ESTRO 2020 Abstract Book

S789 ESTRO 2020

planning comparison study of robustly planned PBS vs VMAT using cases and treatment planning parameters from the NeoSCOPE trial to establish any potential reductions in lung and heart dose that may reduce the incidence of post- operative pulmonary and cardiac toxicities. Material and Methods We created PBS and VMAT plans for four datasets from NeoSCOPE that had 4DCT-generated ITVs. PBS plans were robustly optimised on ITV (95% coverage) using 5mm setup uncertainty and 3.5% range uncertainty. Gantry angles of 135°, 180° and 225° were used. Second-to-worst ITV coverage were reported. VMAT was optimised to PTV (ITV+5mm margin) with all plans using one full 360° arc. Both plans were optimised using treatment parameters from the NeoSCOPE trial to a dose of 45Gy/25#. Additionally, we reported dose to V5 lung and V40 heart. Treatment planning and dose analysis were done on Pinnacle (Phillips, v14 (PBS) and v16 (VMAT)). Results

Table 1: Differences in mean dose, percentages for 30 Gy and 60 Gy volumes for rectal wall, anal wall and bladder and monitor units (MUs). Positive values indicate that these dose metric values were improved compared to the clinical plan. The average mean dose to the rectal wall was decreased with 0.9 Gy and for the anal wall increased with 0.6 Gy. The average V60 for the rectal wall was increased with 0.3% and the average V30 for the anal was increased with 0.7%. The other dose metrics were not significantly different. The MUs for the personalized plans are slightly higher and on average 729 MUs. A warm restart was ran to steer for an optimal PTV coverage and maximum dose. Dosimetry QA results were good. Conclusion Plan quality is in general the same when using automated personalized planning.The planning efficiency improved from 30 min to 10 min. It is feasible to implement this new treatment planning module in our clinic for prostate radiotherapy. PO-1471 Dosimetric comparison of neoadjuvant proton beam therapy vs VMAT in distal oesophageal cancer O. Nicholas 1 , A. Selby 2 , J. Lambert 3 , R. Hugtenburg 4 , S.H. Gwynne 5 1 Swansea University, Swansea University Medical School, Swansea, United Kingdom ; 2 Swansea Bay University Health Board, Department of Physics- South West Wales Cancer Centre, Swansea, United Kingdom ; 3 Rutherford Cancer Centres, Department of Physics, Newport, United Kingdom ; 4 Swansea University, Department of Medical Physics, Swansea, United Kingdom ; 5 Swansea Bay University Health Board, South West Wales Cancer Centre, Swansea, United Kingdom Purpose or Objective Despite established survival benefit, use of neoadjuvant chemoradiotherapy (NACRT) for oesophageal cancer remains low in the UK due in part to concerns of post- operative pulmonary and cardiac toxicities. Pencil beam scanning proton beam therapy (PBS) has the potential to reduce dose to lung and heart, therefore reduce these toxicities. NeoSCOPE is a UK phase II randomized control trial of two NACRT regimens in oesophageal cancer that undertook a rigorous RTTQA programme. We undertook a

Data Table: Results of dose comparison between PBS and VMAT