ESTRO 38 Abstract book

S529 ESTRO 38

Results Our experiments show that posterior sensors on right and left lateral plates detect cranial roll (figure 2) with average sensitivity of 0.04 and 0.06 pF per degree, respectively. Posterior and anterior sensors on the superior plate detect cranial pitch (figure 2) with average sensitivity of 0.13 and 0.06 pF per degree, respectively. Conclusion We had previously shown (Sadeghi, Lincoln et al. 2018) the capability of this system to detect translation motion. The current results show potential for rotation detection with this technology by monitoring the cranium without the need for ionizing radiation or the use of skin as a surrogate.

[1]). To provide the sensitivity of FDC1004, the MPR121- based system would necessitate sensors with areas larger by a factor of six. In addition, larger sensors would have to be two times closer to the target in order to provide similar performance [1].

Conclusion These advances in CMS technology offer significant performance improvements in terms of sensitivity, detection precision, sensor size and the dynamic range relative to the system previously described [1], thus making it more attractive and practical for clinical use. References 1. P. Sadeghi et al 2018 Phys. Med. Biol. 63 165019 PO-0971 Capacitive monitoring system for intrafraction rotation detection during frameless radiosurgery P. Sadeghi 1 , O. Semeniuk 1 , R. James 1,2 1 Dalhousie University, Physics & Atmospheric Sciences, Halifax, Canada ; 2 Dalhousie University, Department of Radiation Oncology, Halifax, Canada Purpose or Objective This work presents a novel, non-ionizing technique for continuous intra-fraction patient position monitoring during stereotactic radiosurgery. The system provides real-time cranial positioning information without relying on surrogates such as skin. Material and Methods The system is comprised of an array of conductive sensors arranged around the cranium. Capacitance of the sensor array is monitored continuously. The system is unique in that it is not sensitive to the position of the thermoplastic mask but registers the motion of the cranium within. The system has been shown previously (Sadeghi, Lincoln et al. 2018) to demonstrate 0.1 mm sensitivity in detection of cranial translation, and in this work is assessed for rotation detection. A cranial phantom with a hollow space modelling the average human brain was 3D printed provided a signal for evaluation of the optimal sensor arrangement for rotation detection (figure 1). The brain cavity walls were covered with thin copper foil (0.025 mm thickness) to replicate the conductivity of human brain. The cranial phantom was attached to a hexapod stage capable of performing 6D motion with respect to any pre- defined origin in space. Three plates were arranged around the phantom at 1 cm distance in superior, left lateral, and right lateral directions. Each plate was comprised of three sensors, each made from 0.025 mm thick copper film on 3D printed PLA backing. The middle sensor was 2.7 cm in diameter, the anterior and posterior sensors (sensors 1 & 3) were half rims with inner and outer diameters of 9 cm and 12 cm, respectively (figure 1). Pitch and roll rotations were introduced as the phantom was rotated in 1 degree steps in both positive and negative directions. The axes and origin for head rotation were defined based on Fick convention (Kunin, Osaki et al. 2007). Sensitivity was defined as change in average signal per degree rotation. The range (noise band) was the difference between maximum and minimum data points under stationary conditions. When the sensitivity was higher than the noise band, the sensor was considered to be detecting the respective motion.

PO-0972 Intrafraction prostate motion effects with or without ERB in highly hypofractionated proton therapy L.G.M. Zwart 1,2 , C.L. Brouwer 1 , P. Klinker 1 , C.H. Slump 2 , K.K. Wang 3 , N. Vapiwala 4 , J.A. Langendijk 1 , S. Both 1 , S. Aluwini 1 1 University of Groningen- University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands ; 2 University of Twente, MIRA Institute for Biomedical Technology and Technical Medicine, Enschede, The Netherlands ; 3 Johns Hopkins University, Department of Radiation Oncology and Molecular Radiation Sciences, Baltimore, USA ; 4 University of Pennsylvania, Department of Radiation Oncology, Philadelphia, USA Purpose or Objective Pencil beam scanning (PBS) technology allows the use of superior beam properties of protons to potentially improve outcomes with extreme hypofractionated radiotherapy for prostate cancer (PCa) patients. One of the technical challenges is the increased sensitivity to range uncertainties and intrafraction prostate motion. We have evaluated the robustness of extreme hypofractionated PBS proton plans to intrafraction prostate motion with (wERB) and without endorectal balloon (nERB) in PCa patients. Material and Methods Intrafraction motion measurements were available from 59 patients treated in ≥30 fractions in the department of radiation oncology of the University of Pennsylvania. Motion was recorded in left, right, superior, inferior, anterior and posterior direction for up to 6 minutes using a real-time electromagnetic tracking system. Patients (five wERB and six nERB) with the largest magnitudes of