ESTRO 2021 Abstract Book

S1500

ESTRO 2021

PO-1772 SGRT monitored deep inspiration breath-hold using oxygen enriched air M. Ramtohul 1 , S. Parveen 1 , B. Allan 2 , A. Qudir 2 , S. Green 1 , Q. Ghafoor 2 , M. Parkes 3

1 University Hospitals Birmingham, Radiotherapy Physics, Birmingham, United Kingdom; 2 University Hospitals Birmingham, Radiotherapy, Birmingham, United Kingdom; 3 Amsterdam UMC, Department of Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Radiotherapy treatments for left-sided breast cancer in deep inspiration breath hold are in common use for reducing heart toxicities. It is known that oxygenation can increase the length of breath-hold. The Venturi mask provides a cheap way of giving up to 60% oxygen enriched air to patients using the piped oxygen supplies to the radiotherapy bunkers. In addition, radiotherapy treatments require position to be maintained during treatment. This study used 10 healthy volunteers to compare the breath-holds in air against breath-hold using 60% oxygen and the Venturi mask in the treatment position. The proportion of time in which the volunteers remained in a treatable position was also looked at. Materials and Methods Ten healthy volunteers were asked to perform breath-holds in the standard treatment position for patients with breast cancer using the breast board. Volunteers were asked to hold their breath and this was monitored using an AlignRT SGRT system. This was then repeated after the volunteer had rested and breathed oxygen enriched air supplied by the Venturi mask system. No extensive breath-hold training was performed. The data acquired from AlignRT was analysed to determine the length of breath-hold and movement during breath- hold. Results Using the recorded vertical positions (anterior-posterior motion), the average breath-hold in air for the volunteers was 102±43 seconds, while using the Venturi mask an average breath-hold of 202±80 seconds almost double to that acquire in air. The breath-holds could also be detected through the recorded longitudinal positions (superior-inferior motion) and pitch (angular motion in the anterior-superior plane). Considering a movement tolerance of 3mm in the vertical direction after start of breath-hold, treatment would terminate after 62±27 seconds when breathing in air while it would terminate after 88±78 seconds when breathing 60% Oxygen. This reduces the usable treatment time for an air breath-hold by 39% and by 44% for the oxygen enriched air. Overall a 42% = 26 seconds increase in usable breath-hold for treatment is achieved by using oxygen enriched air. Conclusion The duration of deep inspiration breath-hold can be extended using 60% Oxygen enriched air with a Venturi mask. The duration of breath-hold could be doubled, but this is dependent on maintaining position. Further work will establish whether giving the subject feedback on their external position will increase the usable treatment time and therefore maximise the benefit of using oxygen enriched air to prolong breath-hold duration. PO-1773 Value of respiratory monitoring and analysis for patients irradiated for lung or breast carcinoma E. van Dieren 1 , D. Hubers 2 , D. Woutersen 1 , K. Slump 3 1 Medisch Spectrum Twente, Radiotherapy, Enschede, The Netherlands; 2 University of Twente, Faculty of Technical Medicine, Enschede, The Netherlands; 3 University of Twente, Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS), Robotics and Mechatronics (RAM), Enschede, The Netherlands Purpose or Objective Thoracal tumors move during radiotherapy. Hence, planning CT is usually performed with respiratory monitoring, such as the chest wall motion detection system RGSC (Varian, Palo Alto, USA). However, motion may change, and 4D CBCT may not always be feasible. This study investigates the potential of using RGSC data to detect changes in respiratory motion. Materials and Methods The retrospective study investigated data from 28 patients treated for lung cancer patients (30*2 Gy), and 8 patients treated using Deep Inspiration Breath Hold (DIBH) for breast cancer (16*2.67Gy). For lung cancer patients, RGSC data per session were analyzed in terms of (variance in) amplitude and frequency. Variances were compared between fractions and to plan scan. Results were correlated with patients characteristics (age, gender, weight, COPH, asthma). For breast cancer patients, where DIBH was performed with visual feedback, window of +/- 5 mm. and automated beam hold, RGSC data were analyzed in terms of DIBH level variations between treatments. In addition, number of treatment interrupts and recovery to the original DIBH level afterwards were assessed. Results Most lung cancer patients ( 2 / 3 ) have little variance, but sometimes variance is quite large (fig1). Plan scan frequency and amplitude variance correlate (0.91). Variance in session amplitude and frequency correlate better with plan scan amplitude variance (0.82 and 0.73 resp.), than variance in plan scan frequency does (0.52 and 0.11). Patient characteristics do not predict session variance. For one session of the last patient (28, session 6), a 4CBCT was available. Variances of this patient were low. Session variances were lower than those of plan CT. In addition PTV movement during the session was within boundaries of those in planCT. For breast cancer patients, DIBH level was 11.4-16.2 mm for the group (fig1). DIBH variations between sessions are 1.3-2.6 mm, which will probably not have a large effect on lung and heart dose. For 1 patient, interrupts occurred every session. For 2 patients, treatment interrupt occurred less but breath hold level, still being within the DIBH window, was lower after continuation. Since original DIBH level is used to setup and planning, CTV2PTV margin near the lung may be slightly less.