1,2 1 Amsterdam UMC, University of Amsterdam, Radiation Oncology, Amsterdam, The Netherlands; 2 Cancer Center Amsterdam, Cancer Treatment and Quality of Life, Amsterdam, The Netherlands; 3 Princess Máxima Center, Pediatric Oncology, Utrecht, The Netherlands; 4 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands; 5 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands; 6 University Medical Center Groningen, University of Groningen, Radiation Oncology, Groningen, The Netherlands; 7 School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom; 8 Federal Research and Clinical Center of Pediatric Hematology, Oncology and Immunology, Radiation Oncology, Moscow, Russian Federation Purpose or Objective For accurate radiotherapy of thoracic and abdominal tumors, organ motion needs to be considered. Present research on organ motion in pediatric patients is limited to rather small cohorts. Therefore, we aimed to quantify interfractional diaphragm and abdominal organ motion, and intrafractional motion of the right hemidiaphragm in a large international cohort of pediatric cancer patients (<18 years). We also investigated possible correlations of motion with age and general anesthesia (GA). Materials and Methods In 188 children (median age 7.0; range 0.4–17.9 years) from six institutes, interfractional motion of both hemidiaphragms, spleen, liver and both kidneys was quantified using a two-step registration; CBCTs were registered to the reference CT (refCT) relative to the bony anatomy, followed by registration of the organ. We calculated the group mean, and the distributions of systematic and random errors (standard deviations Σ and σ , respectively) in CC, LR and AP directions. To quantify intrafractional motion (CC direction) in a subcohort of 79 children (median age 7.6; range 1.0–17.8 years), we used a semi-automated method selecting inhale and exhale positions of the right hemidiaphragm peak, and calculated the difference between the peaks (breathing amplitude). We investigated the correlation of inter- and intrafractional motion with age (Spearman’s ρ ), and the difference in motion between patients ≥ 5.5 years, and patients <5.5 years treated with and without GA. Results The group mean interfractional motion was largest in CC direction, but for all structures <1 mm, and not significantly different from the refCT (Bonferroni’s adjusted p>0.008). For all structures, we found no correlation between interfractional motion and age ( ρ <0.1; p>0.05). Mean interfractional motion of the right hemidiaphragm in patients treated with GA was significantly smaller than in those treated without GA (all <5.5 years; p=0.004), resulting in smaller Σ and σ values (Table 1). For intrafractional motion, the breathing amplitudes in children ≥ 5.5 years were significantly larger compared to patients <5.5 years treated without GA (p=0.02) (Table 2). In patients <5.5 years treated with GA, the breathing amplitudes (and random errors) were smaller compared to those treated without GA (Table 2), but there was no significant difference (p=0.4). We found a moderate but significant correlation between breathing amplitude and age ( ρ =0.43; p<0.001).