Abstract Book

S191

ESTRO 37

SP-0374 Protons for oligometastases? M. Hoyer 1 , J.B. Petersen 2 1 Hoyer Morten, Danish Center for Particle Therapy, Risskov, Denmark 2 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus N, Denmark Abstract text Photon based stereotactic radiotherapy is the accepted standard radiation modality in therapy of metastases in the brain (SRT) or body (SBRT) and it is widely used for treatment of patients with one or few metastases. In most cases, the metastases are small and not located in close proximity to critical organs at risk. SRT and SBRT can therefore be employed with high doses and a low risk of complication. Protons have superior physical properties with distinct range and dose deposit in the normal tissue and they are often quoted to be more precise than photons. Pencil beam scanned protons may allow very conformal dose distribution. There are, however, certain limitations related to the physics and hardware that make protons less favorable in treatment of metastases. With the present technology, the lateral penumbra of scanned protons is less sharp than for IMRT, especially in treatment of smaller targets. On the other hand, the low dose volume and thereby the integral dose is always reduced with protons. Treatment of small targets with PBS is vulnerable and less robust to anatomical changes from day to day and during treatment and uncertainties in stopping power estimation. For SBRT of small lung and liver metastases, respiration related motion of ribs may degrade the planned proton dose distribution. The more resource- demanding proton SRT/SBRT is only preferred over conventional SRT/SBRT when it is related to a reduced risk of morbidity. In principle, scanned protons my be preferred for treatment of large metastases embedded in organs with large volume effects (parallel organized) that is sensitive to the integral or median dose whereas small metastases in close relationship to organs with low volume effects (serial organized) benefit from the less costly IMRT. This presentation will focus on the potential possibilities, the present knowledge and on the limitations in terms of physics and hardware for proton therapy of metastases and it will discuss how improvement of the technology with i.e. reduced spot size and collimated scanned beam may increase the usefulness of protons in treatment of metastases. SP-0375 Surveillance or metastasis-directed Therapy for OligoMetastatic Prostate cancer recurrence P. Ost 1 , D. Reynders 2 , K. Decaestecker 3 , V. Fonteyne 1 , N. Lumen 3 , A. De Bruycker 1 , B. Lambert 4 , L. Delrue 5 , R. Bultijnck 1 , E. Goetghebeur 2 , K. De Man 6 , G. De Meerleer 7 1 Ghent University Hospital, Radiation oncology, Gent, Belgium 2 Ghent University, Applied Mathematics- Computer Science and Statistics, Ghent, Belgium 3 Ghent University Hospital, Urology, Ghent, Belgium 4 Ghent University, Radiology and Nuclear Medicine, Ghent, Belgium 5 Ghent University Hospital, Radiology, Gent, Belgium 6 Ghent University Hospital, Nuclear Medicine, Ghent, Belgium 7 Ghent University, Radiation oncology, Gent, Belgium Purpose or Objective Retrospective studies suggest that metastasis-directed therapy (MDT) for oligorecurrent prostate cancer (PCa) improves progression-free survival. We aimed to assess the benefit of MDT in a randomized phase II trial. Material and Methods In this multicentre, randomised, phase II study, asymptomatic PCa patients were eligible in case of a biochemical recurrence following primary PCa treatment

Symposium: Oligometastatic disease

SP-0372 Oligometastases and Oligoprogression: Evidence for local treatment in metastatic disease N. Andratschke 1 1 University Hospital Zürich, Department of Radiation Oncology, Zurich, Switzerland Abstract text Although Hellman and Weichselbaum coined the concept of oligo-metastases as a distinct state with its own biology in 1995, it only recently started to be more thoroughly investigated in the context of stereotactic body radiation therapy (SBRT). Nevertheless, up until now, there is no unequivocal clinical proof that oligo-metastatic patients really do benefit from local interventions such as surgery, interventional radiology or radiotherapy (SBRT) with regards to overall survival. A possible hint for a benefit could be derived from surgical series of lung and liver metastases indicating worse overall survival after microscopic incomplete resection compared to complete resection, indicating the need for local control of the respective metastases. Besides, no clear definition of oligo-metastases exists. Currently, a maximum number of lesions and/ or organs involved are proclaimed to define this state, although no standardized agreement exists. In addition, a distinction between synchronous and metachronous oligo-metastatic situation as well as oligo-progression has to be made to fully cover a wide spectrum of biological behaviours. Due to technological innovations and based on positive experiences with treating primary non-small cell lung cancer patients, SBRT is increasingly adopted in the oligo-metastatic situation. Retrospective series, especially including pulmonary and hepatic metastases, report favorable outcome and reasonable toxicity profile. Recently, two prospective studies in oligo-metastatic lung cancer have shown superior progression-free survival with a strategy including vigorous treatment of all metastatic sites with radiotherapy. The current presentation will focus on a) the biology and definition of oligo-metastases and its different presentations, b) the rational of intensified local treatment, c) the role of SBRT and ideas to include knowledge of dose-response analyses in the decision- making process and d) current and future study activities that may answer some of the raised questions in the near future and finally, e) the possible expansion of SBRT in non-oligometastatic stage IV disease in the light of immunotherapy. SP-0373 Planning and delivery strategies for oligometastatic disease P. Kroon 1 1 UMC Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands Abstract text Treatments of oligometastases with stereotactic radiotherapy are becoming a common approach. The published studies show promising results with high rates of local control and a potential postponement of systemic therapy. Early results indicate that treatment related morbidity is limited. A striking aspect is that different centers report use of a variety of treatment planning and delivery strategies. The content of this lecture will be based mainly on peer reviewed papers supported with data from our institution. The topics will cover aspects of treatment planning and image guided treatment. Special focus will be on treatment of lymph node oligometastases.