ESTRO 2022 - Abstract Book

S451

Abstract book

ESTRO 2022

Target volume coverage and organ-at-risk violation metrics for initial non-adaptive and adaptive plans were compared using non-parametric Dunn method with Bonferroni correction for multiple comparisons. Results N=15 patients (median age 58, range 39-76, 7/15 females (47%)) with oligometastatic lymph nodes (coeliac, pre-sacral, aortocaval, porta hepatis, mesenteric, common iliac and peri-pancreatic) were included ( Table 1 ). No CTCAE v4 G3 or higher toxicities were recorded on-treat or at two-week post treatment review. Median GTV and PTV volumes on reference plan were 13.51cc (IQR 5.73-61.44) and 50.45 (IQR 16.97-108.64) respectively. Median dose prescription was 40Gy (range 30-50Gy) in 3-5 fractions. All initial plans met hard OAR constraints. In total, 62 fractions were delivered, using daily adaptive plans with data available for 55 fractions. Target re-contouring resulted in median 0.24% (IQR -2.68 – 3.1%) volume change in GTV. There were no OAR violations on the base plans. On pre-adaptation plans, OAR violation occurred in 37/55 (67.27%) of fractions versus 5/55 on post-adaptation plans (9.09%; p<.0001**; Figure 1 ) Re-optimisation achieved a mean dose reduction to duodenum and stomach within 3cm of PTV of 27.46% (95%CI 33.34-21.57) and 28.03% (95%CI 36.24-19.82) in D(0.01cc) and D(0.5cc), respectively, whilst significantly improving PTV100, PTV95 and GTV100 coverage as well as GTVmean dose ( Table 1, Figure 1 ).

Conclusion Our data confirms findings from similar series 3 that SMART is well tolerated, safe and offers a favourable dosimetric profile and an improved therapeutic index in abdominal and pelvic sites

Proffered Papers: Highlights of Proffered Papers - Best Papers

OC-0503 Effect of dose and fractionation de-escalation in low-risk cervix cancer treated with EBRT and BT

M. Serban 1 , M. Gallois 2 , T. Urtubey 2 , R. Nout 3 , A. de Leeuw 4 , L. Fokdal 1 , M. Assenholt 1 , S. Spampinato 1 , K. Bruheim 5 , B. Segedin 6 , S. Chopra 7 , M. Schmid 8 , N. Nesvacil 8 , S. Ecker 8 , K. Kirchheiner 8 , R. Pötter 8 , H. Westerveld 9 , F. Huang 10 , L. Velema 11 , L.T. Tan 12 , M. Valgma 13 , H. Mathiesen 14 , J. Lindegaard 1 , I. Jürgenliemk-Schulz 4 , K. Tanderup 1 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 2 McGill University, Department of Physics, Montreal, Canada; 3 Erasmus University Medical Center, Department of Radiation Oncology, Rotterdam, The Netherlands; 4 University Medical Centre Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands; 5 The Norwegian