ESTRO 2021 Abstract Book

S140

ESTRO 2021

Conclusion The addition of pt-RT to ASCT for patients with relapsed or refractory HL achieves excellent 5-year OS and PFS rates. Limited relapsed disease, ≤3 nodal sites, CMR prior to ASCT and CMR following pt-RT predict for favourable prognosis. OC-0208 Cardiac substructure dosimetry and late cardiac arrhythmia in the Childhood Cancer Survivor Study J. Bates 1 , S. Shrestha 2 , Q. Liu 3 , S. Smith 2 , D. Mulrooney 4 , W. Leisenring 5 , T. Gibson 6 , L. Robison 4 , E. Chow 7 , K. Oeffinger 8 , G. Armstrong 4 , L. Constine 9 , B. Hoppe 10 , C. Lee 6 , Y. Yasui 4 , R. Howell 2 1 Emory University, Department of Radiation Oncology, Atlanta, USA; 2 MD Anderson Cancer Center, Department of Radiation Oncology, Houston, USA; 3 University of Alberta, Department of Public Health Sciences, Surrey, Canada; 4 St Jude Children's Research Hospital, Department of Epidemiology and Cancer Control, Memphis, USA; 5 Fred Hutchinson Cancer Research Center, Clinical Research Division, Seattle, USA; 6 National Institutes of Health, Division of Cancer Epidemiology and Genetics, Rockville, USA; 7 University of Washington, Department of Pediatric Oncology, Seattle, USA; 8 Duke University, Department of Medicine, Durham, USA; 9 University of Rochester, Department of Radiation Oncology, Rochester, USA; 10 Mayo Clinic - Jacksonville, Department of Radiation Oncology, Jacksonville, USA Purpose or Objective Increasing radiation (RT) doses to the entire heart increase the risk of cardiac arrhythmias in childhood cancer survivors. However, associations between RT doses to cardiac substructures and the risk of arrhythmia has been inadequately investigated. We evaluated the relationship between RT dose to the heart and risk of arrhythmia and evaluated the contribution of RT dose to the cardiac substructures to this risk. Materials and Methods We determined the cumulative incidence of CTCAE grade 3 – 5 (severe, life-threatening, or fatal) cardiac arrhythmias among 25,481 five-year cancer survivors diagnosed between 1970 to 1999 in the Childhood Cancer Survivor Study (CCSS). Median age was 6.1 years (range 0 – 20 years) at diagnosis and 29.8 years (range 5.6 – 65.9 years) at last follow-up. We reconstructed treatment fields for survivors treated with RT (n = 12,228) on an age-scaled phantom and estimated mean RT dose to the heart, four chambers, four valves, and major coronary arteries (left anterior descending, circumflex, left main, and right coronary (RCA)). Piecewise exponential models evaluated associations between mean RT substructure dose and arrhythmias, adjusted for demographic and treatment-related characteristics, including total anthracycline dose in doxorubicin equivalents. Each substructure was individually added to a model with mean whole heart RT dose and the fit was assessed via the likelihood-ratio test to ascertain which substructures improved prediction of arrhythmia beyond whole heart dose. Results