ESTRO 2020 Abstract book

S469 ESTRO 2020

In January 2019 the Danish Center for Particle Therapy (DCPT) treated the first patient. Beforehand, a team of specialists with interdisciplinary qualifications was put together to evaluate different fixation equipment and methods specific to proton therapy. In this presentation, we will share our experiences with equipment selection and the challenges that we have met in the implementation process. Furthermore, we will show some of the tools we use to help pediatric patients cope with positioning and immobilization. SP-0779 Treatment planning considerations in particle therapy I. Kristensen 1 1 Skåne University Hospital, Dept of Hemathology- Oncology and Radiation Physics, Lund, Sweden Abstract text The main advantage of proton beam therapy is the finite range and sharp distal dose fall off in depth. However, compared to photons, protons have additional sources of uncertainties that should be analysed and understood. Range uncertainties in proton therapy can be substantial, i.e. several mm. Therefore, range uncertainties play a critical role in proton planning and has an impact on the entire planning process that differs from photons. The PTV margin recipes used in photon planning, are typically not sufficient in proton planning. In proton planning, two margins have to be considered, the lateral margin and the margin in depth i.e. range uncertainty. In principle, these two margins are of different nature. According to ICRU 78 [1] the PTVs are recommended to be used in proton planning for dose reporting purposes. Additional volumes with margins that is individually specified (field-specific) have to be used to account for uncertainties in range. Paganetti has suggested a margin recipes that is widely used in proton planning [2]. However, some treatment planning systems offers robust optimization with field-specific margins as suggested by the user [3]. Consequently, the range uncertainty in proton planning also has an influence on the number of beams as well as the selection gantry angles. Robust planning have had the potential of mitigate the impact of range uncertainties. In this phase of the treatment planning process, proton planning emphasise other considerations than the photon planning. Plan robustness should be considered during the optimization as well as during the treatment plan evaluation, as well as the comparison with a photon treatment plan to choose the “best” treatment plan. Thinking protons instead of photons can be a great challenge. How to achieve the best plan? This includes selecting robust beam angles and thinking about what the protons interact with on its way to the target volume. Discussions about target volumes are frequent, as the use of them. Delineation is a major issue, not only for CTV/PTV but for other structures the protons might interact with in its beam path, as well as optimisation structures to provide the best treatment plan. References 1. Prescribing, Recording, and Reporting Proton-Beam Therapy. J ICRU Report 782007;7:NP 2. Paganetti H. Range uncertainties in proton therapy and the role of Monte Carlo simulations. Phys Med Biol ; 2012; 57(11):R99-R117 3. Li Y, Niemela P, Li L, Jiang S, Li H, et al. Selective robust optimization: A new intensity-modulated proton therapy optimization strategy. Med. Phys 2015;42(8):4840-4847

SP-0776 Workflow aspects for markerless tumor tracking - from imaging to delivery A. Skrobala 1 1 Greater Poland Cancer Centre, Department of Medical Physics, Poznan, Poland Abstract text Radiotherapy workflows involve a lot of different professionals and different stages. Workflow can integrate daily imaging with the radiation therapy delivery process. This presentation will focus on workflow aspects for markerless tumor tracking. Characteristics and influence of tumor motion in different treatment sites (e. g. lung, prostate, and liver) should be considered at each radiotherapy stage starting from the initial planning CT scan and ending on image-guided radiotherapy. The most important element of appropriate realized markerless tumor tracking is identification of tumor position in real time, compensation of tumor motion, repositioning beam in real time and adaptive dosimetry, which verify PTV coverage and OARs sparing, using real time tumor tracking. The aims of this presentation will be (a) ways of prediction of tumor motion by different motion management system both during imaging and radiotherapy delivery, (b) presentation of existing technology (e. g. robotic system and integrated-MRI treatment) for markerless tumor tracking and their limitations, (c) description of practical obstacles in daily positioning of the markerless tumor motion during imaging. Finally, the aspects will be presented on how to improve the accuracy of markerless tumor tracking. SP-0777 Clinical experience with markerless tumor tracking C. Bert 1 1 University Clinic Erlangen, Radiation Oncology, Erlangen, Germany Abstract text Dynamic tumor tracking (DTT) is one key feature of the Vero linear accelerator (Brainlab, Germany) that was developed dedicated to SBRT treatment. DTT can either be based on implanted fiducial markers which are in our case applied for liver cancer patients. Alternatively, DTT is used marker-less based on the image data only. This ML- DTT approach is in our clinic applied in lung cancer patients in particular since the implantation of fiducials bears the risk of causing a pneumothorax. The talk will cover a workflow description incl. treatment planning (margins), some data on delivery time, required personal, number of correlation models required, and the necessary imaging dose. These numbers are put into perspective to other DTT modalities in particular using the Cyberknife.

Symposium: Particle Therapy - possibilities and limitations

SP-0778 Positioning and immobilisation- challenges in particle therapy from a clinical perspective P. Randers 1 , M. Fuglsang Jensen 1 , M. Giørtz 1 , A. Schouboe 1 , K. Seiersen 1 , A. Vestergaard 1 1 aarhus University Hospital, Danish Center For Particle Therapy, Aarhus N, Denmark

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