ESTRO 2021 Abstract Book

S141

ESTRO 2021

At 35 years from diagnosis, the cumulative incidence of cardiac arrhythmia was 1.4% (95% CI 1.1% - 1.6%). Mean RT doses ≥10 Gy to the whole heart and substructures were associated with an increased risk of arrhythmias ( Table 1 ). Low-dose RT (mean RT dose 5.0 – 9.9 Gy) to the RCA was associated with an increased risk of arrhythmia (relative rate (RR) 2.0 95% CI 1.0 – 4.1) compared to survivors who did not receive RT. Figure 1 shows the associated cumulative incidence by dose levels. Low dose RT to other substructures was not associated with an increased risk of arrhythmia.

Conclusion Low dose RT to the RCA increases risk for the development of cardiac arrhythmias. This is intriguing as blood supply to the sinoatrial and atrioventricular nodes commonly arise from the RCA. RT dose to the specific nodal structures was not included in this analysis but should be explored further. These data provide evidence of the importance of cardiac substructure dosimetry in predicting late cardiac disease. OC-0209 Radiation-induced cavernomas: investigating the role of MRI-SWI for screening and surveillance in long-term cancer survivors B. Campbell 1 , A. Lasocki 2 , M. Bressel 3 , S. Oon 2 , N. Goroncy 4 , J. Seymour 5 , M. Dwyer 1 , K. Wiltshire 1 , K. Mason 5 , D. Tange 6 , M. Xu 1 , G. Wheeler 1 1 Peter MacCallum Cancer Centre, Department of Radiation Oncology, Melbourne, Australia; 2 Peter MacCallum Cancer Centre, Department of Cancer Imaging, Melbourne, Australia; 3 Peter MacCallum Cancer Centre, Centre for Biostatistics and Clinical Trials, Peter MacCallum Cancer Centre, Australia; 4 Peter MacCallum Cancer Centre, Department of Cancer Nursing, Melbourne, Australia; 5 Peter MacCallum Cancer Centre and Royal Melbourne Hospital, Department of Haematology, Melbourne, Australia; 6 Peter MacCallum Cancer Centre, Department of Cancer Surgery, Melbourne, Australia Purpose or Objective Radiation-induced cavernomas (RIC) are common late sequelae of cerebral radiation therapy (CRT), however, their natural history is poorly described. We report the largest cohort of long-term cancer survivors with RIC, and the first series of long-term surveillance using modern magnetic resonance imaging (MRI) with highly sensitive susceptibility-weighted imaging (SWI). The objectives are to better characterise the natural history of RIC, and evaluate the impact of MRI-SWI for screening and surveillance in long-term cancer survivors with In this retrospective study, eligibility included long-term cancer survivors enrolled in the Late Effects Clinic, prior CRT (2010 or earlier), participation in MRI-SWI surveillance, and documented diagnoses of ≥1 RIC. MRI- SWI were centrally reviewed: number and size of RIC were reported on “Baseline” and last “Follow-up” MRI- SWI. Results Of 467 long-term survivors with prior CRT, 122 were diagnosed with RIC, 9 were excluded due unavailability of MRI-SWI for central review. The remaining 113 patients were eligible with ≥1 RIC seen on MRI-SWI. Median age at CRT was 9.3 years, median CRT dose was 50.4Gy. Median time from CRT to Baseline MRI-SWI was 17.9 prior exposure to CRT. Materials and Methods