ESTRO 2025 - Abstract Book

S4337

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

The highest overall plan score was for 3 5,5 , achieving normalized and weighted scores of 82.45% (nominal) and 75.81% (simulated). The lowest score was observed in 5,7 , with 19.46% (nominal) and 32.32% (simulated), as detailed in Table(1).

Conclusion: STP demonstrates benefits in organ-at-risk sparing and dose distribution but requires slightly longer treatment time and complex positioning protocols. In contrast, RTP offers a consistent, adaptable treatment approach, though with increased computational requirements and comparatively lower plan performance.

Keywords: radiotherapy, prostate cancer, lymph node

1514

Proffered Paper Comparison of spinal cord contouring and dosimetry in standard versus online MR-linac adaptive workflows in spine stereotactic radiotherapy (SBRT) Simon Page 1 , Merina Ahmed 2 , Alex Dunlop 3 1 Clinical Oncology, University Hospitals Sussex, Brighton, United Kingdom. 2 Radiation Oncology, Royal Marsden Hospital, London, United Kingdom. 3 Physics, Royal Marsden Hospital, London, United Kingdom Purpose/Objective: Geometric uncertainties likely result in excess dose to the spinal cord (SC), or the planning risk volume (PRV) [1-3]. The true position of the spinal cord is subject to error. Radiotherapy planning scan fusion, delineation, online daily imaging registration and inter/intra-fraction motion during treatment contribute to this error. We utilised an online MR-linac (MRL) adaptive workflow to assess SC delineation, reduction in excess SC dose, and the benefits to target coverage in comparison to standard spine SBRT workflows. Material/Methods: Five patients underwent standard workflow radiotherapy planning CT and MRI imaging and fusion (CT/MR). Patients had two additional MRL imaging sessions to represent online daily imaging with each session acquiring two separate MRI image sequences (MRLT2 and MRL3Dvane). Five clinicians delineated SC contours using CT/MR image