ESTRO 37 Abstract book

ESTRO 37

S457

1 Klinikum rechts der Isar- Technical University of Munich TUM, Department of Radiation Oncology and Radiotherapy, Munich, Germany 2 Klinikum rechts der Isar- Technical University of Munich TUM, Department of Cardiology, Munich, Germany 3 Klinikum Garmisch-Partenkirchen, Zentrum Innere Medizin, Garmisch-Partenkirchen, Germany Purpose or Objective Incidences of both cardiac implantable electronic devices (CIED) and malignant tumours are rising, likewise the number of patients undergoing RT while having CIED increases. The German Society for Radiation Oncology (DEGRO) proposed a national guideline to standardize safety measures and documentation of CIED patients undergoing radiotherapeutic treatment (RT). Aim of this work is a detailed analysis of malfunctions and technical alterations in CIED patients treated at our clinic with a special focus on the putative influence of dosimetric parameters Material and Methods We evaluated 56 patients (median age 74 years, range 51-89 years) with 58 RT courses treated at our department and evaluated the dose statistics for the device as well as the beam energy. Irradiation mostly took place in the thoracic (29.3%), pelvic (25.9%) and the head region (22.4%). A total of 79.3% of all patients had implanted a pacemaker (PM) and 20.3% an implantable cardioverter defibrillator (ICD). Irradiation technique consisted mainly of 3D planning (29.3%), rapid arc (29.3%), opposing-field irradiation (12.1%) and Tomotherapy (10.3%). We also collected CIED interrogation data (battery status, intrinsic signal amplitude, pacing impedance, pacing threshold) before and after RT treatment (median number of interrogations was 3, range 1-22) and information about any CIED malfunction. Overall 32,1% of patients were device dependent. Results Off all treatments, 18 received a measurable dose at the device (median dose of patients with thoracic irradiation: 0.62 Gy, range 0.05-5.3 Gy). Following the risk stratification of the DEGRO guideline 62.1% of the treatments were at low risk 34.5% at intermediate risk and 3.4% at high risk. Two CIEDs (3.4%) showed a malfunction (device reset to backup pacing mode, electric restart of device) during RT, however no clinically relevant complication was reported. Both cases underwent thoracic RT (esophageal cancer) with a beam energy of 10 and 15 MV and were classified as low and intermediate risk. CIED data analysis showed no significant parameter changes during RT treatment overall, but high variation of differences in ventricular pacing impedance. Conclusion In the observed patient group RT doesn’t seem to exert short-term effects on sensing and pacing function or lead impedance. Device malfunction occurred rarely and only at higher beam energies, however with no life- threatening outcome. Regarding procedure standardization switching focus from cumulative dose at the device to beam energy could be considered.

1 Medizinische Universität Wien, Department of Radiotherapy, Vienna, Austria 2 Medical University of Vienna, Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria 3 Faculty of Medicine Ramathibodi Hospital, Department of Diagnostic and Therapeutic Radiology, Bangkok, Thailand 4 EBG MedAustron GmbH, Medical Physics, Wiener Neustadt, Austria Purpose or Objective Recently, a new type of radiochromic film, the EBT-XD film, has been introduced for high dose radiotherapy. This film is comparable to the well described EBT3 film but has a slightly different composition and a smaller active layer. This study benchmarks the EBT-XD against the EBT3 film for photon beams (6 and 10 MV) and proton beams (97.4 and 148.2 MeV). Material and Methods For both film types film reading characteristics, such as post irradiation darkening, film orientation effect and lateral response artifact (LRA) were investigated. Dosimetric characterization of the different film types was performed in photon and proton beams regarding film sensitivity, energy and beam quality dependency. For proton irradiations the quenching effect was studied in a single Bragg peak and subsequently compared. These experiments were performed for a nominal proton energy of 97.4 MeV and a dose in the entrance region of 2 Gy. Furthermore, films were evaluated regarding their performance measuring dose values in a spread-out Bragg peak (SOBP). The SOBP was 8 cm long with energies varying between 140.3–186.8 MeV. Results EBT-XD films showed the same characteristic on film darkening as EBT3. The orientation effect was reduced by 3.1% for EBT-XD compared to EBT 3 (at 20 Gy). Also, the LRA was found to be reduced for EBT-XD films for all investigated dose levels (i.e. up to 40 Gy). For 2 Gy the difference between center and off-axis position (i.e. 8 cm) was 5% for EBT3 and 2% for EBT-XD. The dose response curves, which were evaluated for each RGB channel, showed a superiority of EBT-XD over EBT3 films for doses higher than 5 Gy (red channel evaluation). For this dose region a green channel evaluation of the EBT3 films yielded a similar response as the red channel evaluation of EBT-XD films. An advantage of green channel evaluation for higher doses, as reported in literature for EBT3 films, was not observed for EBT-XD films (cf. Fig 1). The maximum calibration curve difference caused by varying beam energies was 1.8% for EBT-XD films (for photon and proton beams). In comparison, EBT3 films showed energy dependent differences of 3.2% (photon) and 4.6% (proton). A quenching effect of up to 10% was found for both film types for a proton beam of 97.4 MeV. Along the beam axis of an SOBP EBT3 and EBT-XD showed a similar response. At mid position of the SOBP both film types underestimated the dose by 2.8%. This value increased towards the distal edge of the SOBP to 8.7% (EBT-XD) and

Poster: Physics track: Basic dosimetry and phantom and detector development

6.1%

(EBT3)

(cf.

Fig.2).

PO-0870 Characteristic of EBT-XD versus EBT3 radiochromic films for dosimetry in photon and proton beams P. Kuess 1,2 , S. Khachonkham 1,2,3 , R. Dreindl 4 , G. Heilemann 1,2 , W. Lechner 1,2 , H. Fuchs 1,2 , D. Georg 1,2