ESTRO 36 Abstract Book

S215 ESTRO 36 _______________________________________________________________________________________________

K. Brock 1 1 MD Anderson Cancer Center, Imaging Physics, Houston, USA Image registration is challenging in simple cases of deformable tissues. In the presence of anatomical and functional changes, these challenges can substantially increase. This presentation will evaluate the translation of standard deformable image registration techniques to challenging cases of anatomical and function response. Limitations of the techniques in the adaptive scenario will be discussed and validation techniques will be described. Although all registration techniques have uncertainties, once understood and quantified, the clinical application of these registration techniques can often improve the treatment in the adaptive radiotherapy treatment paradigm. One of the primary uses of deformable image registration for adaptive radiotherapy is dose accumulation, including the accumulation of dose assessed on each treatment fraction as well as the propagation of the initially planned dose onto the adaptive or replanning image. This process generates a wealth of data that can overwhelm a clinical process. Strategies will be discussed for distilling this data down into meaningful data that can be clinically evaluated. This presentation will also illustrate dose accumulation workflows that are clinically feasible as well as the use of deformable registration for dose propagation between an initial and adaptive planning image. Objectives for this presentation include: 1. Describing techniques and limitations of image registration in the presence of anatomical and functional changes 2. Addressing the question: how accurate is accurate enough for clinical use 3. Illustrating a workflow for dose accumulation that is clinically feasible 4. Strategies for reporting dose accumulation results SP-0405 Adaptive strategies to account for anatomical changes J.J. Sonke 1 Geometric uncertainties limit the precision and accuracy of radiotherapy. In room imaging techniques are now readily available to reimage the patient prior to and during treatment. Typically, these images are used to reposition the patient and thus minimize target misalignment. Anatomical changes, however, frequently occur during treatment but cannot be accurately corrected for using a couch shift. Adaptive radiotherapy, on the other hand, utilizes an imaging based feedback loop to adjust the treatment plan and thus has to potential to account for such anatomical changes. In this presentation, the magnitude and frequency of anatomical changes will be exemplified and various adaptive protocols will be described. Finally, current challenges and future perspective of adaptive strategies to account for anatomical changes will be discussed. SP-0406 Adaptive strategies to account for functional changes I. Toma-Dasu 1 1 Karolinska Institutet, Medical Radiation Physics, Stockholm, Sweden The progress and technological development of functional and molecular techniques for imaging tumours has offered the possibility of redefining the target in radiation therapy and devising the treatment in an innovative manner accounting for relevant biological information on metabolic, biochemical and physiological factors known to 1 Netherlands Cancer Institute, Radiotherapy department, Amsterdam, The Netherlands

used in nuclear medicine, and as will be described in this talk, also to provide a novel method to monitor external- beam RT. CLI is becoming a well-established method for preclinical in vivo small animal optical imaging and has been also applied to humans for example to image a patient treated with 131-I [2]. A very recent approach is the use of CLI for the analysis of ex vivo fresh tumor specimens removed during neurosurgery [3]. From the radiotherapy side there has been considerable interest in the possible use of CLI to monitor external- beam radiation therapy. The main dosimetric parameters that could be measured are the percent depth dose (PDD) and the lateral dose profile of the radiation beam. It has been hypothesized that these parameters can be directly measured by imaging the CR induced in a water phantom as a surrogate of the dose. In the literature it has been shown that due to the anisotropy of the CR emission some differences arise between the CR-derived and the true dose profiles, these differences in the PDD and lateral dose profile can be taken into account by using correction factors derived from Monte Carlo simulations [4]. A more practical approach to reduce the effect of Cerenkov emission anisotropy is adding a CR-excitable fluorophore to the water in the phantom, the addition of a fluorophore allows more accurate estimation of the PPD [5]. The use of CLI for real-time portal imaging during CyberKnife radiation therapy was also investigated by irradiating a water tank phantom. Imaging at 30 frames per second was acquired showing that CLI is a feasible tool to image dynamic and static objects [6]. An interesting development is the use of CR to visualize in real time the dose delivery during radiation therapy [7], more precisely it has been shown that it is possible to visualize the surface dose during the treatment. In conclusion, the use of CLI in the RT field could lead to a novel approaches to perform QA and real time in vivo dosimetry References [1] Jelley JV 1958 Cerenkov Radiation and Its Applications (London: Pergamon) [2] Spinelli, AE, Ferdeghini, M, Cavedon, C, Zivelonghi, E, Calandrino, R, Fenzi A. et al, First human Cerenkography. J Biomed Opt. 2013;18:020502. [3] Spinelli AE, Schiariti MP, Grana CM, Ferrari M, Cremonesi M, Boschi F. Cerenkov and radioluminescence imaging of brain tumor specimens during neurosurgery.J Biomed Opt. 2016 1;21(5):50502. [4] Glaser AK, Davis SC, McClatchy DM, Zhang R, Pogue B.W. Gladstone, D.J. Projection imaging of photon beams by the Cerenkov effect. Med Phys. 2013;40:012101. [5] Glaser AK, Davis SC, Voigt WH, Zhan R, Pogue BW, Gladstone DJ Projection imaging of photon beams using Čerenkov-excited fluorescence. Phys Med Biol. 2013;58:601–619. [6] Roussakis Y, Zhang R, Heyes G, Webster G, Mason S, Green S, Pogue B, Dehghani H. Real-time Cherenkov emission portal imaging during CyberKnife® radiotherapy. Phys Med Biol. 2015 Nov 21;60(22):N419- 25. [7] Jarvis LA, Zhan R, Gladstone DJ, Jiang S, Hitchcock W, Friedman O.D. et al . Cherenkov video imaging allows for the first visualization of radiation therapy in real time. Int J Radiat Oncol Biol Phys. 2014;89:615–622.

Symposium: Adaptive radiotherapy (both anatomical and ‘functional’ changes)

SP-0404 Development and Clinical Implementation of Image Registration and Dose Accumulation