ESTRO 2020 Abstract book

S220 ESTRO 2020

PFS-rates were 67.3, 56.0 and 41.1% in the TBI+IFRT arm and 58.0, 45.9 and 32.7% in the IFRT only arm, respectively. (Hazard Ratio=0.90 (95% confidence interval:0.62-1.30); p=0.559, adjusted for stage and LDH). There were no significant differences in OS.

oligometastatic prostate cancer where metastases- directed SBRT was compared with surveillance; systemic therapy in the form of androgen deprivation was not a component of the initial treatment strategy but used only at disease progression. In prostate cancer, the randomized phase III STAMPEDE trial addressed the hypothesis that local treatment of the primary tumor alone, without metastases-directed therapy, influences outcome in metastatic disease. Local radiotherapy of the prostate was shown to improve OS in the situation of low metastatic burden but not in high metastatic burden, compared to androgen deprivation therapy only. This presentation will discuss the local treatment modality used in these prospective clinical trials, in prospective single-arm trials as well as retrospective studies in the literature. Indirect comparisons between surgery and radiotherapy need to be performed as no head-to-head comparison is available. Comparison will be performed with respect to local efficacy, toxicity profile and possibility for combined modality treatment with chemotherapy and modern systemic treatment options. SP-0376 OligoCare: a pragmatic Observational basket study P. Ost 1 1 University Hospital Ghent, Radiation Oncology, Gent, Belgium Abstract text Stereotactic body radiotherapy has been widely adopted for the treatment of oligometastatic cancer despite the lack of level 1 evidence. Several trials are running to address this issue, but they will never answer all questions or capture differences in approaches in specific patient groups or countries. OligoCare is a prospective registry with the main objective to capture the patterns of care of radical radiotherapy for oligometastatic disease and identify factors influencing care. In the current presentation, an update will be provided on the progress of OligoCare over the last year since the start of the project. SP-0377 Challenges in radiotherapy planning and treatment guidance T. Janssen 1 1 Netherlands Cancer Institute, Radiotherapy, Amsterdam, The Netherlands Abstract text Stereotactic irradiation of oligometastatic disease provides an aggressive local treatment, with good local control and acceptable toxicity. Typically an inhomogeneous target dose is combined with steep dose fall-off, in order to achieve organs-at-risk or PRV constraints. However, with the high fraction dose, risk of serious toxicity is not negligible. Meeting the OAR constraints might not always be feasible, leading to different planning strategies, with a different trade-off between local control and robustness of meeting the OAR constraints during treatment. Image guidance of oligometastatic disease comes with its own challenges, depending on the location of the target. Improved imaging using for example 4D CBCT or MR guidance might decrease margins and thus influence the planning strategy. Moreover with the advances of online replanning, OAR sparing and dose escalation might become feasible in more complex situations. Even in the presence of good image guidance and motion management however, uncertainties remain. Examples include: machine, registration and

Conclusion Based on this trial, it cannot be concluded that TBI+IFRT is superior to IFRT in terms of PFS in patients with early stage indolent NHL. Acute and late toxicity were limited after IFRT with/without low dose TBI. Second primary malignancy was the main cause of death in both treatment arms. Low dose TBI induced a CR(u) rate of 33.3%.

Joint Symposium: ESTRO-EORTC: Redefining oligometastatic disease: incorporating advanced imaging into clinical trials

SP-0375 The role of radiotherapy in current management of oligometastatic patients M. Guckenberger 1 1 University Hospital Zürich, Department of Radiation Oncology, Zurich, Switzerland Abstract text Hellman and Weichselbaum first proposed oligometastatic disease (OMD) as a distinct cancer state between locally confined and systemically metastasized disease in 1995. In such patients with limited metastatic disease, the value of integrating local metastases-directed therapy into the treatment paradigm has been investigated in five randomized phase II studies. Three of these have assessed whether the addition of metastases-directed local therapy to standard-of-care systemic therapy improves outcome in OMD, as compared to systemic treatment alone. All three studies reported improved progression-free survival (PFS) or overall survival (OS). Palma et al. described an OS benefit of metastases-directed stereotactic body radiotherapy (SBRT) in addition to standard-of-care for OMD patients with controlled primary malignancy in a tumor-agnostic trial of mostly breast, lung, colorectal and prostate cancer. Ost et al. used a study design in