ESTRO 2023 - Abstract Book

S713

Monday 15 May 2023

ESTRO 2023

Techniques will be presented for local and locoregional breast for challenging anatomies. The treatment planning for photon plans is performed using Eclipse (ARIA, Varian Medical Systems, Inc) with 6 and / or 10 MV beams or using Ethos Treatment Management (Varian Medical Systems, Inc), calculated using the Acuros algorithm. The proton plan is performed using Raystation (Raysearch laboratories). Results In many institutions, standard treatment techniques are applied for the different treatment sites. In our institution the standard techniques are tangential IMRT fields for local treatment and hybrid with a combination of open fields/IMRT fields and VMAT for locoregional and SIB. However, for challenging sites you sometimes have to deviate from the standard techniques. In addition, in The Netherlands, depending on age and risk factors such as heart, lung and contralateral breast dose, and other factors such as smoking or not, patients might be referred to a proton facility. In this presentation, examples of the standard treatment technique as well as chosen solutions for special cases will be presented. SP-0855 When and how to use a nodal boost W. Woodward 1 1 The University of Texas MD Anderson Cancer Center, Department of Breast Radiation Oncology, Houston, USA Abstract Text Nodal boosts are typically used in breast radiotherapy to target involved regional nodal areas not removed at surgery, or at risk of harboring residual disease in spite of surgery. Unfortunately, there is a paucity of prospective data to guide this practice. In this session we will review existing retrospective data, rational approaches based on first principles, and potential risks. We will discuss a potential guideline for clinical practice.

Symposium: Biologically-guided radiotherapy - Where are we now more than 20 years since the introduction of biological target volumes?

SP-0856 Biologically-guided target definition L. Dubois

Abstract not available

SP-0857 Biologically-guided dose prescription I. Toma-Dasu 1 1 Stockholm University and Karolinska Institutet, Medical Radiation Physics , Stockholm, Sweden

Abstract Text The progress and technological development of functional and molecular techniques for imaging the tumours has offered the possibility of defining the target in radiation therapy and devising the treatment in an innovative manner. The concept of Biological Target Volume (BTV) encompassing the multi-dimensional physiological and functional information provided by the new imaging techniques has been proposed many years ago and since then it has been a continuous challenge for the clinical community to define and apply it. There are several questions that arise: what are the key tumour features that could be derived from functional and molecular imaging, how should they be used for defining the BTV, what dose should be prescribed to the BTV to account for these features and, finally, how to deliver this dose in a safe and robust manner. The ultimate challenge would therefore be to use molecular and biological information from advanced imaging modalities for the individualisation and the adaptation of the treatment according to the key features of the patient taking into account the response of both tumours and normal tissues. A simplified approach would be to determine the critical radiobiological parameters influencing the radiation sensitivity of individual tumours before treatment, such as tumour metabolism, hypoxia, proliferation and density of clonogenic cells, based on PET-CT imaging using suitable tracers (e.g., FDG, FMISO, and FLT) and to include this biological information into the treatment planning. This approach therefore includes the critical step of deciding what dose should be prescribed and subsequently delivered based on the acquired knowledge about the tumour features derived from imaging - in other words the biologically-guided dose prescription. This talk would therefore focus on the current approaches for prescribing the dose after the definition of the BTV, starting from the empirical dose escalations to developing quantitative methods for incorporating PET-CT information on tumour clonogenic cell density, hypoxia and proliferation into the treatment planning and optimisation. The controversial approach of dose re-distribution will also be discussed. Particular attention will be paid to presenting the potential implications of not taking into account the intrinsic dynamic character of the features defining the BTV on the dose escalation in the typical dose painting by numbers or contours approaches. The mathematical formalism and the computational approach will be presented in detail as well as the pipeline for the implementation into a treatment planning system. Clinical examples for dose prescription based on tumour hypoxia and clonogen density for H&N carcinoma patients will be included. SP-0858 Biologically-guided treatment - How to plan, deliver and adapt M. Lazzeroni 1 1 Stockholm University, Department of Physics, Medical Radiation Physics division, Stockholm, Sweden Abstract Text Current clinical practice in radiotherapy is predominantly based on the physical optimisation of the dose distribution according to the anatomical information of the tumour and normal tissues. This often results in treatment strategies where homogenous dose distributions are planned to be delivered to the targets of interest. In most cases, clinical practice does not account for the radiosensitivity of individual patients, nor does it for the spatial and temporal heterogeneities of the tumour radioresistance before or during treatment. However, it is well known that the biological heterogeneity of the tumour may occur at multiple levels - as inter- and intra- patient variations - and evidence is accumulating that this may