ESTRO 2022 - Abstract Book

S246

Abstract book

ESTRO 2022

Results Trade-off PTV E volumes ranged from 6% to 73% of the total PTV E volume (Fig.2, right). The trade-off possibilities thus varied between patients. Reductions in OAR mean dose, NTCP, and PTV E coverage are shown in Fig.2 and below (median[min;max]). Contralateral submandibular [Gy] Glottic larynx [Gy] Esophagus [Gy] PTV E V 47.5Gy [%] TP 45 1.5[0.1;6.1] 1.9[-0.9;7.0] 1.8[-0.1;12.7] 2.4[1.2;5.2] TP 42.5 2.6[0.1;7.6] 2.9[-0.8;14.4] 2.7[0.4;13.8] 7.9[2.5;18.3]

Ninety-five percent (95%) of trade-off PTV E voxels below 47.5/45Gy in TPs were located within 10/4mm of the volume’s outer edge.

Conclusion We have demonstrated the possibility for substantial patient-specific reduction in OAR doses and NTCP by limited and well- controlled coverage reduction in elective target sub-volumes with low risk of microscopic disease spread. This workflow was made feasible by using automated multi-criteria optimization. The proposed method may present a step towards novel planning strategies which systematically include spatial variation in sub-clinical disease spread.

OC-0286 From PTV-based planning to robust planning: external validation of a robustness evaluation approach

R. Kierkels 1 , A. Minken 1 , E.W. Korevaar 2

1 Radiotherapiegroep, Department of radiation oncology, Arnhem/Deventer, The Netherlands; 2 University of Groningen, University medical center Groningen, Department of radiation oncology, Groningen, The Netherlands Purpose or Objective The traditional planning target volume (PTV) accounts for systematic and random treatment (e.g. setup) uncertainties, but assumes a static dose cloud approximation, that does not hold in areas with high density variations in both photon and proton treatments. In contrast, robust planning algorithms mathematically account for errors during plan optimization, but