ESTRO 38 Abstract book

S61 ESTRO 38

against standard of care (comparator: systemic treatment), address proper endpoints (cure, reduction of secondary metastases, prolongation of life, maintenance of quality of life?) and incorporate translational research. In order to be accepted by the community, these trials have to contain optimal imaging and treatment methods and include sufficiently large numbers of patients (multicentre efforts). During the presentation, I will highlight recent clinical studies in oligometastatic prostate cancer patients at different stages of disease and give a brief outlook on potential future studies the field of radiation oncology should embark on. 1 maria Sklodowska-Curie Memorial Cancer Center and Institute Of Oncology, Radiotherapy, Gliwice, Poland; 2 Maria Sklodowska-Curie Memorial Cancer Center And Institute Of Oncology, 3rd Radiotherapy Ward, Gliwice, Poland Abstract text The TNM staging system does not reflect the needs of radiation therapy in terms of prognosis in prostate cancer (PC) patients in terms of oligometastatic disease, both – in the case of lymph nodes as well as bone metastases. It describes only their presence and in the case of lymph nodes metastases – location (in or outside the pelvis). It is known that tumor control probability (TCP) depends on the number of clonogenic cells (which, probably indirectly, is reflected by tumor volume) and delivered dose. TCP could also be dependent on lesion location, which is connected with treatment precision and dose delivery possibility (surrounding critical structures). The last factor influencing TCP is the kind of metastases – lymph nodes vs bones. An additional point which should be considered is imaging – how to find them and which examination ought to be a standard. Because aforementioned issues, we have discussed the usefulness of PC oligometastases volumetric staging relying on our own material. This material comprised 165 PC oligametastases (94 in lymph nodes, 71 in bone - 118 patients) treated locally between 2011 and 2017 with SABR. Up to three metastases were accepted as oligometastatic disease. The total dose (TD) varied from 8 to 60 Gy and was delivered in fraction doses 6-15 Gy. Tumor volume varied from 0.1 to 68.2 ccm (mean 4.8, median 1.6). The median of tumor volume was 1.1 for lymph nodes and 4.0 for bone metastases). Lymph node metastases were mainly located in the pelvis (57). During FU (up to 74.6 months; median 15.7), the tumor volume, local control (LC), biochemical control (BC) and overall survival (OS) were evaluated. For statistical assessment the ROC and Youden index, logrank test and scatterplots were used. On the basis of ROC we specified 2 ccm as a threshold volume. There was a significant difference (p=0.03) in 50 months LC for these two groups (98% vs 75%). We did not find a statistically significant difference for the thresholds 3 and 4 ccm, but there was a clear separation of KM LC curves. We also found significant impact of tumor volume for BC among bone metastases (p=0.006). None of the other analyzed factors had an impact on BC. The obtained results suggest that features of oligometastases have not a significant impact on BC (probably it is linked more to systemic treatment), so when thinking about oligometastatic disease staging we should consider features of these lesions and local result. The basic examination to find such lesions should be probably PSMA PET, which is connected with the issue of volume evaluation (the SUV threshold). Finally, the PC oligometastases staging system ought to take into account the volume of metastases, their number and location (lymph nodes vs bones) when considering the anatomy SP-0119 What is the optimal staging for oligometastatic prostate cancer? L. Miszczyk 1 , A. Napieralska 1 , M. Miszczyk 2

SP-0116 Mechanisms of Radiotherapy Induced Inflammatory Signaling S. Harding 1 1 University Health Network, Princess Margaret Cancer Centre, Toronto, Canada Abstract text Radiotherapy directly leads to clonogenic cell death which is accompanied by inflammatory cytokine signalling. These cytokines have the potential to influence the immune system and may contribute to success of radiotherapy alone and in combination with immune checkpoint blockade. We have recently identified viral response proteins, the pattern recognition receptors (PRRs), as key drivers of this response. In this seminar we will discuss mechanisms by which radiotherapy induces PRRs, drives inflammatory signalling and contributes to the abscopal response in murine models of radiotherapy- immune checkpoint blockade treatment. The goal of these studies is to determine how inflammatory signalling is activated, whether it can be used as a biomarker of treatment response, and if it represents a novel means for improving cancer therapy. SP-0117 Neoantigens in cancers P.Kvistborg 1 1 The Netherlands Cancer Institute, Amsterdam, The Netherlands SP-0118 What are realistic clinical goals in radical radiotherapy for oligometastatic prostate cancer? T. Hölscher 1 1 Universitätsklinikum Carl Gustav Carus, Department Of Radiation Oncology / Oncoray, Dresden, Germany Abstract text Two decades ago, Hellmann and Weichselbaum postulated that for metastatic solid tumors a broad spectrum of transitional stages (spectrum hypothesis) exists, and that there may be an oligometastatic status potentially to be cured by ablative therapy. Next to the number of metastases (e.g. up to five?), the interval from treatment of the primary tumor and the pace of progression may define such an oligometatatic status. In prostate cancer (PCa), prostate specific antigen (PSA) is an established tumor marker that is well ahead of clinically significant disease, thus allowing for screening for oligometastatic disease at an early time point. Median time from PSA recurrence to symptomatic disease is 8 years after primary curative treatment, and 2,5 years in patients with castration resistant PCa without detectable clinical metastases, only. Beyond laboratory and pathology testing (Gleason score), modern anatomical and functional imaging (e.g. PSMA- PET-CT / -MR) has been shown to allow for an improved staging and thus a clinically sound patients selection. There may be different scenarios in prostate cancer, in which local ablative treatment of oligometastatic disease possibly plays a role: - Identification of metastatic disease in high risk primary PCa - Treatment failure after primary curative treatment in hormone-sensitive Pca - Definition of an oligoprogressive status in castration resistant Pca. Better clinical trials are urgently needed to establish the role of local ablative therapy in these cohorts of patients. These trials need to be competitive, i.e. randomized Abstract not received Symposium: Oligo-metastatic prostate cancer – shedding light in a quickly emerging field