[OA057] Comparative dose planning for Ru-106 brachytherapy and proton therapy for choroidal melanomas

Abstracts / Physica Medica 52 (2018) 1–98

high flux therapeutic beams. Two prototype devices for monitoring particle beams are under development, based on innovative silicon low-gain avalanche detectors optimized for time resolution (Ultra Fast Silicon Detectors – UFSDs). Preliminary results with proton beams are presented. Methods. UFSDs are low-gain avalanche detectors optimized for time resolution, where sensors as thin as 50 lm provide signals of  1 ns time duration with time resolutions of tenths of ps, and large enough signal-to-noise ratio to efficiently discriminate proton signal. One prototype device is being developed to directly count individual protons at high rates, while a second one is under investigation to measure the beam energy with time-of-flight techniques. This requires the design of custom UFSD sensors as well VLSI readout electronics. From simulations’ results and first beam tests with UFSD pads, strip detectors were produced, with two geometries (30 mm and 15 mm length) and different doping modalities to improve radiation hardness. In parallel, prototypes of a new readout chip have been submitted to the foundry. Results. Strips sensors were characterized in the laboratory through laser test and I(V) curve studies, and a test with a therapeutic proton beam, with energy ranging from 62 to 227 MeV, was done. Results were obtained via offline analysis of the collected waveforms for Boron and Gallium doped sensors. Time resolution of 35 ps, signal duration of ns, and good S/N separation were found. A gain degradation of 20% was founded in single pad sensors after 1012 protons/cm2 irradiation. Pile-up effects are under investigation. Conclusions. Based on the preliminary results, UFSDs are found to be a promising improvement of monitor chamber. The aim of this contribution is to review the advancement of the project and to report on the results of the test of UFSD strip sensors with a therapeutic proton beam. https://doi.org/10.1016/j.ejmp.2018.06.127

[OA056] Range uncertainty reduction in proton beam therapy via prompt gamma-ray detection Costanza Panaino a,*, Ranald Mackay b, Michael Merchant a, Stuart Green c, Ben Phoenix d, Tony Price d, Karen Kirkby a, Michael Taylor a a

University of Manchester, Institute of Cancer Sciences, Manchester, United Kingdom b The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom c University Hospitals Birmingham NHS Foundation Trust - Queen Elizabeth Hospital, Medical Physics Department, Birmingham, United Kingdom d University of Birmigham, School of Physics and Astronomy, Birmingham, United Kingdom ⇑ Corresponding author. Purpose. In proton therapy precise knowledge of the beam range is essential to guarantee the treatment’s efficacy and to avoid unnecessary toxicities. Over a fractionated course of treatment anatomical changes can severely impact the delivered dose distribution from that planned; evaluation of these changes on a fraction-by-fraction basis is essential. We report the first results of a new method to determine proton beam range in three dimensions, for pencilbeam scanning systems, with an uncertainty below 3 mm. Methods. The range is determined through the reconstruction of the origin of prompt gamma (PG) rays emitted from nuclear deexcitations following proton bombardment. PG emission is almost

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instantaneous and is characterised by a high-production rate. The prototype system is comprised of 16 symmetrically-spaced LaBr3 (Ce) detectors, in a spherical design. Initially the position reconstruction capability of the detector system was examined using Geant4 simulations. To determine the PG-rays emission positions in 3D, the information recorded by each detector is fed into a reconstruction algorithm, developed in the MATLAB environment. The development, testing and laboratory validation of the algorithm has been conducted using a sealed 60 Co source. Furthermore the algorithm has been employed to investigate, by means of Geant4 simulations, how the system performs with a proton pencil beam at different clinical energies. In the simulations a water phantom with 2-cm thick body materials slabs embedded inside has been modelled. Results. Preliminary simulation results show that for an ideal detector system the reconstruction algorithm is capable of determining the source position to within 1 mm in the 3D space. The algorithm is also able of discriminating between multiple sources with a relative separation of 0.15 mm. A good agreement has been observed between the dose and the prompt-gamma distribution from a proton pencil beam impinging the different phantoms at all the employed clinical energies. Conclusions. Proof-of-principle for the reconstruction algorithm with a sealed 60 Co source has been obtained. The response of the system with a clinical proton beam has been evaluated, by means on Monte Carlo simulations. The next stage is to test the system with a proton beam experimentally. https://doi.org/10.1016/j.ejmp.2018.06.128

