ESTRO 36 Abstract Book

S86 ESTRO 36 2017 _______________________________________________________________________________________________

S. Ken 1 , F. Arnaud 1 , R. Aziza 2 , D. Portalez 2 , B. Malavaud 3 , J. Bachaud 4 , P. Graff-Cailleaud 4 , S. Arnault 5 , A. Lusque 5 , T. Brun 1 1 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Medical Physics and Engineering, Toulouse, France 2 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Radiology, Toulouse, France 3 Institut Universitaire du Cancer - Oncopole - CHU de Toulouse, Urology, Toulouse, France 4 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Radiotherapy, Toulouse, France 5 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Bureau des Essais Cliniques, Toulouse, France Purpose or Objective Focal brachytherapy is proposed in our institute as an alternative treatment to active surveillance for low-grade prostate cancer (PCa). This study aims at characterizing the tumor focus and its margin with multiparametric Magnetic Resonance Imaging (mpMRI) in order to prepare the clinical protocol of focal brachytherapy. Material and Methods Patients pre-qualified for this study were positive for PCa (Gleason 3+3) on a previous standard biopsy series. New series of mp-MRI-guided and ultrasound-targeted biopsies were performed and in total, 17 patients with confirmed tumor and diameter<20mm were included in this phase II clinical trial (NCT01902680). mpMRI were acquired on a 1.5T Magnetom Aera Siemens scanner with 18-channel surface body coil. Anatomic imaging consists in Fast Spin Echo T2-weighted MRI (T2-MRI). In addition, same in- plane acquisition of functional Diffusion Weighted MRI (DWI-MRI) and Dynamic Contrast Enhanced MRI (DCE-MRI) were performed. After mpMRI registration, tumor volumes of interest (VOI) were drawn on anatomic T2-MRI. VOI and VOI+2mm were reported on functional DWI-MRI and DCE-MRI (Figure 1). Extracted parameters were Apparent Diffusion Coefficient (ADC) and KTrans. All parameters distributions were analyzed with Olea Sphere v3.0 and compared to contralateral normal appearing tissue. Focal brachytherapy was then delivered to all patients with linked 125 I seeds with a dose prescription of 152 Gy on the Planning Target Volume (PTV=VOI+2mm).

tumour model under realistic, i.e. harsh, conditions at experimental laser accelerators. Results: Both human tumour models showed a high take rate and continuous tumour growth after reaching a volume of ~5 – 10 cubic millimetres. Moreover, immunofluorescence analysis revealed that already the small tumours interact with the surrounding tissue and activate endothelial cells to form vessels. By analysing the dose dependent tumour growth curves after 200 kV X-ray treatment a realistic dose range, i.e. for inducing tumour growth delay but not tumour control, was defined for both tumour entities under investigation. Beside this basic characterization, the comparison of the influence of laser- driven and conventional (clinical Linac) electron beams on the growth of FaDu tumours reveal no significant difference in the radiation induced tumour growth delay. Conclusion: The mouse ear tumour model was successfully established and optimized providing stable tumour growth with high take rate for two tumour entities (HNSCC, glioblastoma) which are of interest for patient treatment with protons. Experiments comparing laser-driven and conventional proton beams in vivo as the next step towards clinical application of laser-driven particle acceleration are under way. Acknowledgement: The work was supported by the German Government, Federal Ministry of Education and Research, grant nos. 03ZIK445 and 03Z1N511. SP-0170 Novel models in particle biology research P. Van Luijk 1 1 van Luijk Peter, Department of Radiation Oncology, Groningen, The Netherlands The unique behaviour of particles that causes them to reach maximum dose deposition at the end of their track makes them useful for facilitating both treatment intensification and reduction of normal tissue damage. On a macroscopic scale particles facilitate reducing normal tissue dose and irradiated volume. Though it has been known for a long time that reducing the amount of irradiated normal tissue reduces toxicity, the increased precision of particles also makes sparing of substructures possible and offers more flexibility in choosing how to distribute inevitable excess dose over the normal tissues. However, it is also these unique properties that limit the information in available clinical data that can be used to guide optimal use of particles. Filling this gap is an important topic of particle radiobiology that has been approached with various in vivo models. On a microscopic scale particles deposit dose with a higher ionization density, especially near the end of the particle track, usually positioned in the target volume. Increased ionization density has been demonstrated to change response, both in terms of severity and potentially even in type. These effects have been studied mostly in 2D in vitro models. However, even though in 2D cell cultures differential effects between high- and low-LET radiation are observed, these models seem to be more radiosensitive than one would expect based on clinical data. Interestingly it has been observed that cells respond markedly different when irradiated in a more tissue- equivalent 3D culture system. Moreover, recent insights from stem cell biology indicate a potentially critical role of stem cells both in tumour and normal tissue response. Taken together, 3D culture systems based on tissue-specific stem cells may offer new opportunities to better understand the response of tumours and normal tissues to particle irradiation.

Results ADC parameters (mean, median, 25th and 75th percentiles) are found to be significantly lower in tumor volume (VOI) compared to contralateral normal tissue (p<0.012 for all ADC parameters), confirming diffusion tumor mass restriction. Different distributions of ADC and Ktrans were observed among patients (Figure 2). Majority (66.66%) of low ADC and abnormal Ktrans values were included in the VOI. Interestingly, the 2mm margin allows us to treat additional abnormal ADC and KTrans volumes on 1/3 of the patients.

Proffered Papers: Prostate 1

OC-0171 Multiparametric MRI margin characterization for focal brachytherapy in low-grade prostate cancer