ESTRO 2021 Abstract Book

S163

ESTRO 2021

undergo surgical resection of early stage lung cancer. During the last years, we have, e.g., obtained knowledge on the effect of increasing radiation dose and on the (changing) referral patterns of patients. Moreover, clinical studies have addressed the question of using SBRT in (ultra)central lung tumours, in small primary tumours in more advanced disease and of the added value of SBRT in oligometastatic (non-small cell) lung cancer patients. This presentation for radiation oncologists and radiologists will highlight the current status and challenges of using SBRT in lung cancer patients.

SP-0243 SBRT - A new frontier for primary kidney cancer S. Siva 1 1 Peter MacCallum Cancer Centre, Radiation Oncology, Melbourne, Australia

Abstract Text

Conventional radiotherapy previously had a limited role in the definitive treatment of renal cell carcinoma (RCC), owing to the disappointing outcomes of several trials and the perceived radioresistance of this type of cancer. In this context, radiotherapy has been relegated largely to the palliation of symptoms in patients with metastatic disease, with variable rates of response. Following the availability of newer technologies that enable safe delivery of high-dose radiotherapy, stereotactic ablative radiotherapy (SABR) has become increasingly used in patients with primary RCC. Preclinical evidence demonstrates that RCC cells are sensitive to ablative doses of radiotherapy (≥8–10 Gy). Trials in the setting of intracranial and extracranial oligometastases, as well as primary RCC, have demonstrated excellent tumour control using this approach. More recently, SABR has been applied to the new frontier of primary kidney cancer. Just as in the approach adopted through partial nephrectomy, understanding how to achieve the ‘trifecta’ of tumour control, low morbidity and nephron preservation is key. Here we explore the historical application of radiotherapy, the current biological understanding of the effects of radiation, and the clinical evidence supporting the use of ablative radiotherapy in primary RCC. An overview of the expected clinical outcomes, and special scenarios such as the solitary kidney is explored. The purpose of this lecture is to propose that the frontier of SABR for primary RCC may be soon ready to crossed into the mainstream.

SP-0244 SBRT for liver tumours M. Lee Australia

Abstract not available

Joint symposium: ESTRO-ESR: MRI-guided radiotherapy in gynaecological cancer treatment

SP-0245 Functional MRI for cervical cancer E. Sala 1 1 University of Cambridge, Oncological Imaging, Cambridge, United Kingdom

Abstract Text Advances in cross sectional imaging have led to an increasingly important role for radiology in the management of cervical cancer. MRI is the imaging modality of choice for evaluation of disease extent, treatment selection (surgery versus radiotherapy) radiotherapy planning, treatment follow-up and detection of tumour recurrence. Advantages of MRI include superb spatial and tissue contrast resolution, no use of ionizing radiation, multiplanar capability and fast techniques. However, optimization of MRI sequences and clinical protocols is crucial in order to ensure best results. Basic MRI protocol for cervical cancer imaging includes T1-weighted (T1W) images in the axial plane and T2- weighted (T2W) images in the sagittal and axial oblique planes. T1W axial images with a large field of view to evaluate the entire pelvis and upper abdomen for lymphadenopathy as well as bone marrow changes are essential in evaluation of the extent of disease. High-resolution axial oblique T2W fast spin-echo (FSE) images taken parallel to the short axis of the uterine cervix are crucial in assessing parametrial invasion in patients with cervical cancer. Diffusion weighted imaging (DWI) can provide valuable information for pre-operative staging in patient with cervical carcinoma. DWI can also help in evaluation of tumour response to radiotherapy in patients with cervical cancer, MRI is the best single imaging investigation and can accurately determine tumour location (exophytic or endocervical), tumour size, depth of stromal invasion and extension into the lower uterine segment. On T1W images, tumours are usually isointense with the normal cervix and may not be visible. On T2W images, cervical cancer appears as a mass of intermediate signal intensity and is easily distinguishable from low signal intensity cervical stroma. They show restricted diffusion on the DWI. MRI is recommended in evaluating cervical carcinoma patients with clinical stage IB disease or greater when the primary lesion is larger than 2 cm because of a relatively high likelihood of parametrial invasion and/or lymph node metastases. The staging accuracy of MRI ranges from 75%-96%. The reported sensitivity of MRI in the evaluation of parametrial invasion is 69%, and the specificity is 93%. The most important issue in the staging of cervical cancer is to distinguish early disease (stage IIA1 and below), treated with primary surgery from advanced disease that is treated with radiation alone or in combination with chemotherapy. When the tumour invades beyond the uterus with parametrial invasion, it is defined as stage IIB . Spiculated irregular tumor / parametrial interface, soft tissue extension into the parametria or encasement of the peri-uterine vessels are required to make a confident diagnosis of parametrial invasion. MRI has a specificity and negative predictive value (NPV) of 97% and 100 % respectively in evaluating parametrial invasion. An important pitfall is the overestimation of parametrial invasion on T2W