ESTRO 2023 - Abstract Book

S282

Sunday 14 May 2023

ESTRO 2023

Considerable quantitative differences were seen in clinical practice across European proton therapy centers for the treatment of pediatric PF tumors. While most centers used three coplanar beams, the balance between target vs. spinal cord/brainstem dose was largely center-dependent. This was especially seen for the EP case, which had a higher prescription dose. MO-0381 (A)symptomatic MRI changes after proton therapy; the Dutch national cohort of pediatric CNS tumors J. Rutgers 1 , A. Bannink-Gawryszuk 2,1 , P. van Rossum 3 , M. Lequin 1,4 , J. Maduro 1,5 , H. van der Weide 1,5 , M. Heesters 1,5 , B. Hoeben 1,3 , A. van der Heide 1 , S. Plasschaert 1 , C. Gidding 1 , E. de Vos-Kerkhof 1 , L. Meijer 1 , J. van der Lugt 1 , A. Schouten- van Meeteren 1 , W. Matysiak 5 , E. Seravalli 3 , H. Langendijk 5 , E. Hoving 1 , G. Janssens 1,3 1 Princess Máxima Center for pediatric oncology, Pediatric oncology, Utrecht, The Netherlands; 2 University Medical Center Groningen, Radiation oncology, Groningen , The Netherlands; 3 University Medical Center Utrecht, Radiation oncology, Utrecht, The Netherlands; 4 University Medical Center Utrecht, Radiology, Utrecht, The Netherlands; 5 University Medical Center Groningen, Radiation oncology, Groningen, The Netherlands Purpose or Objective Imaging changes after proton therapy (PT) for CNS tumors, their clinical relevance and risk factors in children gained focus in literature. The aim of this study was to assess (a)symptomatic imaging changes after pencil beam scanning PT in the Dutch cohort of pediatric CNS tumors with a centralized follow-up. Materials and Methods From the 100 pediatric patients with a newly diagnosed CNS tumor receiving PT at the University Medical Center Groningen between 07-2018 and 07-2021, 78 patients were eligible for retrospective analysis. Reasons for excluding 22 patients were: no informed consent, re-irradiation or a combination of PT with >2 fractions of photon therapy. In line with international protocols, all clinical and radiological follow-up was performed on a regular basis at the Princess Màxima Center for Pediatric Oncology using uniform scan protocols. PT-related imaging changes were defined as new abnormal T2 signal with contrast enhancement on T1 (T1gd+) outside any potential macroscopic residual tumor, within the irradiated volume, and not suspicious for progressive disease. The relationship between imaging changes and clinical symptoms was discussed multidisciplinary with the treating neuro-oncologist/neurologist, two radiation oncologists and a (neuro)radiologist. Kaplan-Meier and Cox proportional hazard models were used to calculate the cumulative incidence rates of (a)symptomatic imaging changes, and to evaluate potentially associated factors such as: gender, age, tumor location, chemotherapy, hydrocephalus, number of neurosurgical procedures, and dose to the craniospinal axis. Results A total of 78 patients and 556 MRI-exams were analyzed. Median PT dose was 54.0 GyE (range: 24.0-60.0) at a median age of 7.3 years (range: 1.1-18.9) and median follow-up from end of PT of 23.6 months (IQR: 14.8-36.8). At 3, 6, 9 and 12 months from end of PT, the respective cumulative incidences of T1gd+ changes were 6%, 26%, 33%, and 33% while the prevalence rate at 3, 6, 9, 12, 15 and 18 months (from end of PT) was 7%, 28%, 25%, 24%, 17% and 10%. The cumulative incidence of symptomatic imaging changes at 3, 6, 9 and 12 months from end of PT was 1%, 10%, 13%, and 13%, respectively. Patient age ≥ 8 versus <8 years significantly decreased the risk of T1gd+ changes (HR 0.15, 95% CI: 0.05-0.45, p=<0.01) with a cumulative incidence at 12 months of 11% vs. 58%, respectively. Older patients ( ≥ 8 years) were less susceptible to symptomatic imaging changes (HR:0.12, 95% CI:0.01-0.93, p=0.04) having a cumulative incidence at 12 months of 3% vs. 22%. Conclusion The incidence of PT-related MRI changes, based on centralized and structured clinical and radiological follow-up data of children with a CNS tumor treated in the Netherlands, has demonstrated T1gd+ changes in one third of patients. An increased risk of symptomatic imaging changes appears to be present in younger children. MO-0382 Risk factors for enteral feeding in young head and neck cancer patients during proton beam therapy M. Li 1 , A. France 1 , P. Sitch 1 , L. Lee 1 , J. Price 1 , D. Saunders 1 , E. Smith 1 , D. Thomson 1 , N. Thorp 1,2 , S. Pan 1 1 The Christie NHS Foundation Trust, The Christie Proton Beam Therapy Centre, Manchester, United Kingdom; 2 The Clatterbridge Cancer Centre, Department of Oncology, Liverpool, United Kingdom Purpose or Objective Head and neck cancer patients undergoing definitive radiotherapy can experience severe toxicities requiring enteral feeding to optimise their nutrition. There is a paucity of data on which paediatric and TYA patients would benefit from prophylactic RIG placement versus reactive tube feeding. This study aimed to identify the risk factors for enteral feeding in paediatric and TYA head and neck (HN) cancer patients treated with proton beam therapy (PBT). Materials and Methods The records of HN cancer patients aged ≤ 25 years old who completed PBT at our single institution from 1 January 2019 to 31 December 2020 were retrospectively reviewed (n=56). Paediatric patients were defined as patients <16 years old at the commencement of treatment. Patients requiring enteral feeding at the commencement of PBT were excluded (n=12). The patient, tumour and treatment details were collected from the electronic records. Feeding tube status had been prospectively recorded during treatment reviews and at each follow-up. Exploratory analyses were conducted alongside t- tests and univariate logistic regression models, with significance assessed at the 5% level, and risk thresholds found using ROC analyses.

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