Effect of Radiotherapy on ATTR Cardiac Amyloidosis : a Proof of Concept Study

Inclusion Criteria: * Age \>65 y.o. * Dyspnoea on exertion (NYHA II or more). * Stable elevated cardiac enzymes (ultra sensitive Troponin T \> 14 ng/L on consecutive sampling or BNP \> 100pg/mL) * A positive 99mTc-DPD cardiac scintigraphy (Grade 2 and 3) suggesting an ATTR or wt amyloidosis. * Additional imaging also compatible with cardiac amyloidosis (cardiac ultrasound showing basal to apical longitudinal strain gradient and magnetic resonance imaging with elevated T1 value or extracellular volume). * Compliance with the informed consent as attested by its signature. * Positive baseline 18F-Florbetapir imaging, as assessed visually and quantitatively by a Tissue to Background Ratio \> 1.45 Exclusion Criteria: * Positive serum protein immunoelectrophoresis with monoclonal gammapathy. * Previous external beam radiotherapy including the chest. * Claustrophobia * Presence of internal non-MR compatible devices * Creatinine glomerular filtration rate \< 30 ml/min * Oncologic disease (excluding skin cancer) active or in remission from less than 5 years