ESTRO 2023 - Abstract Book

S245

Saturday 13 May

ESTRO 2023

mean deviation per treatment site (12 measurements) to the original model by Caprioli et al. The resulting deviations from the fading model were extracted by calculating the residual RMSE. Results A total of 36 measurements were collected from three sites, which had different linacs and used different field sizes as indicated in table 1. All sites used a 6MV photon beam and scanned the films at a resolution of 100x100 µ m ² . Following normalizations were required: +3.6%, -9.2% and +10.6%. Figure 1 shows the data after normalization. The median dose difference was 0.33 % (range: -2.1% to 4.7%). 75% of the validation measurements (27/36) were within 2% of the fading surface.

Conclusion The linear fading model of Caprioli et al. accurately models the fading behaviour of the BaFBr:Eu2+ OSL-type dosimeter. Due to the sensitivity of the OSL signal to the field size, film production, energy spectrum and scanner settings a normalization was required per centre. A site specific signal-to-dose calibration protocol will therefore be required. MO-0310 In-vitro effects of relevant clinical radiotherapy regimes on Cardiac Implanted Electrical Devices S. Manley 1,2 , A. Fenwick 3 , M. Fraser 3 , M. Lowrey 3 , N. West 2 1 The James Cook University Hospital, Radiotherapy, Middlesbrough, United Kingdom; 2 The Freeman Hospital, Northern Centre for Cancer Care, Newcastle-upon-Tyne, United Kingdom; 3 The Freeman Hospital, Cardiac Rhythm Management, Newcastle-upon-Tyne, United Kingdom Purpose or Objective Quantify the effects of clinically relevant (6X and 10FFF) radiotherapy to Cardiac Implanted Electrical Devices (CIEDs). International guidelines for radiotherapy of patients with a CIED, have been developed over the past four decades, however, the current data set contains results from situations which may be less relevant with modern devices. Newer technology has improved electronic filtering which prevents both inappropriate pacing inhibition and increased current drain, preserving battery life. There is a lack of data for effects on modern devices from modern techniques such as hypofractionation and FFF beams. Data were sought on a clinically relevant change of >25% from the set pacing voltage, or inappropriate defibrillation shock. Current international guidelines advise limiting the energy to <10MV and the total treatment dose to no more than 5Gy to any CIED Materials and Methods A total of 160 explanted CIEDs with remaining battery >1 - 15 years (median 8.5), were set to output a fixed, clinically relevant pacing signal. The devices were exposed to either 6, or 10MV radiotherapy beams from a Varian TrueBeam LINAC at our centre. CIEDs were irradiated in both normal operating conditions having set the sensitivity to a maximal uniform voltage of >1mV; and in MRI-conditional / Asynchronous mode, with pace sensing turned off. Devices were split by manufacturer, randomised, then exposed to either 6X or 10FFF regimes with pacing data recorded via PicoScope.

Results