ESTRO 2022 - Abstract Book

S145

Abstract book

ESTRO 2022

treatment details, toxicity data and disease status at each follow-up were recorded and exploratory analysis undertaken. Toxicity was reported as per Common Terminology Criteria for Adverse Events, version 4.0. Results The median age was 13 years (range, 2-25). 14 patients had ES and 6 patients had RMS. 16 patients had non-metastatic disease, 4 patients had lung only metastases. The median primary tumour size at diagnosis was 303.3cc (range, 54.8- 1051.7). 11 patients had definitive PBT, 6 patients had pre-operative PBT and 3 patients had post-operative PBT. The median prescribed dose was 50.4Gy (range, 41.4-59.4), and all patients had concurrent SACT. The median follow-up time was 12.5 months (range, 4-28). All patients experienced grade 3/4 lymphopenia during their course of PBT. At completion of PBT, all patients had an acute skin reaction. Only 3 patients had acute/subacute grade 3 skin reactions, and there were no grade 4 skin reactions. The other common toxicities were grade 1/2 fatigue (7 patients), constipation (5 patients) and diarrhoea (3 patients). One patient had grade 3 fatigue and another patient had grade 3 anorexia. One patient had grade 1 dysuria at completion of treatment which resolved by 6 weeks after PBT. Another patient had grade 1 haematuria at 6 weeks after PBT, which resolved by 1 year after PBT. Two patients had grade 2 lymphoedema at 6 weeks and 1 year after PBT. Lymphoedema severity improved for one patient, and was stable for the other. An asymptomatic left-sided sacral insufficiency fracture was found on routine imaging for one of the 20 patients at 17 months after completion PBT. Six months later, the same patient had an asymptomatic benign 2cm lesion in the right ischium detected on imaging. Three out of 20 patients had disease progression. One patient with pelvic ES treated with definitive PBT had local progression of the primary tumour and lung metastases 3 months after completion of PBT. Two patients relapsed distally 9 months after completion of PBT. Conclusion PBT for paediatric and TYA patients with pelvic ES and RMS has acceptable acute toxicities and offers good local control rates consistent with existing literature. Further long term follow-up is required to assess late toxicities and outcomes. 1 The Royal Marsden NHS Foundation Trust, Radiotherapy, Sutton, United Kingdom; 2 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Radiotherapy, Sutton, United Kingdom Purpose or Objective Active Breathing Control (ABC) is a motion management strategy that facilitates reproducible inspiratory breath-hold for thoracic radiotherapy (RT) to reduce intra-fraction respiratory-related target and organ displacement. This has been shown to reduce radiation dose to organs at risk (OARs). Reduction of treatment-induced late toxicity is of especially high importance in children. However, there is little published literature on the feasibility of using ABC in younger patients. The purpose of this study was therefore to report our institutional experience of using ABC for paediatric and teenage patients. Materials and Methods Following institutional review board approval, all patients aged ≤ 18 years referred for thoracic RT using ABC at our centre from 2013 to 2021 were identified. Electronic patient and RT records were retrospectively reviewed to obtain information on diagnosis, RT dose and technique, OAR dosimetry, tolerability of ABC, post-treatment imaging and early toxicity rates. Descriptive statistics were used and patients grouped into those receiving mediastinal RT (e.g. lymphoma) and ipsilateral thoracic tumours, including hemithorax RT (e.g. sarcoma), for the reporting of OAR dosimetry. Results In total, 12 patients had thoracic RT with ABC; median age 15.5 yrs (range, 10-18 yrs). The diagnoses were as follows: 5 Hodgkin lymphoma, 1 mediastinal B cell lymphoma, 5 Ewing sarcoma and 1 rhabdomyosarcoma. All patients have managed to comply with ABC during planning and for the duration of RT: 11 patients have completed RT, and 1 patient is still undergoing RT. The most common RT technique used was VMAT (n=9) with the remainder treated using IMRT (n=1) or conformal RT (n=2). For mediastinal RT cases (n=6), median dose prescribed was 30.6Gy (range, 19.8-40Gy), median mean heart dose was 11.4Gy (range, 4.8-19.4Gy), median mean lung dose was 9.9Gy (range, 5.7-14.5Gy) and mean lung V20 was 8.3%. For ipsilateral RT cases, (n=6), median hemithorax and total doses to primary tumour were 18Gy (range, 15-20Gy) and 52.2Gy (range, 36-60Gy) respectively. Median mean heart dose was 19.5Gy (range, 10.6-33.2Gy) and median mean lung dose was 17.7Gy (range, 16.3-30.5Gy). Mean bilateral lung V20 was 39.6%. Median mean contralateral lung dose was 5.2Gy (range, 3.5-11.6Gy) and mean contralateral lung V20 was 5.7%. At 3 months, 4/11 patients had radiological changes consistent with radiation pneumonitis, but only 1 was symptomatic (CTCAE v4.0 grade 2). At a median follow up of 36 months, only 1 patient had symptomatic radiation pneumonitis having received further thoracic RT for relapse. Conclusion ABC is a feasible and well tolerated motion management technique for younger patients receiving thoracic RT, with children as young as 10 yrs able to comply. The use of ABC results in heart and lung doses which are comparable to similar data in adults and can facilitate RT for extensive thoracic sarcoma. PD-0169 Active breathing control for children and teenage patients receiving thoracic radiotherapy J. Gough 1 , S. Mowat 1 , K. Robinson 1 , L. Sellman 1 , M. Youings 1 , H. Mandeville 2

PD-0170 Breath-hold proton therapy for mediastinal lymphomas: the expected effect on cardiac toxicity