[OA057] Comparative dose planning for Ru-106 brachytherapy and proton therapy for choroidal melanomas Charlotte Espensen a,*, Lotte Fog a, Juliette Thariat b, Joel Herault c, Marianne Aznar d, Celia Maschi e, Jean-Pierre Caujolle e, Jens Folke Kiilgaard f, Ane Appelt g a

Rigshospitalet, Department of Oncology, Section of Radiotherapy, Copenhagen, Denmark b Centre Francois Baclesse, University of Caen Normandy, Department of Radiation Oncology, Caen, France c Centre Antoine-Lacassagne, Department of Radiation Oncology, Nice, France d University of Oxford, United Kingdom e Centre Antoine-Lacassagne, Department of Ophthalmology, Nice, France f Rigshospitalet, Department of Ophthalmology, Copenhagen, Denmark g St James’s University Hospital, Institute of Cancer and Pathology, Leeds, United Kingdom ⇑ Corresponding author. Purpose. Eye-preservation using brachytherapy (BT) and proton therapy (PT) are commonly used as primary treatments for uveal melanomas (UM). Choice of modality generally depends on local availability rather than direct assessment of the two techniques. We conducted a comparative dose planning study, estimating biologically effective doses (BED) to the tumour, macula and optic nerve head (ONH). Methods. We retrospectively included 70 patients with primary UM: 35 treated with Ruthenium-106 (Ru-106) BT, and 35 who underwent PT. Only PT patients whose tumour was small enough to be treatable by BT were included. Prescriptions were 100 Gy (continuously delivered in a single session) for BT and 52 Gy (in 4 fractions) for PT to the entire tumour. Both planning techniques

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Abstracts / Physica Medica 52 (2018) 1–98

aimed to minimize doses to macula and ONH without compromising tumour coverage. Dual image-guided planning with 3D dose calculation was carried out for each patient. Dose volume histograms for tumour, macula, and ONH were extracted. BED was calculated using well-established models: Gagne et al. (Med Phys, 2012) for BT and Holloway and Dale (Br J Radiol, 2013) for PT, correcting for fractionation effects, overall treatment time and relative biological effectiveness. Wilcoxon signed-rank test was used to evaluate differences in BED. Results. Minimum tumour BEDs (BED99%) were larger for BT with median 159 Gy (interquartile range (IQR): 149–168) compared to 128 Gy (128–128) for PT. The median difference was 31 Gy (21– 41) with p<0.0001. Median macula BED50% was 72 Gy (22–587) for BT compared to 155 Gy (0–374) for PT. However, the median of the individual patient difference was 23 Gy (1–248, p = 0.0002), favoring PT. Median ONH BED50% was 46 Gy (15–291) for BT compared to 3 Gy (0–525) for PT but the difference was not statistically significant (p = 0.1). PT spared the macula for smaller tumours <2 mm from the macula, while the ONH received less dose with BT in juxtapapillary cases. Conclusions. Ru-106 brachytherapy delivered larger tumour doses, larger macula doses, and comparable optic nerve head doses compared to proton therapy. Large individual variations were seen, emphasizing the need for prospective comparative planning to guide the choice of treatment modality. https://doi.org/10.1016/j.ejmp.2018.06.129

[OA058] Inspire: Infrastructure in proton international research – A new horizon 2020 network Stine Korreman * Aarhus University, Department of Clinical Medicine, Aarhus N, Denmark Corresponding author.

