ESTRO 2020 Abstract book

S389 ESTRO 2020

which include the failed data point the covariance drops into the 0.1-0.3 range. Post motor replacement, the covariance of the failed leaves and other variables became similar to those around it.

Symposium: Challenging cancers

SP-0639 What is new in radiotherapy for soft tissue sarcoma? A.R. Lopes Simões 1 1 Royal Marsden Hospital- Institute Of Cancer Research, Rttqa Group, London, United Kingdom Abstract text Soft tissue sarcomas of the extremities (STSE) are rare cancers, accounting for 1% of all malignancies arising in adult, with 3,272 cases in the UK in 2010. The American cancer society estimates that 13,130 new soft tissue sarcomas will be diagnosed in 2020. Localized disease is potentially curable, with 5-year survival rates of 60% in high-grade disease. Radiotherapy (RT) is used in the management of STSE combined with surgery, either in the pre-operative, post-operative or definitive settings and for high grade STSE has been established as standard of care. Results of a randomised prospective study comparing surgery with adjuvant RT versus surgery alone showed that RT improved local regional control for high grade STSE. Since this study was published technology has evolved impacting RT techniques used for STSE treatments. Modern RT techniques will be discussed in this talk whilst also debating existing unmet needs in RT for STSE. O’Sullivan et al demonstrated local control rates and overall survival were equivalent with either pre-operative RT or post-operative RT. However, RT has been recommended for patients in the post-operative setting in response to concerns around increased incidence of wound complications in the pre-operative setting. Later on, long-term outcomes reported by Davis et al demonstrated that pre-operative RT would lead to the development of less normal tissue complications which translated into improved functional outcomes. This is due to pre-operative RT fields being smaller and radiation doses lower. Typically, pre-operative RT dose is 50 Gy in 25 fractions as opposed to post-operative 60 to 66 Gy in 30 to 33 fractions. Three-dimensional conformal RT (3DCRT) remains the standard of care for STSE. Studies have demonstrated that intensity modulated RT (IMRT) permits the same local tumour control and has the potential to reduce treatment- related morbidities. However, there has not been a phase III study directly comparing both approaches. IMRT (fixed field or rotational) produces more highly conformal plans compared to 3DCRT. This allows improved dose homogeneity across the target volume with, steep dose gradients at the edge of the PTV leading to reduced radiation dose to neighbouring normal tissue. Image- guided radiotherapy (IGRT) is essential in this scenario to ensure accurate target volume coverage in the IMRT era, particularly when considering the inherent challenges in treatment set-up and reproducibility for STSE and the potential changes in tumour volume during treatment. The role of radiotherapy in STSE continues to evolve, with a focus on areas including pre-operative or post-operative treatment selection, implementation of IMRT, dose modifications according to histological subtypes and adaptations during treatment. There is further scope for improvement especially with respect to the reduction of treatment-related side-effects, consideration of adaptive RT and the use of automated planning. This talk will present modern RT techniques whilst also debating existing unmet needs in RT for STSE and discuss how future RT and innovations could improve STSE

Conclusion MLC failures are often unexpected and act as a source of treatment disruption. Historical machine log data was analysed and cross-referenced against linac maintenance logs. The results of the analysis have shown that tracking MLC performance comparatively to other parameters could provide a way of predicting certain MLC failures ahead of time. Incorporating this knowledge into a proactive maintenance schedule could result in more efficient linac scheduling and less overall treatment disruption.