ESTRO 2021 Abstract Book

S12

ESTRO 2021

Abstract Text In this presentation we will explore the current status of CT based biomarkers. We will discuss how to develop and validate CT based imaging biomarkers and how these can impact clinical practice. A review of CT based biomarkers will be presented with the exemplar biomarker for discussion being measurement of sarcopenia - muscle characteristics - on CT and its use as a quantitative measure of patient's frailty.

Symposium: RTT-led radiomics research

SP-0035 Personalised breast cancer treatment using radiomics W. Tran Canada

Abstract not available

SP-0036 MR radiomics in prostate cancer M. Leech 1 1 Applied Radiation Therapy Trinity College, Trinity St. James's Cancer Institute, Radiation Therapy, Dublin, Ireland Abstract Text This presentation will provide a summary of the current evidence to support the use of radiomics in the radiation therapy management of prostate cancer. The limitations of current prostate cancer risk stratification methods will be discussed and an outline how radiomics may be a useful tool to improve this process will be provided. The potential benefits and limitations of MR-based radiomics workflows in the radiation oncology context will be considered.

SP-0037 Head and neck radiomics in a toxicity prediction model A. Duffton United Kingdom

Abstract not available

Debate: Prostate cancer: Short treatments by SBRT or brachytherapy?

SP-0038 SBRT G. Marvaso 1 1 Istituto Europeo di Oncologia , Radiotherapy, Milano, Italy

Abstract Text Prostate cancer: Short treatments by SBRT or brachytherapy?

Radiotherapy (RT) is a well known, potentially curative treatment option for all risk scenario of localized prostate cancer (PCa). Since traditionally moderated hypofractionation requires an overall treatment time of approximately 6-8 weeks and brachytherapy (BT) is an invasive method with limited accessibility at many RT facilities, shorter and more convenient treatment schedules were advisable. A radiobiological rationale of the low α/β ratio in PCa and the technological advancement in treatment delivery have shown the effectiveness and the safety of Stereotactic Body RT (SBRT), both in terms of oncological outcomes and toxicity profile. SBRT is a highly conformal RT technique enabling to delivery ultrahypofractionation and also shortening the overall treatment time. Recent published randomized trials confirmed that SBRT is safe and, for patients with low- and intermediate-risk PCa patients , offers excellent tumor control with an acceptable toxicity compared to conventional RT. Based on these results, three extremely hypofractionated schedules (36.25 Gy at 7.25 Gy/fraction, 37 Gy at 7.4 Gy/fraction, and 40 Gy at 8.0 Gy/fraction) have been included in the last versions (2021) of the National Comprehensive Cancer Network (NCCN) guidelines as Level 2A treatment options for PCa patients staged from very low to favorable-unfavorable intermediate-risk and finally to high risk (HR) group. Actually the available studies show that SBRT can be safely administered with excellent outcome in patients with low- and intermediate-risk PCA while the role of in HR PCa patients remains uncertain, since only few patients were included in the conducted clinical trials. Theoretically dose escalation in hypofractionated schedules is expected to achieve better clinical outcome results for high risk PCa patients as recently reported in the HYPO-RT-PC phase III non-inferior trial, regarding both failure-free survival and longterm toxicity for a ultra-hypofractionated RT including also this setting of patients. Moreover dose escalation up to 50 Gy in 5 fractions to the whole prostate gland resulted into excellent oncological results in terms of biochemical control but be associated with more gastrointestinal (GI) and genitourinary (GU) toxicity. To overcome the risk of an higher toxicity and since it seems that the local recurrences occur usually in the intraprostatic dominant lesion (DIL) a strategy to escalate the dose without augmenting toxicity is escalating only the macroscopic tumour. Today, multiparametric magnetic resonance imaging (mpMRI) including T2-weighted (T2w) and diffusion- weighted (DWI) is most often used for DIL delineation and RT planning, in this way using hypofractionated whole gland SBRT in conjunction with focal tumour boosting, could enhance the tumor response without worsening toxicity.