ESTRO 2023 - Abstract Book

S85

Saturday 13 May

ESTRO 2023

There has been a reluctance to use daily cone beam CT (CBCT) in paediatric radiotherapy (RT), due to the fear of secondary cancers. Surveys report wide variation in practice for paediatric image-guided RT (IGRT), but they have never collected important technical information, such as exposure settings for specific anatomical sites. Here we report, for the first time, technical acquisition parameters from paediatric CBCT protocols throughout Europe for brain/head and abdominal sites. Materials and Methods We conducted a survey via the SIOPe network of paediatric radiation oncologists. The survey was reviewed by the SIOPe Radiation Oncology Working Group before distribution. We collected data via Qualtrics from 6th Sep to 22nd Oct 2022. The survey consisted of three parts: 1) each centre’s demographic information, 2) CBCT settings for brain/head sites, and 3) CBCT settings for abdominal sites. Quantitative data on technical exposure settings were assessed with descriptive statistics. Limitations of CBCT usages and dose reduction strategies were expressed in free text and assessed qualitatively. Results We received 51 responses from 25 European countries. 44/51 centres treated with photons and 9/51 with protons. Distribution of manufacturers and imaging modalities are shown in figure 1a-b . kV CBCT was the most used imaging modality. Technical settings for brain/head and abdomen sites were reported by 29 and 30 centres respectively. 10 centres reported multiple CBCT protocols per site, with protocols adapted based on various factors (e.g. age, weight, treatment modality and body size ). In total, 48 brain/head protocols and 51 abdomen protocols were reported. Technical CBCT settings are summarized in table 1 , with detailed distribution of kVp settings in figure 1c . Over 50% of the protocols used daily CBCT ( figure 1d ). Strategies aiming to reduce dose were reported by 34/51 centres for brain/head sites and 30/51 for abdominal sites. The most common strategies for both sites were to reduce exposure settings (brain/head: 15/51 and abdominal: 20/51) followed by avoiding CBCT (brain/head: 7/51 and abdominal: 4/51). Limitations to implementing CBCT were reported by 34/51 centres. 8/51 reported “No limitations”, other limitations included: “Lack of paediatric equipment or protocols” (7/51), “Image quality” (5/51), “Longer treatment time” (3/51), “No CBCT available” (3/51), “Patient compliance” (2/51) and “Higher dose” (1/51).

Conclusion Our survey reports the first comprehensive evaluation of paediatric CBCT protocols in European centres. Although CBCT is widely used and often used daily, we found great variability in the technical acquisition parameters, suggesting an unmet need for optimising paediatric IGRT protocols. We report a lack of consensus on how protocols are differentiated (e.g., by age, body size etc.). This survey offers data to support standardisation of paediatric CBCT protocols in alignment with modern RT techniques. The survey was done on behalf of SIOPe Rad. Onc. Working Group.

OC-0124 Effect of Body Weight Changes on Thecal Sac Dose in Spine SBRT H. Truong 1 , R. Poldy 2 , G. McPherson 1 , B. Nguyen 1,3 , D. Hammill 4 , B. Quah 1,4,5 , F. Syed 1,4,5