ESTRO 37 Abstract book

S349

ESTRO 37

Abstract text Mega-voltage external beam robotic planning and treatment delivery is currently only offered in the commercial setting by one manufacturer. We utilise the CyberKnife® system (Accuray Incorporated, Sunnyvale, California) at our hospital. It uses a non-isocentric and non-coplanar approach for the majority of its workload and has an optional 6 Degrees of Freedom (6DOF) RoboCouch®. In our centre CyberKnife® is dedicated to Stereotactic Ablative Body Radiotherapy (SABR) and Stereotactic Radio-Surgery (SRS) only, as part of a large 11 linac department on two sites. As such we operate a large SABR lung practice on the linacs and more recently started treating selected oligo-metastatic cases on gantry-based linacs too. At a weekly SABR/SRS Multi- disciplinary Team (MDT) meeting we select the correct platform for treatment, based on the clinical indication and the most appropriate tracking methodology. Due to the nature of high SABR/SRS doses per fraction and small collimator sizes to achieve sharp dose fall-off and tight margins, robotic delivery can have lengthy treatment delivery times in the order of 45 to 90 minutes. As a consequence our aim is to achieve the most comfortable patient position possible, to ensure they remain still throughout treatment, minimising intra- fraction movement. Although the design of the robot accommodates patient movement and organ motion using real-time kilo-voltage (kV) imaging, there is a limit to what can be achieved. Employing the most appropriate tracking methodology to match the site to be treated is the first step. All intra- cranial sites are tracked using the skull as a surrogate, and extra-cranial sites close to or in a vertebral body are tracked on a short section of the spine. As each pair of kV images taken on-set is analysed the resulting residual displacement is corrected for in 6DOF by the robot at the next node (point in space) and beam delivery. These orthogonal image pairs are at a fixed position in the treatment room at 45 0 to the patient. Image analysis is almost instantaneous, but as Cone-Beam Computed Tomography (CBCT) is not available yet in-room, there is no three dimensional (3D) volumetric information. For soft tissues sites, and bony sites distant from the spine, fiducial marker tracking is used. To achieve rotational corrections a minimum of 3 markers must be inserted fulfilling strict geometrical criteria. A sub-optimal marker insertion or migration following the insertion may by necessity lead to rotations being disabled, thus reducing the accuracy of treatment delivery and leading to some uncertainty in dosimetry. Planning Target Volumes (PTV) margins can be modified up-front with this information in mind. Poor positioning and/or reproducibility of the patient can also lead to difficulties tracking e.g. unable to hold their arms up, very lateralised target with beams entering from the contra-lateral side, patients with a large Body Mass Index (BMI), erratic respiration patterns, or excessive respiration motion causing extremes of rotation. This presentation will discuss the challenges mentioned and suggest strategies to achieve the most optimal dosimetry and the most optimal patient position.

resonance imaging for non-small-cell lung cancer. Int J Radiat Oncol Biol Phys 2007; 68: 273-281. SP-0666 Automated treatment planning - from theory to practice E. Venema 1 , C. Timmermans 2 , J. Penninkhof 2 , S. Petit 2 , B. Heijmen 2 1 Erasmus MC Rotterdam, Cancer Institute, Pijnacker, The Netherlands 2 Erasmus MC Rotterdam, Cancer Institute, Rotterdam, The Netherlands Abstract text Usually, treatment plans are generated by dosimetrists in a trial-and-error process. Plan quality may then be affected by the dosimetrist’s planning skills and experience, and by available planning time. Recently, several systems have been proposed for planning automation, including Erasmus-iCycle/Monaco, with Erasmus-iCycle our in-house developed system for fully automated multi-criterial plan generation [1-2], and Monaco, our clinical TPS (Elekta AB, Stockholm, Sweden). Erasmus-iCycle generates a Pareto-optimal plan with clinically favourable trade-offs between all treatment objectives, while Monaco is used to convert the Erasmus-iCycle plan into a clinically deliverable plan. The quality of Erasmus-iCycle/Monaco plans is equal, or superior to the quality of manually generated plans [3-6]. The system is now in routine use for VMAT plan generation for prostate cancer, head-and-neck cancer, cervical cancer (plan-of-the-day adaptive therapy), and advanced lung cancer. The system is clinically used since 2012. In this presentation aspects of practical implementation of automated planning will be discussed with an accent on challenges for converting scientific success into an application for routine practice. [1] Breedveld S, Storchi PR, Voet PW, Heijmen BJM. iCycle: Integrated, multicriterial beam angle, and profile optimization for generation of coplanar and noncoplanar IMRT plans. Med Phys. 2012; 39(2): 951-963. [2] Voet PW, Dirkx ML, Breedveld S, Fransen D, Levendag PC, Heijmen BJM. Toward Fully Automated Multicriterial Plan Generation: A Prospective Clinical Study. Int J Radiat Oncol Biol Phys. 2013; 85(3): 866-72. [3] Voet PW, Dirkx ML, Breedveld S, Al-Mamgani A, Incrocci L, Heijmen BJM Fully Automated Volumetric Modulated Arc Therapy Plan Generation for Prostate Cancer Patients. Int J Radiat Oncol Biol Phys. 2014; 88(5):1175-9 [4] Sharfo AW, Breedveld S, Voet PW, Heijkoop ST, Mens JM, Hoogeman MS, Heijmen BJ. Validation of Fully Automated VMAT Plan Generation for Library-Based Plan- of-the-Day Cervical Cancer Radiotherapy. PLoS One. 2016; 11(12): e0169202. [5] Della Gala G, Dirkx ML, Hoekstra N, Fransen D, Lanconelli N, van de Pol M, Heijmen BJM, Petit SF. Fully automated VMAT treatment planning for advanced-stage NSCLC patients. Strahlenther Onkol. 2017;193(5):402-409. [6] Buergy D, Sharfo AW, Heijmen BJ, Voet PW, Breedveld S, Wenz F, Lohr F, Stieler F. Fully automated treatment planning of spinal metastases - A comparison to manual planning of Volumetric Modulated Arc Therapy for conventionally fractionated irradiation. Radiat Oncol. 2017 12(1): 33. doi: 10.1186/s13014-017-0767-2. SP-0667 Robotic Planning: achieving dosimetric optimisation through optimal patient comfort and positioning. H. Taylor 1 , C. Meehan 2 , P. Sturt 2 , N. Fotiadis 3 1 Royal Marsden Hospital, Radiotherapy Dept, LONDON, United Kingdom 2 Royal Marsden Hospital, Physics Dept, London, United Kingdom 3 Royal Marsden Hospital, Radiology Dept, London, United Kingdom

Symposium: Implications of the ageing population for radiation oncology

SP-0668 Integrated care for older radiotherapy patients A. O'Donovan 1 1 Trinity Centre for Health Sciences St James Hospital, Discipline of Radiation Therapy, Dublin, Ireland