ESTRO 38 Abstract book

S1081 ESTRO 38

patients were screened to be treated with FB. One patient treated with FB was excluded for analysis because the breathing traces could not be recorded for the treatment fractions. For the patients treated with AVBF and with FB the displacement regularity was 0.27±0.09cm and 0.25±0.14cm and the period regularity was 1.4±1.0s and 0.9±0.3s, respectively (Figure 2).

reprojection captured by a CCD camera, which provide target position control during treatment delivery. Dose delivery is automatically enabled when the tracking point is within a predefined gating window. Results 8526 breath-holds were analyzed. The mean amplitude of the gating window referred to the baseline breathing curve was 16.36 mm (SD 6.57 mm) (95%-confidence interval: [7.81 – 31.11] mm). The mean standard deviation of breath-hold inside the gating window was 0.42 mm (95%-CI: [0.05 – 0.94] mm). The gating window height had a mean value of 3.24 mm (95%-CI: [0 – 5] mm). Conclusion The use of the Catalyst TM optical surface scanner enables stable and reliable breath-holds during radiotherapy for left-sided breast cancer the clinical routine. EP-1980 Randomised trial investigating breathing regularity: Audiovisual biofeedback vs free breathing E. Steiner 1 , K. Makhija 1 , R. O'Brien 1 , J. Wolf 2 , J. Ludbrook 2 , P. Greer 2 , P. Keall 1 1 The University of Sydney, Central Clinical School- ACRF Image X Institute, The University of Sydney, Australia ; 2 Calvary Mater Newcastle, Radiation Oncology, Newcastle, Australia Purpose or Objective Irregular breathing leads to artefacts in 4DCT imaging and uncertainties during radiotherapy delivery. We present the early results of the first multi-institutional, randomised trial to investigate if breathing regularity improves with audiovisual biofeedback (AVBF) breathing guidance for lung cancer patients. Material and Methods We report the data from the first eleven lung cancer patients recruited to the ethics-approved trial. Patients were randomised 2:1 to the intervention arm with AVBF screening or the free breathing (FB) control arm (Figure 1).

Overall the FB arm had lower regularity values indicative of more regular breathing, but no significant difference between AVBF and FB could be shown (displacement regularity: p=0.41, period regularity: p=0.15). Thus, our null hypothesis is not supported. Patient 1 treated with AVBF showed large variations in displacement and period regularity for different treatment fractions resulting from large changes in the daily performance. Patient 5’s large displacement regularity values resulted from a different breathing pattern during CT simulation compared to the treatment fractions. Conclusion At this stage, no difference in breathing regularity between AVBF and FB could be shown. Further investigations will be performed. EP-1981 Intrafractional baseline drift in SBRT of lung tumors J. García Ruiz-Zorrilla 1 , M.A. De la Casa de Julián 1 , O. Hernando Requejo 2 , P. García de Acilu Laa 1 , C. Rubio Rodriguez 2 , J. Martí Asenjo 1 , P. Fernández Letón 1 , D. Zucca Aparicio 1 , J.M. Pérez Moreno 1 , X. Chen 2 1 Hospital Universitario HM Sanchinarro, Radiofísica, Madrid, Spain ; 2 Hospital Universitario HM Sanchinarro, Oncología Radioterápica, Madrid, Spain Purpose or Objective To investigate the frequency and amplitude of baseline or drift of lung tumors treated with stereotactic body radiation therapy (SBRT) and ExacTrac Adaptive Gating® with intra-fractional IGRT.Methods and materials Material and Methods Forty one fractions of 12 patients with lung tumors were treated with SBRT using ExacTrac Adaptive Gating® in a Novalis® linac. This system uses external markers to monitor the respiratory cycle and internal fiducial markers to set up the patient and measure the movement of the tumor. The tumor position is measured intermittently during the treatment via stereoscopic x-ray images to compensate the baseline drift. Therefore, the accumulative changes in the couch position correspond to the baseline drift in the tumor motion. Results The average change in position of the treatment couch during the treatment time was -0.1 ± 0.8 mm (mean ± standard deviation), -0.1 ± 1.2 mm, and 0.2 ± 1.9 mm in the left-right (LR), antero-posterior (AP) and cranio- caudal (CC), directions respectively. Overall the baseline shift/drift occurs toward the cranial directions. The incidence of a baseline drift exceeding 1 mm was 43%, for the CC direction, within 15 minutes of the start of treatment, and 63% within 25 minutes. On the other hand, the incidence of a baseline drift exceeding 3 mm was 4% for the CC direction, within 15 minutes of the start of treatment, and 25% within 25 minutes.

Breathing motion was measured with the Real-time Position Management (RPM) system (Varian Medical Systems). An in-house developed AVBF system provided breathing guidance to patients. Patients with AVBF screening were treated with AVBF if the AVBF-guided breathing was more regular during the screening session, or FB otherwise. Breathing regularity was quantified by the displacement regularity and the period regularity (as defined in Venkat et al. 2008) between the average breathing motion during the CT simulation session and the breathing motion during each treatment fraction. We tested the hypothesis that AVBF improves breathing displacement regularity and period regularity compared to FB using a one-sided t-test. Results 8 patients were recruited into the intervention arm, 3 patients into the control arm. In the intervention arm 3 patients were screened to be treated with AVBF, 5