ESTRO 2025 - Abstract Book

S4311

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Table 3: New proposed margin PTV Name

Expansion from CTVp Lateral Inferior

Posterior

Anterior

Superior

PTVp_S_5500 PTVp_I_5500 PTVp_L_5500

0.8cm 0.8cm 0.8cm

0.5cm 0.5cm 0.8cm

0.5cm 1.0cm 1.2cm

0.5cm 1.5cm 2.0cm

0.5cm 1.5cm 2.5cm

Figure 1: Shows the plan selection logged against max lateral extension of bladder per fraction of treatment.

Conclusion: The results suggest that an increase in the lateral margin for the small plan could improve its utilisation. However, further data would need to be collected post-implementation to ensure the desired impact is achieved.

Keywords: Adaptive, Bladder, Margins

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Poster Discussion Simulation-free online adaptive radiotherapy for patients with metastatic spinal cord compression – a feasibility study Lisette J Sandt, Lina M Åström, Anna M Nielsen, Evangelos Giannoulis, Laura A Rechner, Jens Edmund, Gitte F Persson Department of Oncology, Copenhagen University Hospital – Herlev and Gentofte, Copenhagen, Denmark Purpose/Objective: Purpose/objective: Metastatic spinal cord compression (MSCC) affects one in five patients with advanced cancer and requires urgent treatment. Palliative radiotherapy aims to relieve pain and prevent the progression of neurological symptoms. Acquisition of the planning CT for treatment planning often involves lengthy stays and return visits, which can be exhausting for frail patients. A simulation-free approach, using the patient’s diagnostic CT for treatment planning, eliminates the need for a separate planning CT. Combined with cone-beam CT (CBCT)-guided online adaptive radiotherapy (oART), this allows real-time adjustment of the treatment plan by accounting for daily changes in position and anatomy. The study aimed to evaluate the feasibility and time consumption of different simulation-free oART workflows for patients with MSCC to identify the most suitable option for clinical implementation.