ESTRO 2022 - Abstract Book

S102

Abstract book

ESTRO 2022

Conclusion Automated NTCP-TCP-based optimisation is feasible and consistently outperforms manually generated VMAT plans in terms of NTCP and QOL scores. The highest QOL score was obtained for plans optimized prioritising the toxicities with the highest relative impact on QOL.

OC-0126 Novel methodology for re-irradiation treatment plan optimisation

L. Murray 1 , C. Thompson 2 , C. Pagett 2 , J. Lilley 2 , B. Al-Qaiseh 2 , S. Svensson 3 , K. Eriksson 3 , M. Nix 2 , M. Aldred 2 , L. Aspin 2 , S. Gregory 2 , A. Appelt 4 1 Leeds Institute of Medical Research at St James’s and Department of Clinical Oncology, University of Leeds and Leeds Cancer Centre, Leeds, United Kingdom; 2 Department of Medical Physics, Leeds Cancer Centre, Leeds, United Kingdom; 3 Research Group, RaySearch Laboratories AB, Stockholm, Sweden; 4 Leeds Institute of Medical Research at St James’s and Department of Medical Physics, University of Leeds and Leeds Cancer Centre, Leeds, United Kingdom Purpose or Objective The STRIDeR ( S upport T ool for R e- I rradiation De cisions guided by R adiobiology) project aims to create a clinically viable re-irradiation (reRT) planning pathway within a commercial treatment planning system (TPS) that takes account of the full previous dose distribution, fraction-size-effects, tissue recovery and anatomical changes between two radiotherapy courses. Materials and Methods The STRIDeR pathway allows an original dose distribution to be used as background dose to guide optimisation of a reRT plan. Organ at risk (OAR) planning objectives in equivalent dose in 2Gy fractions (EQD2) can be applied cumulatively across both treatment courses, with optimisation of the reRT plan performed on a voxel-by-voxel level in EQD2; this is a unique feature within a commercial TPS. Normal tissue recovery can be incorporated and different a/b values applied per OAR. Different approaches to image registration can be employed to account for anatomical change. Validation of the EQD2 optimisation process was performed and data from 21 patients who received 5-fraction pelvic Stereotactic Ablative Radiotherapy (SABR) reRT were used to evaluate the pathway. A selective approach for dose mapping was used: 1) the original planning CT was registered to the reRT planning CT with deformable image registration (DIR), and the original dose mapped to the reRT planning CT based on the deformation vector field; 2) for each OAR where the DIR was considered reliable, the original dose was used as background dose for reRT optimisation and cumulative planning objectives in EQD2 applied across both dose distributions (Fig 1); 3) for any OAR where the DIR was considered unreliable, the previous maximum dose to that OAR within 2cm of the reRT Planning Target Volume (PTV) was used to calculate the ‘dose remaining’ for reRT and then determine an appropriate planning objective, applied to the reRT dose distribution only. The PTV coverage was optimised in physical dose (applied to reRT dose distribution).

STRIDeR plans were compared to those produced using a standard manual method based on the same registration strategy.