ESTRO 38 Abstract book

S233 ESTRO 38

changes of the individual’s anatomy. The lecture will review options for IVD based on 2D detectors either place at the head of the linac for forward projected 3D IVD, or EPID detectors for back-projected 2D or 3D IVD. Clinical examples and challenges of IVD will be discussed.

Teaching Lecture: Importance of volumetric staging and biological dose inhomogeneity in IMRT

SP-0443 Importance of volumetric staging and biological dose inhomogeneity in IMRT \r B. Maciejewski 1 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Dept. Radiotherapy, Gliwice, Poland Abstract text Basic biological aim of radiotherapy is to kill tumour cells (stem and clonogenic cells) and kill them all to achieve the highest TCP. Therefore, dose fractionation should be tailored to the initial number of tumour cells, which strictly corresponds with tumour volume. However, fractionation schedule is still individually designed based on quasi-quantitative rank – TNM system, which radiobiologically sounds illogical. Within a given T stage, i.e. T 2 N 0 M 0 , there is at least one decade difference in tumour cell number between the smallest and the largest tumours within this T category but practically, prescribed total dose is usually the same. This problem is discussed in details and illustrated with own data and the published results. Simple methods, how to convert tumour volume into the number of tumour cells and to tailor dose- fractionation for the highest TCP as possible, using single parameter D 10 is presented. The use of Volumetric Staging instead of the TNM to plan optimal radiotherapy is documented by practical examples. In the era of the 3D, 4D-IMRT, IGRT, SHRS, Fowler strongly recommended to plan D 100 instead of D 95 for the GTV. Results of the own pilot study clearly show, that even small “cold spots” within GTV subvolume can ruin the TCP initially predicted. The study shows how important is to convert physical DVHs into Biologically Normalized Histograms (BNDVHs) and the way how to replan dose distribution within GTV to eliminate biological “cold spots” in order to estimate real TCP to be close or even equal to that initially prescribed. Main goal of the lecture is to convince the audience that clinical radiobiologic principles are undoubtedly a basic requirement of all 3D conformal radiotherapy strategies. Key words: 3D-IMRT, Volumetric Staging, biological dose fractionation planning, D 100 instead of D 95 , BNDVHs SP-0444 In-vivo dosimetry: Possibilities and Pitfalls V.N. Hansen 1 1 Odense University Hospital, Laboratory of Radiation Physics, Odense C, Denmark Abstract text In-vivo dosimetry (IVD) is the final verification of correct radiotherapy delivery. IVD is verifying that the radiotherapy plan, as designed within the treatment planning system (TPS), is delivered correctly to the individual patient, at the time of treatment. Historically IVD has focused on correct output of the linear accelerator and the focus has been point dose measurements. This is often measured as entrance dose verification, which does give assurance that at the specific point the output of the linac is correctly calibrated. This worked well in an era of simple open beams. However, the focus has changed from the “simple” output of the linac due to the fact that most TPS plans are IMRT or VMAT. Hence a point dose is no longer representative of the treatment. In addition the focus is not only on the capability of the linac delivery, but it is increasingly the patient anatomy and the possible Teaching Lecture: In-vivo dosimetry : Possibilities and Pitfalls

Teaching Lecture: The vital role of physicists in clinical trials: from design to data analysis

SP-0445 The vital role of physicists in clinical trials: from design to data analysis A.L. Appelt 1 1 University of Leeds & St James’s University Hospital, Leeds Institute of Medical Research and Leeds Cancer Centre, Leeds, United Kingdom Abstract text Medical physicists are vital players in the conducting of radiotherapy trials. Evidence clearly points to the importance of treatment quality assurance in clinical trials [1,2], where protocol violations and sub-optimal radiotherapy results in worse patient outcomes [3]. Consequently, the need for medical physics expertise for trial QA is well-recognised, and major organisations directly employ physicists to conduct multi-centre QA, e.g. in EORTC, IAEA, RTOG, TROG, and the UK RTTQA [4]. This lecture will argue, however, that the role to be played by physicists is considerably more extensive and more impactful than “just” thorough trial QA. Through specific trial examples, the impact of physicists on hypothesis generation, trial design, protocol development, and imaging / treatment delivery sub- studies will be demonstrated - and a case will be made for physics leadership on trials. Trials discussed will include an early phase dose finding trial [5] in head & neck cancer and a large multi-centre phase III trial in NSCLC [6]. Furthermore, the added scientific depth offered by radiotherapy physicists from exploratory secondary analysis of trial data will be touched upon (see e.g. [7]). Finally, we will go through some practical tips and tricks on how to get involved in clinical trials work - all directly sourced from physicists actively working on clinical trials. 1. Ohri N, Shen X, Dicker AP, et al. Radiotherapy protocol deviations and clinical outcomes: A meta-analysis of cooperative group clinical trials. J Natl Cancer Inst 2013;105:387-393. 2. Weber DC, Tomsej M, Melidis C, Hurkmans CW. QA makes a clinical trial stronger: evidence-based medicine in radiation therapy. Radiother Oncol. 2012;105:4-8. 3. Peters LJ, O’Sullivan B, Giralt J, et al. Critical impact of radiotherapy protocol compliance and quality in the treatment of advanced head and neck cancer: results from TROG 02.02. J Clin Oncol. 2010;28:2996–3001. 4. Melidis C, Bosch WR, Izewska J, et al. Radiation therapy quality assurance in clinical trials - Global Harmonisation Group. Radiother Oncol. 2014;111:327-9. 5. Rasmussen JH, Håkansson K, Vogelius IR, et al. Phase I trial of 18F-Fludeoxyglucose based radiation dose painting with concomitant cisplatin in head and neck cancer. Radiother Oncol. 2016;120:76-80. 6. Møller DS, Nielsen TB, Brink C, et al. Heterogeneous FDG-guided dose-escalation for locally advanced NSCLC (the NARLAL2 trial): Design and early dosimetric results of a randomized, multi-centre phase-III study. Radiother Oncol. 2017;124:311-317. 7. Yahya N, Ebert MA, House MJ, et al. Modeling Urinary Dysfunction After External Beam Radiation Therapy of the Prostate Using Bladder Dose-Surface Maps: Evidence of Spatially Variable Response of the Bladder Surface. Int J Radiat Oncol Biol Phys. 2017;97:420-426.