Abstract Book

ESTRO 37

S515

PO-0945 Controlling motion in radiotherapy: rapid shallow ventilation for thoracic and abdominal targets N. West 1 , M. Parkes 2 , J. Prentis 3 , C. Snowden 3 , J. McKenna 1 , M. Iqbal 1 , C. Walker 1 1 Newcastle upon Tyne Hospitals Trust, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom 2 University of Birmingham, School of Sport Exercise & Rehabilitation Sciences, Birmingham, United Kingdom 3 Newcastle upon Tyne Hospitals Trust, Peri-operative & Critical Care, Newcastle Upon Tyne, United Kingdom Purpose or Objective In radiotherapy, accounting for respiratory motion increases the volume of normal tissues irradiated, increasing toxicity to normal healthy tissues, constraining the efficacy of the treatment. A number of strategies are used to mitigate respiratory motion, however all have associated technological challenges and pitfalls; unsuited to modern, complex high dose radiotherapy employing modulated dose rates, gantry speeds, and rapidly changing leaf speeds to generate sophisticated dose distributions. The purpose of this study was to assess the potential for rapid shallow non-invasive ventilation (rsNIV) for controlling internal respiratory motion for radiotherapy purposes. To our knowledge, this is the first study to fully evaluate internal anatomical motion using rsNIV to regularise and minimise respiratory variations over a period long enough to image and deliver complex high dose radiotherapy. Material and Methods Ten healthy volunteers (age range 21.7-53.9 years; mean 37.5 years; 6f/4m) were scanned on an MR scanner in 3 respiratory modes; normal breathing and 2 non–invasive mechanically ventilated frequencies of 20 and 25 breathes per minute using a non-invasive ventilator. Sagittal and coronal cinematic datasets (at 3 frames per second) were acquired to evaluate the resulting respiratory motions and repeat scans assessed reproducibility. Respiratory amplitudes were measured across the lung–diaphragm interface in both sagittal and coronal planes. Basic physiological parameters and subject experiences were recorded to quantify tolerability of the ventilation. Results Basic physiological observations and subject experience questionnaires demonstrated rsNIV to tolerable and comfortable. Motion analysis of the lung-diaphragm interface in the sagittal (figure 1) and coronal planes demonstrated that mean respiratory amplitude reduced considerably (55-64% reduction: dependent on the point across the interface) using rsNIV compared to subject initiated normal respiration.

More advanced image analysis demonstrated there is also benefit to inferior anatomy with considerable motion reductions observed in the abdomen using rsNIV. Conclusion For the first time, simple, comfortable ventilator controlled rapid shallow respiration has reported large reductions in internal thoracic and abdominal motions. The clinical application of such large respiratory motion reductions could be profound. Facilitating reduced motion would allow improved dose distributions, dose escalation and increased treatment efficacy. This is important for lung cancer patients where local control is limited by normal tissue toxicity. Similarly, this study demonstrated benefits exist for other tumour sites such as breast, liver and pancreas where respiratory motion also impacts on target definition and dose distributions. This work is being extended to patients referred for hypofractionated thoracic radiotherapy. PO-0946 Breath-hold motion effect in pencil beam scanned proton therapy for lung cancer – experimental study J. Gorgisyan 1 , A.J. Lomax 1 , P. Munck af Rosenschold 2 , G.F. Persson 3 , J. Scherman Rydhög 2 , F. Gagnon-Moisan 1 , M. Egloff 1 , G. Fattori 1 , S.A. Engelholm 3 , D.C. Weber 1 , R. Perrin 1 1 Paul Scherrer Institute, Center for Proton Therapy, Villigen PSI, Switzerland 2 Skane University Hospital, Department of Radiation Physics, Lund, Sweden 3 Rigshospitalet, Department of Oncology, Copenhagen, Denmark Purpose or Objective Breathing motion during proton therapy may inc rease the treatment uncertainties. The breath-hold motion management technique can possibly mitigate such uncertainties. The aim of this study was to experimentally investigate the dosimetric effect of the breath-hold stability using fluoroscopy data from patients and a 4D breathing phantom. Material and Methods Dataset of three locally-advanced lung cancer patients (Cases A, B and C), previously treated with photon radiation therapy, was considered for this experimental study. The tumors’ geometrical models were segmented on breath-hold CT images and subsequently 3D-printed to serve as holders for radio-chromic films using an anthropomorphic breathing phantom. The phantom was setup to replicate the patient motion extracted from fluoroscopy imaging of repeated breath-holds and free- breathing. Single field uniform dose (SFUD) and intensity- modulated proton therapy (IMPT) plans were delivered

Measured respiratory motion of the lung-diaphragm interface in the sagittal plane are displayed in figure 2.