ESTRO 38 Abstract book

S356 ESTRO 38

available in support of SBRT in the metachronous oligometastatic state across many tumor types. In synchronous oligometastases, the findings from 3 small studies, including 2 randomized trials, suggested that adding local ablative therapy (including SBRT) in such patients could improve progression-free survivals (ranging from 9.7-11.9 months) versus only standard of care (range 3.5-3.9 months) [Gomez DR, Lancet Oncol 2016; Iyengar P, JAMA Oncol 2017; Petty WJ, IJROBP 2018]. An update from one such study suggested that the overall survival was also improved by the addition of local ablative therapy [Gomez DR, ASTRO 2018]. However, there is a clear need to perform adequately powered, prospective randomized clinical trials to address this issue, especially given recent improvements in systemic therapy of NSCLC patients without any driver mutation. Recently, a multi- disciplinary group recommended guidelines for conducting trials of synchronous oligometastases, whichcould serve to have ensure more uniform trial eligibility criteria [Dingemans A, WCLC 2018]. The key elements of this document were as follows: (i) The definition, based on a systematic review, is to have a maximum number of 5 metastases, and limited to 3 organs. (ii) Eligible patients should have disease where a radical treatment is technically feasible with acceptable toxicity, taking into account all sites, that may modify the course of disease leading to a long-term disease control. (iii) All disease sites must be technically and safely treatable aiming for long-term control. (iv) Mediastinal lymph node involvement must be considered as locoregional disease in this definition. Other issues relating to trial design, as well as technical challenges in SBRT delivery, will be addressed during the talk. SP-0679 Challenges in SBRT physics T. Kron 1 1 Peter MacCallum Cancer Center, Physical Sciences, Melbourne, Australia Abstract text Background: Stereotactic Body Radiation Therapy (SBRT) has become in very short time an accepted treatment approach within radiation oncology. SBRT utilizes many features of modern radiotherapy technology, such as image guidance, motion management and small often intensity modulated fields, to deliver high biologically effective doses of radiation in very few fractions. It is the purpose of this presentation to highlight technological challenges in this context. Argument From a physics perspective challenges in SBRT can broadly be divided into three groups related to: i) equipment and software, ii) patient selection and set-up, and iii) target definition and re-identification during image guidance. Commissioning of equipment, such as 4DCT and small field dosimetry, has traditionally the first hurdle for the implementation of SBRT. For most of these tasks there are now standard solutions, protocols and recommendations that provide guidance for this work. While there are always emerging issues such as the combination of contrast injection and motion management, technical progress with equipment and the emergence of audits specifically designed for SBRT delivery contribute to generally safe implementation pathways. Patient positioning and immobilization may be more challenging as each patient is different. Long treatment times and various motion management options add to the complexity. Reproducibility of set-up feeds directly into decisions as to what image guidance method is appropriate and how frequently it would need to be applied. A particular challenge is the fast and reliable interpretation of the acquired images, which in many institutions leads to the requirement of radiation oncologists being present during image guidance.

consider regarding the Integration with systemic therapy. When detected at diagnosis, we also have an evolving understanding on the management of the primary tumour. The technical issues of delivering ablative or potentially immuno-stimulatory radiotherapy to such lesions raise their own challenges. Here we will explore the biology, technology and ongoing clinical trial activity in the oligometastatic state of prostate cancer. SP-0678 SBRT for oligometastatic NSCLC S. Senan 1 1 VU University Medical Center, Radiation Oncology, Amsterdam, The Netherlands Abstract text The oligometastatic paradigm suggests that patients with a limited number of metastases should be amenable to a curative treatment approach. The existence of an oligometastatic disease state in NSCLC is gaining acceptance. In the eighth edition of the American Joint Committee on Cancer staging system for lung cancer, a single extrathoracic metastasis (M1b) is staged as a separate disease entity than are patients with more widespread metastases (M1c). New insights in tumour biology also support the concept of aggressive treatment for oligometastases in order to improve outcomes [Turajlic S, Science 2016]. Metastatic spread can take place through multiple routes and in different directions, with metastases continuing to evolve after they have disseminated from the primary tumour. Potentially, metastases can re-infiltrate the primary tumour or surgical bed, a process called self-seeding. In addition, cross-metastatic seeding can occur, resulting in complex subclonal mixtures in the metastases themselves. Metastases present at the time a primary tumour is diagnosed are termed synchronous, whereas lesions presenting later (generally >3 months) are referred to as metachronous metastases. In contrast to the considerable body of evidence in support of ablative stereotactic radiosurgery in patients with brain metastases, evidence in support for SBRT to oligometastases at any extracranial site was poor until recently. In metastatic NSCLC with so-called druggable mutations, the advent of effective systemic treatments has led to changes in ESMO and NCCN guidelines, both of which now recommend the ablative treatment of isolated lesions that grow after an initial response (oligorecurrence), or which fail to respond completely (oligopersistence). An individual patient data meta- analysis in 757 patients with 1-5 synchronous or metachronous metastases identified 3 prognostic risk groups by recursive partitioning analysis [Ashworth A, Clin Lung Cancer 2014]. A good prognostic group identified were patients presenting with metachronous metastases (5-year Overall Survival 48%), an intermediate risk group presenting with synchronous metastases and no nodal metastases (5-year Overall Survival 36%), and a poor prognostic group with synchronous metastases and regional nodal disease (5-year Overall Survival 14%). Direct evidence for SBRT in metachronous disease has come from the SABR-COMET trial, which randomly assigned 99 patients who had a controlled primary malignancy and 1-5 metastatic lesions to receive either palliative standard of care (SOC) treatments alone [control arm] or with SABR to all metastatic lesions [SABR arm] [Palma DA, ASTRO 2018]. Of these, 19 patients had a diagnosis of lung cancer. Median overall survivalwas 28 months in the control arm (95% CI 19-33 months) versus 41 months in the SABR arm (95% CI: 26 months to ‘not reached’; p=0.09). Median progression-free survivals were 6.0 months (95% CI: 3.4-7.1 months) versus 12 months, respectively (95% CI: 6.9-30 months; p=0.001). Although grade 3 and higher toxicities were commoner with SBRT, no decreases in quality of life were observed. These findings represent the strongest clinical evidence