ESTRO 2020 Abstract Book

S195 ESTRO 2020

The measured RED compared to water is shown in table 1. With increasing energy, the relative electron density approaches that of water (less than nominal PMMA density, due to air infiltration during fabrication of the material). System Energy RED WOmed T-300 100 kVp, 6.3 mm 2.5 ± 0.1 Siemens SOMATOM CT 120 kVp 1.66 ± 0.03 TomoTherapy MVCT Approx. 3.5 MV 1.04 ± 0.03 Varian Clinac 6 MV 1.02 ± 0.08 Dose calculations assuming a water flap and a bone cement flap agreed with each other within uncertainties, outside the flap. For a 6 MV beam orthogonally incident on the slab geometry, dose differences of 7% were observed at the water-flap interfaces between simulations performed with bone cement and with cortical bone. Specifically, compared to actual bone, PMMA bone cement provides reduced back scatter (which would reduce scalp doses) and reduced attenuation (which would increase intracranial dose). Conclusion For treatments of targets near volumes of bone cement, significant dose errors of up to 7% may result where density overrides are not used in the treatment planning system. Since bone cement implants may be mistaken for bone flaps in CT images (and kV IGRT images), care must be taken when planning post- surgical radiotherapy treatments of tumour beds or the scalp, to identify whether bone cement has been used. PH-0364 CIED malfunctions during radiotherapy course: a prospective, multi-centre, in-vitro evaluation C.Rosa 1 ,M.D. Falco 1 , S. Andreoli 2 , A. Delana 3 , E. Bliakharskaia 4 , A. Barbareschi 5 , P. De Filippo 6 , C. Leidi 6 , M. Marini 7 , D. Genovesi 8 , E. Di Girolamo 9 1 "SS. Annunziata" Hospital, Radiation Oncology "G. D’Annunzio", Chieti, Italy ; 2 ASST “Papa Giovanni XXIII”, Medical Physics Unit, Bergamo, Italy ; 3 “S. Chiara” Hospital, Medical Physics Unit, Trento, Italy ; 4 University of L'Aquila, Clinical Medicine- Public Health- Life and Environmental Sciences, L'Aquila, Italy ; 5 Tor Vergata University, Medical Physics Unit, Rome, Italy ; 6 ASST “Papa Giovanni XXIII”, Electrophysiology Unit, Bergamo, Italy ; 7 “S. Chiara” Hospital, Cardiology Unit, Trento, Italy ; 8 “G. D’Annunzio” University, Radiation Oncology “SS. Annunziata” Hospital, Chieti, Italy ; 9 "SS. Annunziata" Hospital, Heart Department- Arrhythmology Unit, Chieti, Italy Purpose or Objective Radiotherapy (RT) on cardiac implantable electronic devices (CIEDs), both pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs), may affect transiently or permanentlynormal device function. To analyze CIED malfunctions by direct exposure to doses up to 10 Gy, 145 PMs and 65 ICDs from three different centres were evaluated. Material and Methods Three centers with different LINAC/TPS combinations were involved in the study. A Varian Trilogy with Eclipse TPS, an Elekta Synergy with Oncentra Masterplan TPS and an Elekta Precise with Pinnacle TPS, were considered. All centres used home-made water phantom (a standard 20x23 cm 2 basin filled with two liters of physiologic solution) in order to simulate a human-body-like environment.

All CIEDs had a baseline examination. Two planning CTs (one with two ICDs and two PMs, and one with four PMs) were performed. The CIEDs were placed at the center of a home-made water phantom. A 5 cm RW3 solid phantom (r=1.045 g/cm 3 ) provided the appropriate backscatter radiation. The CT image-sets were used to build the corresponding treatment plan. CIEDs were delineated as targets by a radiation oncologist and two equally weighted beams of 20x20 cm 2 field size (one in antero-posterior, and one in postero-anterior projection, respectively), with a 6 MV photon energy, were used. Dose prescription to the average target was 2, 5 or 10 Gy with a dose inhomogeneity in the DVH up to within ±16%, depending on TPS. Radio- opaque markers were used to obtain a correct phantom positioning in each RT session. 61wireless-enabled CIEDs were observed in a real-time session using manufacturer-specific programmers. All CIEDs were interrogated after exposure and monthly during a three-month follow-up. Results During RT course, most wireless-enabled CIEDs (88.5%) recorded electromagnetic interferences (EMI). 16 ICDs reported major EMI, with pacing inhibition and VT/VF detection. After exposure, no changes in device parameters or software errors were observed in 209 CIEDs (99.5%). A soft reset occurred in a PM (0.5% overall; 0.7% among PMs). Seven PMs(3.3% overall; 4.8% among PMs) reported battery issues. During the three-month follow- up, a soft reset was reported in one PM after a single exposure of 2Gy (0.5% overall; 0.7% among PMs). Abnormal battery drain was observed in 11 PMs (5.2% overall; 7.6% among PMs), and in a ICD (0.5% overall; 1.5% among ICDs). All events presented regardless of exposure dose while permanent damage occurred in only older devices (see Table 1).

Conclusion Recent CIEDs have shown to resist direct photon exposure up to 10Gy, and only EMI were observed. Permanent malfunctions occurred solely in less modern devices. PH-0365 Can a dual isocentre technique enable cervix treatments on the MR-Linac? R. Chuter 1,2 , A. Cree 1,2 , P. Whitehurst 1 , R. Hales 3 , A. McWilliam 1,2 1 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom ; 2 The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom ; 3 The Christie