SP-0204: Online MRI guided 4D-SBRT of thoracic and abdominal tumours

ESTRO 33, 2014 treatment position. Furthermore, a hardware system is currently tested that allows to image patients with RTpositioning aids in the PET/MR scanner to acquire functional PET/MR data in treatment position. In a last part of the talk, potential fields of dedicated use of PET/MR data for improved RT treatment planning will be discussed. A first step towards individualized RTplanning is improved target volume delineation by additional information from functional imaging with PET/MR. Moreover combined PET/MR imaging could in the future also serve as a powerful tool for multiparametric assessment of biological parameters of tumors, such as tumor hypoxia. Hence, PET/MR data may in the future be used as a basis for biologically individualized RT treatment planning, as e.g. dose painting. As a consequence, combined PET/MR imaging offers different possibilities to improve RT treatment planning and application and may be a prerequisite for multiparametric biologically individualized RT in the future. SP-0204 Online MRI guided 4D-SBRT of thoracic and abdominal tumours G.J. Meijer1, C.A.T. Berg1, B.W. Raaymakers1, M. Van Vulpen1, J.J. Lagendijk1 1 UMC Utrecht, Department of Radiotherapy, Utrecht, The Netherlands In radical cancer treatments, external beam radiotherapy has the advantage over surgical interventions that it is non-invasive. However on the downside, the non-invasive nature directly implies that we don’t have (eye)sight at our target area and surrounding healthy anatomy during treatment. Especially in the thoracic and abdominal region dayto-day anatomy changes that go hand in hand with respiratory tumour and organ movement limit high dose deliveries within the conventional multi-step radiotherapy chain. As such, independent groups all over the globe are pioneering narrowing the bridge between planning and delivery by somehow integrating MR imaging within or just prior to dose delivery. In our institution the building of the 2nd prototype of our MR-linac was recently completed. This system combines a 6MV linear accelerator mounted on a gantry with a 1.5T MR scanner and allows onsite MR image acquisition with simultaneous dose delivery. MRI has been proven to be an extremely versatile imaging technique in three ways. Firstly, due to its high soft tissue contrast in combination with novel advanced cardiac and respiratory gated sequences high quality images can be created for tumour definition in a moving geometry. Secondly, MRI is flexible in acquiring dynamic images at various temporal resolutions. Using respiratory binning techniques 4D-MRI scans can be obtained (similar to 4D-CT, where the 4th dimension is phase). But at frequencies of typically 2 Hz 2D cine-MRI images can be acquired that allow real-time tracking of a tumour/organ in any desired plane using optical flow techniques. At millisecond resolution 1D scans (navigators) can be obtained to track a specific anatomical interface in any arbitrary direction. Thirdly, special sequences (e.g. diffusion weighted imaging [DWI] and dynamic contrast enhancement [DCE]) can be used to characterize tissue properties. These techniques have proven to be useful in identifying high-risk volumes in multiple tumour sites and therefore can be used as an input for dose painted treatment strategies. The synergies of the above listed merits come particularly into play in the complex local regional treatment of invasive thoracic and abdominal tumours embedded in a moving and vulnerable anatomy. For example, current adjuvant and definitive oesophageal cancer radiotherapy is far from optimal: large volumes involving both macroscopic and microscopic spread are irradiated to homogeneous dose levels confined by the tolerances of the surrounding healthy tissues. Incorporating the above listed features with clever systems capable of real-time plan adaptation will allow dynamic tailoring of dose gradients by continuously balancing tumour control versus organ sparing. Similarly, contemporary radiotherapy outcome for pancreatic cancers is disappointing, partly due to the aggressive nature of the disease but also due the current technical limitations. Present CT-based target definition is at least suboptimal and image guidance techniques that precisely assess the tumour interface with the surrounding duodenum or vascular structures are absent. As a consequence, potential curative dose levels cannot be obtained. Supplementary MR imaging during work-up and online 4D MR guidance techniques might enable safe irradiation with tumour ablating dose levels. In general, seamless MRI guided integration of 4D target definition, 4D treatment planning and 4D dose delivery with real-time feedback loops within one procedure will generate great potential for stretching the therapeutic frontiers of current radiotherapy applications in the domain of thoracic and abdominal oncology.

S81 SP-0205 Monoenergetic synchrotron beams: first human experience for therapeutic purpose J. Balosso1, F. Estève2, H. Elleaume3, A. Bravin4, J.F. Adam5, M. Renier4, C. Nemoz4, T. Brochard4, P. Berkvens6, J.F. Le Bas7 1 University Joseph Fourier, Radiation Oncology, Grenoble, France University Joseph Fourier, Grenoble Institute of Neurosciences, Grenoble, France 3 Inserm U836 E6, Grenoble Institute of Neurosciences, Grenoble, France 4 ESRF, Biomedical line ID17, Grenoble, France 5 University Joseph Fourier, Physics, Grenoble, France 6 ESRF, Radioprotection, Grenoble, France 7 University Joseph Fourier, Neuroradiology, Grenoble, France Synchrotron radiation (SR) at the ESRF has several notable features for medical use: a fluence5 to 6 orders of magnitude higher than that of a conventional X-ray tube, abroad spectrum extending up to more than 300 keV and a very small divergence(<0.1º). These features allow to develop two types of approaches for therapeutic purposes: i) irradiations of tissues using polyenergetic arrays of high dose rate microbeams i) fast irradiations of tumours using monochromatic X-rays in the energy range dominated by the photo-electric effect on heavy compounds previously introduced in the target volume. This second method operated as Stereotactic Synchrotron Radiation Therapy (SSRT) will be discussed in this presentation. Heavy atoms introduced in the tumor increase the probability of interaction with X-rays. Furthermore,the monochromatic synchrotron radiation can generate photoelectrons that deposit dose in the close vicinity of these atoms. The heavier the atoms, the higher the maximum energy of photoelectric activation (k-shell). Consequently, the radiation becomes more penetrating (by localized dose enhancements), and hence interesting, for treating deep-seated tumours. Thus energies above 79 keV stimulates the platinum k-shell and 33.2 keV that of iodine. Higher energies (80-100 keV)allow setting movements to photo electrons with moderate kinetic energy depositing much energy over a very small distance. The resulting energy deposition immediately adjacent to the heavy atoms becomes significantly greater than theX-ray energy deposition in surrounding healthy tissues, where Compton scattering predominates. The objective of SSRT is therefore to load the therapeutic target with heavy atoms and to treat it with synchrotron beam of energy adapted to the nature of the atoms. Preclinical experience carried out since a decade on the biomedical beam line ID17 at the ESRF focused on the use of radiological iodinated contrast agents or with platinum compounds provided as cisplatin or carboplatin, which are commonly, used anticancer agents. The future possibility to use nanoparticles (Gd, Au) is presently being investigated in preclinical developments. The first clinical study of therapeutic application of synchrotron radiation is underway since June 2012 at the ESRF and at the University Hospital (CHU) in Grenoble (France). A particular treatment room has been built in the main experimental room of ID17 (see figure).

The patient is seating on an armchair with his head maintained fixed in a tight mold supported by the same stereotactic frame used at the CHU Radiotherapy department for the complementary irradiation. At the end of 2013, this study has already included six patients suffering from few brain metastases of medium-to-small volume; all patients were in good general condition. The treatment procedure at the ESRF includes the administration of a highly iodinated iso-osmolar contrast agent (400 mg/ml nominal concentration) followed by the monochromatic irradiation in the next minutes, in 4 to 10 orientations. In this first clinical trial phase, the patients receive a fraction of the treatment by SSRT while the complement of the treatment is delivered by standard