ESTRO 2022 - Abstract Book

S476

Abstract book

ESTRO 2022

For the treatment planning (TP) part , CT scans with GTV, PTV and OAR delineated were distributed to six dose planners. Two rounds were conducted. TP1: Five cases. >95% of PTV should be covered by 95% of 56Gy. Dose to the GTV should be as high as possible. Constraints were set for all OAR and had higher priority than GTV dose and PTV coverage. Discussion at a consensus meeting. Maximum dose of 85Gy was set for the mean dose to the GTV. TP2: Dose plans for two new cases. Results The median H mean was ≤ 1mm. The median H max was significantly shorter (p<0.05) for D3 (13mm), than for both D1 (21mm) and D2 (19mm). OAR delineation variation between centres resulted in high variabilities in OAR dose for simulated plans. In six plans for each of D1-D3, the variability in lobar bronchus delineation led to potential overdosage (constraint: D0.03cc<45Gy), with max D0.03cc of 58Gy (D1), 50Gy (D2) and 50Gy (D3) (Fig 1). For the mediastinal tissue, the constraint (D0.03cc<45Gy) was violated for the majority of the delineations in all three rounds, with max D0.03cc of 84Gy (D1), 85Gy (D2) and 72Gy (D3). 10 (D1), 14 (D2) and 4 (D3) plans led to mediastinal tissue dose >70Gy (Fig 1). For the dose planning study, the range of the standard deviation for GTV mean dose was 12.8-18.5Gy in TP1 and 2.8-3.5Gy in TP2 (Fig2).