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Objective. Proton beam therapy (PBT) is a radical new type of advanced radiotherapy, capable of delivering and conforming a targeted dose of radiation to the tumour while causing minimal damage to the surrounding healthy tissue. In the past 5 years there has been a huge investment in high energy PBT across Europe and eleven member states now either have PBT in operation or are developing this capability. In addition, the two largest manufactures of PBT equipment have based their manufacturing in Europe. This integrating activity INSPIRE, aims to link these clinical PBT centres in eleven different countries together with two associated centres in USA. It also brings in two of the worlds largest manufacturers of PBT equipment and an SME. The trans-national access in INSPIRE will provide European researchers with access to ‘‘state of the art” research capabilities employing proton beams at clinical energies. INSPIRE represents an integrating activity across Europe in a multi-disciplinary field that is growing exponentially. Through its Networking, Transnational Access and Joint Research Activities, INSPIRE seeks to provide the ‘‘state of the art” capabilities that are needed to address the key challenges in this rapidly developing field. INSPIRE has at its heart the principles of responsible research and innovation and will communicate its research and give access to its databases and software through an Open Access Gateway. INSPIRE will contain a pipeline of innovation through its Innovation Gateway, to accelerate research for patient and commercial benefit. INSPIRE will provide its researchers with an unrivalled research and training and opportunities to ‘‘discipline hop” into the industrial, clinical or industrial environment. INSPIRE integrates activities across Europe in this rapidly growing area and offers European researchers unrivalled access to state of the art research

capabilities in an area where there has already been significant government investment. INSPIRE is coordinated by the University of Manchester, and has 16 participating partners from 12 countries in Europe. https://doi.org/10.1016/j.ejmp.2018.06.130

[I059] Working in radiotherapy from the perspective of a nuclear medicine physicist Ronald Boellaard * University Medical Center Groningen, Nuclear Medicine and Molecular Imaging, Groningen, Netherlands ⇑ Corresponding author. Accurate and reliable PET/CT imaging is mandatory when performing quantitative assessment of radiotracer (FDG) uptake. This becomes even more important when PET is used in a radiotherapy (RTR) setting, either for assessment of target lesions, tumour delineation or response prediction and assessment. Moreover, there are specific requirements with respect to the imaging procedure when FDG PET/CT is used in a radiotherapy setting, such as e.g. the needs for a flat table, immobilisation devices equal to those used at radiotherapy and use of lasers for patient positioning. A specific challenge when PET is used for radiotherapy purposes is the exchange of knowledge and methodology between the nuclear medicine (NM) and radiotherapy physics disciplines. Often NM physicists are not aware of the specific RT requirements and applications, while RT physicists are not aware of the specific requirements for performing reliable PET imaging. In this presentation, requirements for reliable quantitative FDG PET/CT imaging from the NM physics perspective will be addressed. Technical and imaging physics related factors that affect PET image quality will be discussed as well as the need for standardizing imaging procedures and performing dedicated quality control procedures to assure harmonized performance (between systems and longitudinally). Finally, the impact of new PET/CT technologies, such as use of resolution modelling during reconstruction and digital PET detectors, on image quality and quantification and their relevance for RT applications will be reviewed. https://doi.org/10.1016/j.ejmp.2018.06.131

[I060] Working in radiotherapy from the perspective of an MRI physicist Lars E. Olsson * Lund University, Medical Radiation Physics, Department of Translational Medicine, Malmö, Sweden ⇑ Corresponding author. There is a substantial increase of imaging in the recent development in radiotherapy. The on-going process of installing dedicated radiotherapy MR-scanners in the oncology/radiotherapy clinics is an obvious proof of this development. MRI is a much more complex modality and applications extend from diagnosis to specific imaging for target identification, treatment planning, treatment follow-up and adaptive regimes. An in-house MR-scanner also brings along many safety issues, both for personnel and patients. Altogether, there is an increasing need for MRI expertise in the radiotherapy department. The demand on reliability and quantification of the data is considerably larger in therapy than diagnostic MRI applications. That