ESTRO 2021 Abstract Book

S1447

ESTRO 2021

(NMSC) with interventional radiotherapy (IRT). This is particularly important for centres that calculate the treatment plans with the TG-43 protocol. Materials and Methods Ten patients with NMSC, were treated in our centre with 192 Ir high dose rate IRT (HDR-IRT). The simulation of these patients was performed using a 2 cm bolus put on top of the Freiburg Flap skin applicator (Elekta). Two treatment plans were performed for each patient: one with the bolus material assigned to be air and the other with the bolus assigned to be tissue. This was performed in order to avoid a second CT scan without the bolus to each patient. The two plans were therefore calculated with the TG-43 protocol and with the TG-186 model-based dose calculation algorithm (MBDCA) in use in our centre (Advanced Collapsed Cone Engine – ACE, Elekta Stockholm, Sweden). Results The dose differences in the target between the TG-43 and the TG-186 calculations were compared. When no bolus is used (i.e. bolus is assigned to be air), the differences in the CTV are up to 3% in the proximity of the target, whilst at distances bigger than 4 cm the differences are up to 8%. When the bolus is considered in the calculation, the dose differences between the two algorithms are minimized, varying from less than 1% close to the CTV to a maximum of 5% at the distance. The big differences at the distance are clinically neglectable because they correspond to very small absolute dose values. Conclusion The current study presented a comparison between the TG-43 and the TG-186 protocols for NMSC HDR-IRT treatments. The introduction of a 2 cm bolus was proved to be useful, lowering the dose differences from 3% to less than 1% in the target area. In conclusion, this study proves that for skin IRT treatments, the use of a 2 cm bolus is suggested when a MBDCA is not available or not usable for its longer calculation time. PO-1722 Real-Time observation of patients with wireless-enabled cardiac ICD during RT: are these safe? D. Fasciolo 1,2 , C. Rosa 3,1 , E. Di Girolamo 4 , D. Genovesi 1,3 , M.D. Falco 1 1 SS. Annunziata Hospital, Department of Radiation Oncology, Chieti, Italy; 2 G. D'Annunzio University , Department of Neuroscience Imaging and Clinical Sciences, Chieti, Italy; 3 G. D'Annunzio University, Department of Neuroscience Imaging and Clinical Sciences, Chieti, Italy; 4 SS. Annunziata Hospital, Heart Department, Arrhythmology Unit, Chieti, Italy Purpose or Objective Oncologic radiotherapy (RT) may affect normal function of pacemakers (PMs) or implantable cardioverter- defibrillators (ICDs), and these effects are unpredictable, depending on patient and device characteristics. Potentially life-threatening malfunctions may present in PM-dependent or ICD patients. To evaluate transient, electromagnetic-interferences (EMI)-related malfunctions during RT course, 12 patients fitted with either an ICD (9) or a PM (3) were referred for the study. Materials and Methods All patients had a baseline interrogation of their device to evaluate PM-dependency or the presence of antitackycardia therapies stored in the devices’ memories. The mean patient age was 74 years (range: 66-82 years). Patients histologies varied between prostate and rectal adenocarcinoma, Merkel cell Carcinoma of the left arm and squamous cell carcinoma of the oral cavity. Doses ranged between 55 Gy to 78 Gy (1.8 or 2 Gy/die). A simulation computed tomography was performed to build the corresponding treatment plan, and the patients were radiated by a 6-MV linear accelerator (600 MU/min). The effective dose received by the CIEDs was assessed by an in-vivo dosimetry. During first exposure, all the patients were observed in a real-time session using manufacturer specific programmers. Device function, such as pacing and sense issues, parameter settings, noise interferences, detections, was recorder by the video camera in the bunker throughout the entire radiation exposure. After RT courses, all patients received a complete telemetry follow-up of their During exposure, most devices reported some EMI-related malfunctions. On detail, four ICDs and two PMs recorded minor transient EMI not affecting normal device functions, whereas four ICDs reported EMI-related over-sense, pacing inhibition and VT/VF detections (Table 1). As this would have led to inappropriate shock delivery by the ICD, magnet application on the ICD site was necessary to disable antitackycardia therapies. Only one ICD and one PM reported no EMI-related transient malfunction, withstanding radiation exposure. At immediate post-exposure interrogation, the ICDs that recorded major real-time malfunctions reported multiple high-rate arrhythmia detections stored in the devices’ memories. device. Results