ESTRO 2022 - Abstract Book

S29

Abstract book

ESTRO 2022

Conclusion A method to perform real-time proton dose reconstruction for dynamic motion was developed and experimentally validated. It reproduced measured doses well offline. The dose reconstructions can be done online when live streaming of spot delivery and target motion becomes available.

MO-0055 Safe classification of patients with CIED prior to RT of naso-/oropharyn- and esophageal carcinoma

L. Blümlein 1 , B. Dobler 1 , O. Kölbl 2 , R. Ringler 3

1 University Hospital Regensburg, Radiotherapy - Medical Physics, Regensburg, Germany; 2 University Hospital Regensburg, Radiotherapy, Regensburg, Germany; 3 OTH Amberg-Weiden, Technical University of Applied Sciences, Medical Physics, Weiden i.d. Oberpfalz, Germany Purpose or Objective Guidelines such as DEGRO/DGK [1] or the Dutch guideline by Hurkmans et al. [2] classify patients with cardiac implantable electronic devices (CIED) into risk groups based on the dose to the CIED to avoid malfunctions due to ionizing radiation such as inadequate pulse delivery. If CIED is located outside the radiation field, dose calculation by treatment planning systems (TPS) is not sufficiently accurate for safe classification. In certain cases, a magnet is placed on the CIED for deactivation of antitachyarrhythmia (ATA) therapy during treatment. The magnet is not included in the treatment planning. This leads to further uncertainty in the dose determination at the CIED. Therefore, the dose to the CIED has to be monitored by in- vivo dosimetry during the first treatment. The aim of this study was to establish a strategy for accurate classification of patients with esophageal or naso- and oropharyngeal carcinoma into risk groups prior to first treatment. Materials and Methods A phantom was designed and manufactured for dose measurements at the implant by TLDs and Gafchromic films. For 14 patients with esophageal or naso- and oropharyngeal carcinoma, treatment planning was performed in the TPS Monaco (Elekta, Sweden) using VMAT technique. Dose distributions of all plans were calculated with and without a virtual magnet and compared. Measurements were performed with the magnet on the surface of the phantom to assess the influence of the magnet on the dose in the CIED. The measurements were compared to the dose calculated with and without magnet and statistically evaluated. Results The calculation without magnet in the TPS compared with the measurement with magnet on the surface showed a dose underestimation about 15 % on average. The comparison between calculated and measured dose with magnet on the surface showed that the CIED dose is underestimated by about 14 % on average. According to a confidence interval of 95 %, the true value is between 8 % and 20 % with a probability of 95 % in both cases. Conclusion To ensure a safe classification of patients into risk groups, the calculated dose in Monaco should be increased by 20 % for dose estimation prior to radiation therapy. For VMAT irradiations of patients with esophageal or oro-/nasopharyngeal carcinoma, for which direct irradiation of the CIED is avoided, placement of the magnet does not result in significant impact